| Author | Message | ||
| Tim James (Tjames)
Registered Member Username: Tjames Post Number: 14 Registered: 8-2006 Posted From: 66.59.117.14 Rating: N/A |
Still trying to find someone who can give me some help wiring my SW4024 inverter. Specifically, I need to know how to acheive proper ground to neutral bonding. It's a single leg 120vac system with a generator. If someone has done this, could you please share a diagram and maybe even some part #'s for relays, etc. I posted a while back regarding this, and someone responded who had it figured out, but I wasn't able to get in contact with them via their e-mail...so, any help would be great! | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 65 Registered: 8-2006 Posted From: 207.231.81.154 Rating: N/A |
Still DON'T bond grounds to neutrals. Never ever! All it takes is a mis-wired park, or a broken neutral connection anywhere to energize the whole bus body if the neutral and ground are together! Technically, a reversed hot and neutral from the shore with a bonded ground should trip a circuit breaker, but we can't wire the bus wrong and take a much greater chance of trouble... In your distribution panel there must be two bus bars, one bonded to the case for all the grounds, the other insulated from the case for the neutrals. Inverter output goes into the panel. Shore hot goes to one normally closed terminal of a 30 AMP Double Pole, Double Throw relay, the shore neutral goes to the other. The generator hot and neutral go on the normally open terminals. Relay common terminals go to the inverter 120V input terminals. Buy the relay with a 120V coil, run a wire from the generator hot thru a 3-5Amp fuse to one coil terminal of the relay. Your generator stop button must be 2 pole, with one normally closed, the other normally open. The other coil terminal wires to the normally closed terminal of the button, the other button terminal to the neutral. This circuit gives the inverter shore power all the time, and transfers to the generator when it is running. The coil wire thru the stop button prevents compressor motors from trying to follow the generator when the stop button is pressed. HTH, George toddelec@psyber.com | ||
| Tom Caffrey (Pvcces)
Registered Member Username: Pvcces Post Number: 1039 Registered: 5-2001 Posted From: 65.74.69.234 Rating: N/A |
Tim, I believe that Gumpy Dog(Craig Shepard) and Sean Welsh have both made their diagrams available. If you do a search you should be able to find their work. Tom Caffrey PD4106-2576 Suncatcher Ketchikan, Alaska | ||
| Tim James (Tjames)
Registered Member Username: Tjames Post Number: 15 Registered: 8-2006 Posted From: 66.59.117.142 Rating: N/A |
George, Respectfully, that's not to code. Code says the ground and neutral must be bonded at the source of the power. So, for inverter power that means the bus panel. On generator, the panel bond must be lifted because of the bond in the generator. On shore power both of these must be lifted. I'm trying to figure out an automatic way to do this with relays. It gets a little tricky because the SW4024 only switches hot, not neutral. Therefore to lift the ground to neutral bond in the generator, you need to actually disconnect the neutral externally from the inverter. Tom, I've done all the searching I can, and can't find anything of that nature. If anyone has them, perhaps you could e-mail them to me. Many thanks. Tim | ||
| Duane Kaler (Duane)
Registered Member Username: Duane Post Number: 21 Registered: 5-2006 Posted From: 66.82.9.56 Rating: |
So let me understand this, you would put "code" above the safety of you and your loved ones? To hell with code, you never ever bond neutral to ground in a bus. Always safety first, Duane | ||
| Geoff (Geoff)
Registered Member Username: Geoff Post Number: 904 Registered: 12-2002 Posted From: 71.211.122.197 Rating: N/A |
I used a Grainger DPDT switch Part# 5X847 along with the dust cover #4A079 and a J-box. When using the inverter or generator (one wire 120v) the ground is bounded to the neutral at the generator, when the 50 amp shore power cord is plugged in, the ground switches to bound through the power cord to the outside source and cuts off the generator (even though I always shut the gen off first). I don't have a diagram of how I wired it (I figured it out by looking at the wires), and it has worked flawlessly for the past 5 years. BTW, I haven't run across it yet, but my understanding is that a GFI-protected 50 amp outlet will trip with this set-up so keep that in mind if you ever run across one. --Geoff '82 RTS AZ w/Trace SW2512MC | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 68 Registered: 8-2006 Posted From: 207.231.81.154 Rating: N/A |
Tim, Respectfully, I think your are trying to apply the NEC section for a main meter panel. Lets take this logic a step further. What would you do when the bus is connected to shore power? At the meter panel, the utility only provides hot & neutral, the neutral is connected to a ground rod at the meter. The bus panel then becomes a sub-panel by definition! I would like to ask you for a specific code section you are referring to. Then I would like to ask what will happen when you get a wiring error in a park, with the hot and neutral reversed, OR the neutral wire breaks anywhere between the sub-panel and the shore connection?(Like if one of your relays doesn't work?) If your neutral and ground are bonded together, THE ENTIRE METAL BUS IS ENERGIZED! You walk up to the door, and when you take hold, YOU complete the path to ground. If you're lucky and wearing shoes on dry ground, you'll only get a tingle. Slippers on damp ground is much more deadly. There was a post on this a couple of months ago, which drew at least 30 screaming replies like Duane's when someone wanted to connect grounds and neutrals, I will try and find it in the morning. I have held Calif. Contr's. Lic. #624299, Classes C10, which is general electrical, and C20, which is HVAC, for 16 years. I feel I am qualified to speak. I will be glad to discuss this further with you off board. My email is my last name, & the first four letters of electrical: toddelec@psyber.com | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 69 Registered: 8-2006 Posted From: 207.231.81.154 Rating: N/A |
Well, I couldn't stand it, went out to the truck and got out the Code Book. Section 551 applies to Recreational Vehicles and Parks. Section 551.54, on page 813 of the 2002 National Electric Code Handbook reads: "INSULATED NETRAL. The grounded circuit conductor (neutral) shall be insulated from the equipment grounding conductors and from equipment enclosures and other grounded parts. The grounded (neutral) circuit terminals in the distribution panelboard and in ranges, clothes dryers, counter mounted cooking units, and wall mounted ovens shall be insulated from the equipment enclosure. Bonding screws, straps, or buses in the distribution panelboard or in appliances shall be removed and discarded. Connection of electric ranges ...shall be made with four conductor cord and 3-pole 4-wire grounding type plug caps and receptacles." The whole reason for the second part of this section is so YOU DON'T GET AN INADVERTENT GROUND-NEUTRAL BOND IN AN APPLIANCE, and to keep us bus nuts alive! Next, a ground-neutral bond will trip the GFI in any size campground plug. | ||
| Tim James (Tjames)
Registered Member Username: Tjames Post Number: 16 Registered: 8-2006 Posted From: 66.59.117.173 Rating: N/A |
