| Author | Message | ||
| Tom Dessert (Mci5er)
Rating: N/A |
Got shocked laying under the bus yesterday. So I took the ole Fluke Digital voltmeter, set it for 200VAC jammed the negative in the moist dirt next to the bus and hit the skin with the positive. Read 22.2vac, I unplugged shore power and it's gone. I checked service power at the pole everything was normal. Killed all the 110 Breakers in the bus with exception of inverter and IOTA transfer switch. The inverter was humming so out of curiousity read the (+) side of the batteries to earth ground 22.2vac, which varied in amplitude along with the hum i.e.( no hum ac voltage 1.0, hum gets louder voltage climbs according to the 22.2ac then falls). While in the battery compartment(house) I noticed that the chassis ground from the inverter was grounded to the bus chassis. Maybe it's old age or total lack of understanding but shouldn't the earth ground from the service power be common to all of the 110 circuit and not connected to chassis ground ? It seems from looking at my setup that both ac and dc are sharing the common ground of the chassis. Any help appreciated. Thanks Tom | ||
| Greg Peterson Rating: N/A |
Normally in an AC system the earth ground is connected to the metal box or in your case the bus frame and chassis. When you plug into AC outlet the bus should be connected to the green or earth ground wire at the ac outlet. The green or AC ground should be connected to earth by a copper rod driven into the earth. The connection from neutral to this earth ground is to be made at the AC outlet point and not in your bus. This system is what UL would call a grounded dead metal system. If a Hot line wire should short to the chassis of your bus it would immediately blow the circuit breaker and there would be no harm or shock hazard. If you did not ground the bus chassis UL would call this ungrounded dead metal and you would have to put signs on the bus that says warning shock hazard. A problem can occur if the outlet was improperly wired such that neutral is connected to the hot side of the line and earth ground is not actually connected. In this case the whole bus frame would be hot with respect to real earth ground. It sounds like your bus frame is not being connected to earth ground in your AC outlet or your AC outlet does not really have a earth ground in it (open or broke). If it were there you would not measure the voltage you are getting to earth ground. You must also have a big leakage problem probably in your inverter that is raising your frame potential above earth. There are capacitors and MOV or surge suppressors in the inverter to protect it from line surge and to reduce EMI noise. If one of these is leaking then you might get current to earth ground. The MOV is suspect because after many surges they can short out. I have seen these things then catch fire. If you had a real earth ground the breaker to the inverter should trip out because of the fault. Hard to tell from your description but I would check your AC outlet for real earth ground and proper connection of L1, L2, neutral and ground. Just some ideas hope it helps Good luck and remember use only one hand and rubber shoes are good to. | ||
| John MC9 Rating: N/A |
Re: "The connection from neutral to this earth ground is to be made at the AC outlet point and not in your bus. " Ohh-ohh.. The tie of the neutral and ground is to be made at the source of supply. At the genset Or at the inverter Or at the power pole. The three cannot be combined, nor can they be shared. If the supply is coming from the genset, the ground and neutral must be tied at the genset. If the supply is at the power pole, the tie must be at the power pole. You cannot, or should not, tie the ground and neutral arbitrarily. (only at the single source) The inverter is tricky, since it can be powered by the batteries, the genset, or the power pole. Read the docs for the inverter. Heavy duty condoms on the fingers, apply. | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
First and foremost, if your shore power hookup was "normal", you should have an intact ground coming thru it, hooked to the chassis of your bus. That in itself would have made your shock virtually impossible. So I'd look for a few things: (1) make sure your ground is actually intact electrically, all the way from the power plug to the coach chassis. (2) If (1) checks out, I'd start looking at your power source from the "pole" all the way back to the building's utility service drop/entrance point, and make sure it's intact and properly grounded to earth at the main service ntrance panel. It pretty much has to be one or the other... either the ground circuit you think is good in your bus isn't, or your pole power isn't grounded back at the service drop (water pipe, copper rod pounded into the earth, etc), or the ground from the service drop to your pole is not intact...or you've got some wires mixed up somewhere... My other suggestion is to check all this out with a fairly heavy handed approach. It's not enough to just do a visual. In situations like this, I like to take a 100 watt lightbulb, hook one side to 120 volts and use a long wire