So what do you do about the fixed ground/neutral bond in the generator? | ||
| Duane Kaler (Duane)
Registered Member Username: Duane Post Number: 22 Registered: 5-2006 Posted From: 69.19.14.16 Rating: N/A |
That is a good question Tim. As I have not purchased my gen set yet, I am not familiar with the fixed ground to neutral bond. Is this common in all gen sets? If so there must be a SAFE way to deal with this. I am sure some one here will know. Good luck, Duane | ||
| Jack Conrad (Jackconrad)
Registered Member Username: Jackconrad Post Number: 525 Registered: 12-2000 Posted From: 76.3.170.93 Rating: N/A |
If your trasnsfer switch switches the neutral as well as the hot(s), which it should, you are disconnecting the generator neutral ground bond from the rest of the wiring circuits except when the generator is energized. Jack | ||
| Tim James (Tjames)
Registered Member Username: Tjames Post Number: 17 Registered: 8-2006 Posted From: 66.59.116.75 Rating: N/A |
The SW4024 ONLY switches the hot. | ||
| Chris Peters (Chris_85_rts)
Registered Member Username: Chris_85_rts Post Number: 2 Registered: 11-2006 Posted From: 66.194.150.45 Rating: N/A |
Basically I think everyone is fundamentally correct, it just needs to be explained more clearly. I think what is being discussed here is three independent "sources" of power, 1) Shore Power, 2) Generator Power, and 3) Inverter Power. These are independent "sources" because at any one time, you should be only having one of these provide power. How you achieve that is fundamental to the discussion. The reason I put sources in quotes is because you want the neutral/ground bond to be at the source of the power no matter which source you are currently running from, and NO neutral/ground bond from the other two sources. For example, if you are running on shore power, the shore panel provides the neutral/ground bond, and the genset and inverter neutral/ground bonds MUST be broken. In my case, I don't use a transfer switch, I remove my 4 prong 50A plug from the genset socket and plug into the shore power socket. This ensures I break the internal genset neutral/ground bond in favor of the shore power bond. If you have an automatic or manual transfer switch, you must have three relays (contactors) or switches to isolate the two hots and the neutral. The neutral must be switched just like the hots are switched. Of course that is the easy case. In the inverter case it is more difficult, since it is wired essentially in series with the genset and shore power, and can suppliment the shore power when needed. And now we are back the orignal question which was how to deal with the internal neutral/ground bond in the SW4024. A quick Yahoo search on "SW4024 Wiring Neutral" found this site with a very detailed description of how one person solved this problem. http://www.ourodyssey.us/bus-e-ac.html And another discussion on this site: http://www.busnut.com/bbs/messages/233/5651.html?1078870189 And yet another: http://www.gumpydog.com/bus/MC9_WIP/Electrical/Wiring/House_Wiring/AC_Electrical_Panel/ac_ electrical_panel.htm | ||
| Tim James (Tjames)
Registered Member Username: Tjames Post Number: 18 Registered: 8-2006 Posted From: 66.59.117.50 Rating: N/A |
OK. This is the string of posts that got this whole thing started... http://www.busnut.com/bbs/messages/233/5651.html?1078870189 Who's right??? I'm not an electrician, and there seems to be some disagreement among those of you who are. Some say don't bond at all, others say it's essential. I REALLY need to talk with someone who knows how to do this right. These issues are specific to the SW4024, so the most helpful responses would be from those who have specific knowledge of the issues this presents. Thanks, Tim | ||
| Geoff (Geoff)
Registered Member Username: Geoff Post Number: 905 Registered: 12-2002 Posted From: 71.211.122.197 Rating: N/A |
Tim-- I am not an electrician either, but I have studied the situation and understand the discussion. The reason you are getting different answers is because the rules are slightly different for RV's than house electricans are used to dealing with. If you want a book on electrical systems and wiring for bus conversions get George Myers book-- it used to be available through a link on BNO although I can't find it now. Anyway, here is the skinny on neutral-ground bonding. Unlike a house, when you wire a bus for 120v all grounds go back to the circuit breaker panel-- you do not ground at the wall outlet boxes. You do not complete the neutral and ground bonding at the circuit breaker box. The only place you can make the neutral-ground bond is at the generator. When you add a shore line, the neutral-ground bond has to be at the shore line outlet box (where you plug in). So the transfer switch you need to make switches the neutral-ground bond from the generator to the shore line, as well as the hot leads. If you can't figure out how to wire the transfer switch, then hook up the generator output into a male plug which you remove manually and replace with the shore line hookup, in other words, a shore line with two male ends (yes, dangerous if you forget which side to unplug first). The warning you are getting not to bond the bus at all is in case the outside electrical box is wired wrong, and it does happen occassionally. The solution for that is to check the outlet with a meter to make sure it was wired right. As I write all this I am tempted to delete and stay out of it for two reasons-- like I said before, I am not an electrician so I might use the wrong terminolgy at time, but on the other hand I have a layman's understanding of electrical systems and can discuss the issue in laymans terms and not electrical geek-talk. The second reason I hestitate to post is that if you don't understand what is being discussed then you are not going to be able to do the wiring. I stongly suggest you get George Myer's book-- it is well written and explains wiring very well. --Geoff '82 RTS AZ | ||
| Richard Bowyer (Drivingmisslazy)
Registered Member Username: Drivingmisslazy Post Number: 1816 Registered: 1-2001 Posted From: 75.108.87.155 Rating: N/A |
(Quote) If you can't figure out how to wire the transfer switch, then hook up the generator output into a male plug which you remove manually and replace with the shore line hookup, in other words, a shore line with two male ends (yes, dangerous if you forget which side to unplug first). (end quote) Geoff, what about a female plug coming from the genset and a female plug coming from the shore cord. Then a male plug coming from the coach electrical box. Just move the male plug to whichever female plug is hot. Is that doing the same thing with no exposed male ends? Richard | ||
| Geoff (Geoff)
Registered Member Username: Geoff Post Number: 906 Registered: 12-2002 Posted From: 71.211.122.197 Rating: N/A |
Hi, Richard Yes, you could use female ends instead of male ends, but that has it's drawback also-- what you have then is an exposed male end coming from the hot side of the inverter that will be exposed. I don't like the idea of plugging and unplugging the generator lead/shore line ends anyway, but people do it. The DPDT switch I mentioned earlier in this thread works fine with the SW inverter, JimNH gave me the part numbers so I won't claim credit. --Geoff P.S. Tim: check this thread: http://www.busnut.com/bbs/messages/233/4194.html (Message edited by Geoff on January 31, 2007) | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 502 Registered: 1-2003 Posted From: 67.142.130.18 Rating: N/A |
George and Duane, Your assertion that it is somehow "safer" never to bond ground and neutral in a coach (emphasis yours) is patently ridiculous. It flies in the face of common sense, and is a dangerous statement (especially since newbies are probably following along). It's also against code, but, since you seem to have a particular disdain for the code, we can leave that part out of the discussion. Where you are correct is that one should never have multiple ground-to-neutral bonding points. That means that, when connected to a shore power system, there must not be a ground-to-neutral bond in the coach. However, if your coach has a generator, then there must be a ground-to-neutral bond associated with that generator. Moreover, if you have an inverter, then there must also be a ground-to-neutral bond associated with the inverter. The safety reasons for this requirement are simple and straightforward: If there is no path between the neutral and the ground wires in a system, then any hot-to-ground fault, such as from a wiring failure or accidental human contact with a hot wire, will not complete the circuit directly through the neutral system and allow the circuit breaker to trip. To state this more clearly, without the ground-to-neutral bond, you could literally connect hot to ground in your coach, thus energizing every metal surface in the coach, without tripping any breakers. I think you can see the potential hazards here. Now, when your coach is plugged in to shore power, the circuit will complete via the ground-to-neutral bond in the shore power system. But, when running disconnected from shore power (as on an on-board generator or inverter), the bond must be provided somewhere on board. The dilemma this presents for those converters who choose to include not only shore power but also a generator and/or an inverter, is how to ensure that one and only one bond is in place at any given moment, to prevent (as you put so well) energization of the coach frame as it carries part of the neutral return current. And that, I believe, is the subject of the original question. I'll get off my captain-code soap box now. -Sean http://OurOdyssey.US | ||
| Cameron Jones (Crazy71)
Registered Member Username: Crazy71 Post Number: 13 Registered: 12-2006 Posted From: 75.179.158.67 Rating: N/A |
(Quote) "To state this more clearly, without the ground-to-neutral bond, you could literally connect hot to ground in your coach, thus energizing every metal surface in the coach, without tripping any breakers." I do see your point here.... I have a question though... What if the ground to neutral bond is there, let's say on inverter power, and the neutral becomes broken...I am not sure if it would make a difference at a receptical or nearer the supply box....wouldn't the ground now be returning the voltage to the box ie. ground bar? So if the body of the bus is connected to the ground bar in the breaker box...wouldn't the body of bus have current flowing thru it and create a shock hazzard. Electricity takes the path of least resistance and there would be no reason for it to go thru you UNLESS maybe you were outside barefoot on wet ground...then the path of least resistance just might be through you into the ground... I only have an inverter in mine with no box at all. A male plug goes into inverter and goes to two wall outlets. I have no idea if they are grounded to bus body or not..the guy that had it before me and did that was more of a home handyman so I would bet if he wanted to ground them he would do it at the receptacle...but knowing how many people shortcut......it has plastic receptacle boxes so I bet the bare greound wire is on the receptacle terminal like it should be (for a house) but the box receptical is not touching metal anywhere...it really is not grounded anyway.... I guess the the neutral and ground are bonded in the inverter...The inverter is not case grounded. I have never pluged a GFI tester into it to see if it says it is wired correctly... This does get confusing as Confucious say. | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 503 Registered: 1-2003 Posted From: 67.142.130.47 Rating: N/A |
"What if the ground to neutral bond is there, let's say on inverter power, and the neutral becomes broken...I am not sure if it would make a difference at a receptical or nearer the supply box....wouldn't the ground now be returning the voltage to the box ie. ground bar? " No, under normal circumstances, no current should flow to ground. The ground wire (and grounded frames of appliances, etc.) is there as a safety measure, in the event of some kind of hot-to-frame short. The ground then returns the current safely, tripping a breaker in the process. A broken neutral wire in a branch circuit will effectively prevent any current from flowing in the circuit. The current will not simply detour to ground, since there should be no connection from the neutral side to the ground inside the appliances connected. In the "old days" (whatever you may construe those to be), certain appliances were miswired, deliberately or otherwise, so as to connect neutral and ground within the appliance, or, worse, to simply return what should be the neutral current through the ground. In locations where such a miswired appliance would present a dangerous shock hazard, the code now calls for GFCI receptacles or circuit breakers, which would trip immediately upon connection of such an appliance. Examples are anything outdoors, wet locations, all kitchen and bath outlets, etc. A simple three-light plug-in circuit tester will tell you if your receptacles are properly grounded. I recommend the style that also has a pushbutton to test GFCI circuits, which cost a few dollars more but will allow you to check your GFI protection even at a receptacle without a test button. Understanding grounding and electrical safety is critical to making a safe installation. That's why I bristle when I see "advice" in these forums that is not only misguided, but downright dangerous. (Of course, I probably would not have checked in to this thread at all, if not for the fact that it was driving traffic to my web site.) By the way, to answer the original poster's question, which I neglected to do in my last diatribe, you have basically two choices: The easiest, and most common way is to ignore the SW4024's internal transfer switch altogether. Use an external transfer switch which switches both hot and neutral. Wire the output of the transfer switch to the AC2 (generator) input of the SW4024, and set the transfer switch to default to shore power when neither is energized. Then connect a simple SPST, normally closed relay with a 120VAC coil so as to connect the ground and neutral lugs in the SW4024 together when de-energized. Connect the coil of this relay directly to the hot and neutral of your shore connection. This will "lift" the bond when connected to shore power. When your generator starts and the transfer switch throws, you will get the bond that is built into the generator. The second, more complicated way to do this is to use the internal transfer switch and an external, high-amp relay or contactor to disconnect both hot and neutral wires of the generator whenever shore power is connected. Then you will have the benefit of the built-in ground bond of the generator whether or not it is running, and no bond (and also no ability to use generator power) whenever shore is connected. A problem with both of these schemes that merits caution and careful attention is that choosing to use shore power itself to energize relays, either bond-lifting relays or generator-interrupting relays, may allow a hot-side-only failure of shore power, such as from the shore-side breaker tripping, to still leave ground and neutral bonded in the shore system, with a second bond inside the coach. As previously mentioned, this is a potential hazard, which is why I favor gating the shore input with its own contactor that will drop the neutral in the event of a hot failure. That being said, it is not common practice to do so, and the bond-relay sketches in the Trace SW manuals suffer from this deficiency. The relative complexity of my own scheme, referenced elsewhere in this thread, is more than you probably need for a three-wire, 120-VAC-only system, as I had the additional issues of a whole separate leg of power (additional hot wire) to contend with. That being said, you may benefit from my multiple-contactor approach to keeping inadvertent ground-neutral bonds at bay. -Sean http://OurOdyssey.US | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 73 Registered: 8-2006 Posted From: 207.231.81.154 Rating: N/A |
Sean, 1. I posted my qualifications for a reason. 2. I am on this site because I have a bus, and I am qualified to wire it. 3. I posted the NATIONAL ELECTRIC CODE SECTION ON RECREATIONAL VEHICLES AND PARKS FOR A REASON. 4. I CITED THE SPECIFIC CODE SECTION FOR A REASON. 5. Did you read, AND DO YOU UNDERSTAND THE NEC SECTION I POSTED? Now, I challenge you specifically to list YOUR VALID qualifications, the reason you said what you did, AND the NEC section(s) which you cite. (Please remember that you have to stay in section 551 which applies to RV's and RV Parks only! Sean, You say what I posted, (which is in the NEC section I posted) is "patently ridiculous," even though it is the NEC verbatim!!?? Please tell all of us why YOU think the NEC is patently ridiculous? Let me ask you this, even though Cameron already has! What happens when you bond grounds and neutrals together, and the neutral connection opens anywhere for any reason? The answer is that instead of the appliance just stopping working due to an open circuit, the neutral current now returns through the ground, (which is the entire bus)and as electricity follows the path of least resistance, it may be you or the person who took your advice and is holding on to a metal door while standing on damp ground, or connecting the potable water line, or dumping tanks! Your second post invalidates your first, your second post is the reason why you DON'T bond, you don't want neutral current flowing through the ground wire, which is what WILL happen if the two are bonded. I will not get into a further argument on this board, Sean's comment that what I have said is "PATENTLY RIDICULOUS" IS IN DIRECT CONTRAVENTION TO THE NATIONAL ELECTRIC CODE SECTION PERTAINING TO RV'S! I posted the entire section above, and it is Sean who is dangerously in error! Please do not think that my refusal to back off exactly what I posted and why is in ANY way an admission of error or omission on my part. I do not post to areas where I am not qualified, because I don't want anyone hurt by following incorrect advice! This is ugly, for which I apologize, but I need your attention. I will be MORE than happy to explain what and why off board to anyone who wants to ask! toddelec@psyber.com. DON'T BOND GROUNDS AND NEUTRALS TOGETHER IN A BUS ANYWHERE. Read section 551.30 which says: "Generators shall be mounted in such a manner as to be effectively bonded to the recreational vehicle chassis." Then read 551.32 Other Sources which reads: "Other sources of ac power, such as inverters, or motor generators... shall be listed for use in RV's... Other sources of ac power shall be wired in full conformity with the requirements in Parts I, III, IV, V, and VI of this article..." (Ground/neutral bonding is in article V!) The question about what to do with the fixed ground/neutral bond in a generator has a simple code-supported answer. Treat it like the bond mentioned in Section 551.54 (C) dealing with clothes dryers, and electric ranges using a grounded neutral conductor, "shall be removed and discarded." George M. Todd, Owner, Todd Electromechanical, Calif. Contractors License #624299, Classes C10, & C20, issued August 6, 1991. Calif. also requires 4 years VERIFIABLE experience before granting eligibility to take the test. | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 504 Registered: 1-2003 Posted From: 67.142.130.22 Rating: N/A |
George, First, let me apologize for a poor and probably offensive choice of words when I wrote "patently ridiculous." It was uncalled for -- I think I was reacting mostly to Duane's statement: "...To hell with code...". As you know, almost every provision of the code is built upon one or more deaths or serious accidents. You have me at a loss, though, because I no longer have a copy of the code, so citing chapter and verse isn't easy (I live in a bus... the giant NEC Handbook was one of the things that had to go...). That being said, I remember a good deal of it from designing my bus, and also from having to deal with it routinely across a long career of designing large-scale electrical distribution systems. The other reason you have me at a loss is that quite a few key changes were made to section 551 in the 2002 code, and the last code I had (or had to work with) was the 1999 code. For example, detail on generators was moved into 551 in that code, whereas "vehicle mounted generators" were covered in a different section in prior years. However, you state that I "have to stay in section 551 which applies to RV's and RV Parks only!" which, as you must know, is incorrect. 551 is not intended to be all-encompassing; it is intended to supplement, clarify, and in some cases over-ride the specifics embodied in the remainder of the code. For example, details on ampacity of wire types is not covered in 551 -- it is expected that you will follow the ampacity rules defined elsewhere. Wiring methods not specifically covered in 551 are expected to conform to 300, etc. In particular, the rather lengthy section on grounding methods is still applicable to RV's, with only a handful of exceptions which are spelled out in 551. I'm sorry I can't cite the relevant code sections here, because I don't have the code in front of me, but I am willing to state unequivocally that any "separately derived source," as that term is defined in the code (and understood by engineers) must have a single point of ground-to-neutral bonding. Without it, direct-fault circuit interruption simply will not work. As long as your RV is connected to shore power, then any on-board inverters or generators are not separately derived sources, and, as you wrote, must not include a bond. That all changes the instant you unplug that shore cable. Now, if you have a generator running aboard your RV, it is the sole source of power and there must be a ground/neutral bond at the generator. Likewise for an inverter. 551.54 does not contemplate or cover inverters as separately derived sources. We are in violent agreement about the reasons for not bonding inappropriately -- there should never, ever be more than one bonding point, which is normally in the shore system. But there also should never be less than one bonding point, or there will be no way for fault current to trip breakers. I should point out here that the sort of automatically removable bond we are talking about is to be implemented at the inverter, or source of power, not at the end of the branch circuit or in the appliance or subpanel (as described in 551.54) so your statement that "...instead of the appliance just stopping working due to an open circuit, the neutral current now returns through the ground" does not apply, as the open neutral means there is no path for the current to reach the bonding point and be carried to ground. Many (perhaps most, nowadays) inverters specifically listed for RV use include the automatic ground-neutral bond within the inverter itself. This issue only arises when using an older (but still listed) inverter such as the SW4024, which must be bonded externally as explicitly stated on page 27 (covering listed RV installations) of the manufacturer's installation and operations manual for the product. If I can get to a copy of the code before this discussion withers, I will post the relevant cite. Or perhaps someone else here who has a copy can do so -- I know there are several here who have been through this before. -Sean | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 74 Registered: 8-2006 Posted From: 207.231.81.154 Rating: N/A |
Sean, I have just sent you a big e-mail, and after reading this post, I want to apologize for some of the things said. That said, I would like to take you to task over "open circuit, and appliance not working, and no path for current to reach the bonding point..." This depends on where the failure is. If the failure occurs between the appliance and the panel, all is well, the appliance will just stop. If the bus IS bonded, and the fault occurs in the power cord, shore receptacle, or a switching relay, etc., neutral current will return through the ground, nobody knows an open neutral has occurred, which is dangerous. No bonds equal a dead appliance, which is just what is supposed to happen. Then you just go hunt the failure without incident. The differernce of potential IS the same from hot to neutral and from hot to ground, consequently, a hot/ground fault will trip the breaker, as the fault current (which is all a ground is supposed to carry) goes back to the ground bond on the equipment supplying power. Section 551.30 Generator Installations (A) Mounting says "Generators shall be mounted in such a manner as to be effectively bonded to the recreational vehicle chassis." This is where the fault current goes in a hot to ground fault. A generator ground and neutral are not always exactly the same. We must also be aware that a GFCI must trip at a maximum of 7 milliamps (.007amp) A bonded panel will let a LITTLE neutral current flow back on the ground wire, causing all sorts of nuisance trips. I had better post this before you get mine read! G | ||
| Tim James (Tjames)
Registered Member Username: Tjames Post Number: 19 Registered: 8-2006 Posted From: 66.59.118.229 Rating: N/A |
George, I believe you're missing the point that whenever shore power or generator power is connected the ground to neutral bond in the bus panel must be broken. I am aware of this and stated this earlier. I'm not suggesting that the bond remain in the bus panel when connected to shore power. However, if there is no bond when not plugged in or on generator, but when deriving power solely from the inverter, then how would a hot wire short to the bus chassis trip the breaker???? It wouldn't. The entire bus would be hot! This whole post is supposed to be about the best way to accomplish this automatic switching of the ground to neutral bonding so that it always exists in one and only one place. | ||
| Duane Kaler (Duane)
Registered Member Username: Duane Post Number: 23 Registered: 5-2006 Posted From: 69.19.14.24 Rating: N/A |
Hi Tim I have learned a lot following this topic and that is a good thing because I was previously misinformed. As I understand it you are referring to the ground to neutral bond in the bus panel. That should not be there, ever. When there is no shore or gen set power then your power is coming from your inverter and that is where the bond needs to be, not in the bus panel. Page 27 in your SW4024 installation manual shows this very well. Recently educated, Duane | ||
| Cameron Jones (Crazy71)
Registered Member Username: Crazy71 Post Number: 14 Registered: 12-2006 Posted From: 75.179.158.67 Rating: N/A |
I think George is saying that the bond should not be IN the bus. It can be common to want to wire it like a house...which would be bonding the neutral and ground in the bus panel. As Duane stated above "referring to the ground to neutral bond in the bus panel. That should not be there, ever." I think this is what George is insistant on. The one place that the bond would occur on shore power is somewhere before the shore power plug you plug into. I can grasp this and agree pretty easily. And I think this is the same result that Sean calls for WHEN on shore power AFTER the switching apparatus does its job and switches hot AND neutral. Now I am still confused about gen and maybe inverter power. If I have an inverter and know nothing about the insides of it....whether it has bonding inside or not without ohming it out..... If it does not and I hook it up..will the appliances even run? I think it depends on if the receptacles are grounded to the body of bus and possibly inverter to....and possibly dependent on the boning in the inverter too. Yes, I said I was confused here. Gen is about the same I think. I think most gens have the neutral and ground bonded. This should make the case/frame of gen ground and same as neutral. Is this ok if only a gen is used? If it is never plugged into shore or even set up to do so? Or should the gen's neutral to ground connection be separated and the neutral would be the only path other than hot... Ground not hooked to anything. This is how many receptacles in old houses are wired...not GFI, not up to current code, but two prong, two wire 15 amp recepticles have run things for years. Now back to George's idea. If you wire with the two wires, with no ground like I just mentioned...and the neutral breaks anywhere, the appliance stops running... Since you are on a bus insulated from the ground and the body is not connected to anything.... If you Grabbed the hot wire to the appliance, you are not really giving the voltage anywhere to go. If the bus is grounded by the third ground wire going to the same spot in the gen the neutral goes to....the hot could be returning through the ground and the body of bus could have voltage going through it and could shock you if you were outside touching door or body...giving it a path from body to earth. Now this would only occur is a GFI was not used I believe... If a GFI was installed in the appliance circuit I described above....when the neutral broke, wouldn't the GFI immediately trip as the voltage tried to return to complete the path on the ground wire??? If it would, then it seems safe with a GFI receptical in each circuit. I know I would not want a Main GFI at a box or anything.....GFI can be touchy and I would rather just have to reset one circuit than to have eveything shut off. | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 508 Registered: 1-2003 Posted From: 67.142.130.27 Rating: N/A |
"If I have an inverter and know nothing about the insides of it....whether it has bonding inside or not without ohming it out....." Most modern hard-wired inverters made for the RV market have an internal relay that bonds ground and neutral whenever there is no AC input power to the unit. The Trace SW series is a notable exception (having been designed initially for fixed use in renewable energy applications, not RV use), and was the issue that started this thread. If you tell me what make and model of inverter you have (or are contemplating) I can probably tell you if it implements the automatic bonding/unbonding internally. And just to be clear, no one on this thread has suggested that it is appropriate to bond ground and neutral to each other permanently inside of a panelboard --the temporary, automatic bond we are talking about is to be implemented AT the inverter, meaning as close as possible to it if it is not internal to the unit. -Sean | ||
| Cameron Jones (Crazy71)
Registered Member Username: Crazy71 Post Number: 15 Registered: 12-2006 Posted From: 75.179.158.67 Rating: N/A |
Sean, I am way below qualifying as having a hard wired inverter. My bus isn't actually wired. I simply have a Tripp-Lite 1000 or 1200 watt that has two outlets on it to plug a cord into. When I bought the bus the inverter had one of the outlets going to a piece of romex that supplies two standard household receptacles. The main problem I see in this is in many situations it would be easy to overload the inverter with room for 4 plugs drawing on one outlet plus whatever the other inverter outlet may be powering. In my situation, overload has not been an issue. I might as well remove the second outlet as I have never used it. The other one has been used for a vacuum cleaner a few times. They are unused most all of the time. I just leave them there in case I have to plug a cell phone charge in. The other outlet on the inverter powers a 13 inch tv and a cd player and about 6 miniature bulbs. Most of the lighting is 24v coach. The 6 are on a switch so I can have enough light if the bus is not running. There were a couple of mentions of the neutral to ground bond being in the bus panel. This is where I might have gotten some confusion. Tjames 2nd post and George's reply and Tjames last post I think were referring to this by "bus panel". I assumed they were referring to the electric box like in a house and being wired similar. In a house the neutral and grounds are bonded in the box. And I believe this thread has come to the conclusion that in a BUS we DO NOT connect the two INSIDE of the PANEL BOX. Have I got it straight now? | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 509 Registered: 1-2003 Posted From: 67.142.130.43 Rating: N/A |
Cameron, With regard to overloading your inverter, my guess is that the unit has built-in protection against that (check your manual). What you've done by adding outlets is not fundamentally different than, say, plugging one of those 8-outlet power strips into it. With regard to the "bus panel" question... I hate to give unequivocal answers to these kinds of questions, because the subject is more complex than that. If what you mean by "bus panel" is a panel board upstream of the inverter and fed directly by the shore cord, or by a transfer switch that can provide a direct connection to the shore cord, then, yes -- ground and neutral should NOT be bonded in this panel. That being said, the relay we have been talking about needs to go somewhere. The diagram on page 3-27 of the Trace manual does not show it, but all wiring to and from the relay needs to be physically protected in the same manner as other AC power wiring, and, more importantly, per the NEC and safe practice, the ground and neutral for any circuit or system must, at all times, travel with the other (hot) conductors of that system. This is why, for example, when installing a light switch in a house, you can not simply open the hot leg, run the hot over to a switch someplace and back, and get away with only two wires in your switch wiring -- you must run all three wires, Hot, Neutral, and Ground over to the switch and back, even though the switch itself will interrupt only the Hot. In the same way, the ground/neutral bond relay shown in the SW series manuals must be installed in an enclosure that is in-line with, and includes all of, either the input supply wiring to the unit, or the output wiring from the unit. Since many installers will use conventional metal panel boards or load centers as either main panels (between shore/generator/ATS wiring and the inverter) or inverter subpanels (downstream of the inverter to feed inverter-only loads), these already protected and already in-line enclosures make handy places to install the relay, provided that there is a safe amount of extra room in the enclosure. Another possible location for the relay would be in the enclosure for the ATS, again if there is room. It's safest and "best" to install a completely separate NEMA enclosure for the relay in-line just upstream of the inverter, but, as you well know, installing all this stuff in the sometimes cramped quarters of a coach can be challenging, and there may simply be no room for a separate enclosure. If the relay is installed in the "main" panel (the one upstream of the inverter), what you would see in that panel is a conventional ground bar, bonded to the enclosure, and a separate, isolated neutral bar, mounted on insulated stand-offs. The load terminals of the bonding relay would be connected to these two bars, thus connecting (bonding) them together when only the inverter is running, with no external source of power. Before anyone jumps in here to tell me that it's best to bond ground and neutral downstream of the inverter so that upstream circuits remain unbonded, I want to point out that the SW series inverters do not switch their neutrals (input and output neutrals are tied together inside the case), so it does not matter whether the bonding relay is upstream or downstream: when the relay makes the bond, everything both upstream and downstream of the inverter, at least as far upstream as the neutral-switching transfer switch, if any, will see the bond. I hope this makes sense... -Sean | ||
| Len Silva (Lsilva)
Registered Member Username: Lsilva Post Number: 83 Registered: 12-2000 Posted From: 71.30.246.203 Rating: N/A |
Just to add to the discussion (which has been going on for about ten years now), my PowerTech 7.8KW generator, 1994 vintage, definitely has the neutral bonded at the generator. It is lifted at the transfer switch. Len | ||
| Nick Badame Refrigeration Co. (Dnick85)
Registered Member Username: Dnick85 Post Number: 88 Registered: 2-2006 Posted From: 68.45.178.44 Rating: |
George and Sean, All theese posts prompted me to recheck all my wireing in my bus. In doing so, I'm glad to report that all my nutrals are isolated from my grounds. George, The nec code makes perfect sence! Thanks. Nick- | ||
| Chris Peters (Chris_85_rts)
Registered Member Username: Chris_85_rts Post Number: 5 Registered: 11-2006 Posted From: 66.194.150.45 Rating: N/A |
Nick, what brand and model of Genset do you have that does not tie Neutral and Ground inside? For example, my PowerTech 8KW Genset, only had wires for two hots and one neutral/ground. The neutral of the genset was connected to the chassis of the genset and you are specifically told to connect the genset chassis to the bus chassis. From what I've read here, the only time you'd have a neutral/ground bond is when you were plugged into shore power. That seems to contradict everything I've read in the past on this subject. Great. | ||
| Richard Bowyer (Drivingmisslazy)
Registered Member Username: Drivingmisslazy Post Number: 1823 Registered: 1-2001 Posted From: 75.108.87.29 Rating: N/A |
Nick, did you go inside the actual genset internal connection box? That is where the neutral/ground connection is made. You could still have a separate neutral and ground wire coming out of the box, but all manufacturers make the internal connection. It is possible that someone has removed it however. Richard | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 518 Registered: 1-2003 Posted From: 67.142.130.36 Rating: N/A |
The issue of neutral/ground bonding within a generator set is a tricky one. The vast majority of off-the-shelf generators ship from the factory with neutral and ground tied together. In most cases, the bond is in a junction or wiring box attached to the generator head, and this is certainly true for any generator that has multiple wiring configuration possibilities. (By multpile wiring configurations, I mean either the simple choice between 240-volt output versus 120-volt output, or the more complex choice between three-phase output and single-phase output.) There are a handful of generator heads where the internal bond is not easily removable, because it is implemented within the stator (as opposed to a convenient junction box). In any case, in most vehicle applications, the ground and neutral are bonded within the generator, and, further, the code requires the generator frame also be bonded to the vehicle frame. If an on-board generator is the sole source of power (i.e., no shore cord input exists), this presents no problems. Examples are contractor work trucks, phone company pole trucks, and the like. In a coach application, the simple way to handle the "removal" of this bond when on shore power is to use a transfer switch that switches the neutral along with the hot(s). In this case, the ground/neutral bond still exists inside the generator, but the neutral system throughout the rest of the coach is disconnected from it. (Instead, it is connected to the shore line, where it will be bonded to ground on shore.) Note that in 99% of coach applications, this is standard fare, works flawlessly, and is not a problem. That being said, if you have a Trace SW series inverter-charger, you have a dilemma: you can ignore the internal transfer switch inside the unit (which does not switch the neutral), and implement a proper, neutral-switching transfer switch externally, thus utilizing only one of the two AC inputs on the inverter (usually the AC2 input). This is how many converters elect to do it, and it's how Dick Wright advises it be done in his seminars and in his printed recommendations. If you're hell-bent on making use of the internal transfer switch in an SW series box (as I was), then you have an engineering problem ahead of you. You can implement various kinds of external disconnects that switch around based on external factors (monitoring for presence of shore cord, for example, and using that factor to externally disconnect the generator from the AC2 input). Or you can open up the inverter, thus both voiding its warranty and also invalidating its UL listing, find the DC signal that operates the internal, single-pole transfer switch, and use that signal to control an external relay to do what you want. The method I chose was to remove the neutral/ground bond from my generator, and connect the generator to the AC2 input full-time. I had to build my own custom ATS, which includes the ground/neutral bonding relay, to manage both the safety disconnect of the shore system whenever shore power is not energized, and the switching of the second leg of the 240-volt power (since the SW4024 uses only one of the two). It was a colossal PITA but I'm happy with the result. I can not recommend this, though, for the faint of heart, or the electrically challenged. My advice to the average Joe is to get a more modern inverter that does all the right things internally and just plain works. To someone who absolutely wants a Trace SW but does not want the heartache, I say get a quality 50-amp, three-wire transfer switch and just use the AC2 input on the inverter. If neither of these appeals to you, then you need to do the engineering work, and it's imperative that you have the proper understanding of the concepts ahead of time. FWIW. -Sean | ||
| niles steckbauer (Niles500)
Registered Member Username: Niles500 Post Number: 699 Registered: 11-2004 Posted From: 24.129.157.205 Rating: N/A |
For those of us that are not as technically savy as Sean the easiest and safest way to deal with the nuetral/ground bond is through a transfer switch as stated by Sean - mine is a 240VAC 70 amp 4 pole switch with automatic indicator lights which also tell me if I have either reversed polarity or an open ground/nuetral at my shore source - not necessarily the cheapest way, but well worth the $$$$$ IMHO - the system is idiot proof (as I are one) - Example; http://www.rvpowerhouse.com/product.php?id=181&USER_SID=a38b630adc81703cd57e8588085dfbb2 | ||
| Cameron Jones (Crazy71)
Registered Member Username: Crazy71 Post Number: 16 Registered: 12-2006 Posted From: 75.179.158.67 Rating: N/A |
Can you also do it the old fashioned mechanical way? Have your shore power cord that must be plugged in manually to the gen when you want gen power...If you do this can't you leave the gen boned inside since you will only have one source of power and bonded in one place when the cord is plugged into gen. I think someone mentioned this earlier with having male ended cords or something...It would need to be safe... But will this manual means work...?? | ||
| Chris Peters (Chris_85_rts)
Registered Member Username: Chris_85_rts Post Number: 7 Registered: 11-2006 Posted From: 66.194.150.45 Rating: N/A |
Cameron, this is how I do it. My shore cord plugs into either the shore recepticle or a genset recepticle located in the shore cord storage compartment. No chance of exposed power. | ||
| Cameron Jones (Crazy71)
Registered Member Username: Crazy71 Post Number: 17 Registered: 12-2006 Posted From: 75.179.158.67 Rating: N/A |
If I ever get around to setting mine up I will probably do it this way also. I'm sure many people get tired of doing it manually. I know I do get tired of going back there to turn on and off the manual heat valve. In those temps that are just in between. Some times you need air in th day, and heat at night...I still use the factory heat and ac. Iam sure just haven't looked yet...BTW MCI 8. | ||
| Don Evans (Doninwa)
Registered Member Username: Doninwa Post Number: 5 Registered: 1-2007 Posted From: 65.61.96.82 Rating: N/A |
Our old bus has a manual system too. There is a male pigtail from the panel that either plugs into the female generator plug or the female plug on the coach end of the shore cord. Simple/cheap. No inverter in the old rig. You have to be there anyway to plug/unplug/store the shore cord. No hot exposed conductors. Simple to deal with the bonding too. Could be set up with just a switch and hard wired for a few more $$$$. I always plug the pigtail into the generator when I disconnect the shore cord so its ready anytime to fire up the generator if needed. Mostly to run the air when on the road. Is there a reason that I would want to run the generator when hooked up to shore power? Not so far. I suppose if I had 3 airs and only a 15 amp hookup. Would not what to annoy the neighbors anyway. The old Onan is not what you would call quiet! If I use a SW type inverter in the new rig with the power supplement option the generator should not be needed when plugged in either. What am I missing? Something obvious no doubt! | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 522 Registered: 1-2003 Posted From: 67.142.130.41 Rating: N/A |
The manual plug-and-receptacle system works fine and can be installed according to code. In this case, the ground-neutral bond needs to be in place inside the generator enclosure, so that, when you plug the cord in to the generator receptacle, you have a bonded system. When connecting to shore power, the bond will be found there. None of which addresses the matter of an inverter, which was the original topic of this thread. The inverter will still need to have a means to make the bond when neither shore nor generator is connected. Most inverters now on the market will do this automatically, but the SW series will not. A further complication exists when using the plug-and-cord method. To wit: both the recommended bonding-relay wiring for the SW series, and the internal bonding mechanisms of other inverters, work by detecting the presence of power on the input line. If you have an inverter, and a cord-connected generator, then the possibility exists that you will leave the cord plugged in to the generator, which has an internal bond, yet the generator may not be running. In this case, the inverter will also make a bond (since it does not detect input power), and now you have a system with not one, but two bonds in different places. That will cause at least some of the neutral return current to flow through the ground system, which will include the coach frame. This could be dangerous. For this reason, I recommend against using a cord-and-plug setup if a hard-wired inverter/charger will also be part of your system. Incidentally, this double-bond situation can also arise when connected to a shore power system, where the shore breaker is turned off or tripped. The ground and neutral will still be connected (circuit breakers interrupt only the hot wire), yet your inverter will not detect input power and will also make a bond inside the coach. Now the possibility exists that current will flow through the coach frame and into the shore ground, which could be dangerous and even fatal to someone standing outside and touching the coach. For this reason, I recommend, no matter what else is done, to have a self-holding contactor between the shore cord inlet and the rest of your system. This contactor would carry the hot(s) AND neutral into the coach. If the hot wire fails (for example due to the shore breaker tripping), then the contactor will release and the neutral will also be interrupted, thus preventing the double-bond scenario. -Sean | ||
| Don Evans (Doninwa)
Registered Member Username: Doninwa Post Number: 6 Registered: 1-2007 Posted From: 65.61.96.82 Rating: N/A |
Sean, I think I understand what is required, just not sure how to keep it simple. If I follow your post, does this sound close to a workable plan? Connect the neutral and ground through a contactor only and never anywhere else in the coach. Generator hard wired to inverter second input. The neutral would be switched by the same contactor between the inverter and shore power such that the neutral is bonded to ground when there is no power from the shore cord and disconnected when shore power is present. The current to energize the contactor would be from shore power. The neutral to ground bond line would be normally closed and open on shore power. If shore power failed the bond in the coach would be connected but so would the shore bond. The chassis should be held at or near ground potential by the shore bond. Don't know if the neutral is opened by the inverter when it is supplying AC from batts. If it is can it be connected from inverter output back to ground thru contactor to keep the bond? Contactor would be 4 pole, switching the two hots and the neutral from the shore cord and the 4th contact would be the neutral to ground bond. Ground from shore would not be switched and connected directly to ground bus in breaker panel. Boy I wish there was a simple way to draw a schematic to post. (Message edited by doninwa on February 08, 2007) (Message edited by doninwa on February 08, 2007) | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 524 Registered: 1-2003 Posted From: 67.45.244.133 Rating: N/A |
Don, I'm not sure I follow this. Also, you don't mention what type of inverter you have. What I think you are asking is if you can have a transfer switch to transfer between generator and shore, with generator being the "normal" or "resting" state of the switch. The coach would then benefit from the ground-neutral bond in the generator whenever shore is not connected. If that's the question, then the answer is yes: the ground-neutral bond in the generator, in this type of setup, will suffice for the inverter as well. However, if you have a Trace SW series, the switch just described would be entirely external to it, and would mean that you would just use one input to the inverter, and make no use of the internal transfer switch. Also, to further clarify what does or does not get switched: If a neutral is switched, the corresponding hot(s) must also be switched along with the neutral. Grounds are never switched. The inverter should not lift the bond when inverting -- only on presence of a shore connection. And, lastly, a bond in the coach while the shore is connected is precisely the dangerous condition we are trying to avoid. It will guarantee that some of the neutral return current to the shore system will be traveling through the bus chassis. -Sean | ||
| Don Evans (Doninwa)
Registered Member Username: Doninwa Post Number: 7 Registered: 1-2007 Posted From: 65.61.96.82 Rating: N/A |
This is what I meant. Trace SW inverter. Generator hooked directly to SW Gen inputs. No bond in Gen or inverter. Coach neutral to ground bond only thru normally closed contacts in a contactor. Shore power hot connection would activate contactor and open coach bond. Contactor could open/close shore hot and neutral. (Probably not needed because inverter opens them when no shore power.) Don't see how having the shore ground when the shore hot is open due do breaker tripping or whatever could cause problems. If there is no shore hot the shore neutral should also be opened by the inverter. That simply leaves the chassis grounded through the shore ground with no return path to the hot sources in the coach which is either the inverter or gen. Besides, if you can't run the ground through contacts how could you avoid this condition if the shore breaker trips? | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 531 Registered: 1-2003 Posted From: 67.45.244.133 Rating: N/A |
"If there is no shore hot the shore neutral should also be opened by the inverter." Umm, this has been said several times now: the Trace SW series DOES NOT switch the neutral, only the hot. This is the crux of the problem, and the reason why, in an RV, you can not simply use the built-in transfer switch in an SW inverter. You MUST have an external contactor or relay to break the shore and/or generator connections as appropriate. "...if you can't run the ground through contacts how could you avoid this condition if the shore breaker trips?" Simple: you run both hot(s) and neutral of the shore line through a contactor that releases whenever shore is not hot. Then, even though the ground is continuous to shore, the neutral is not connected to anything in the coach. Make sense? -Sean |
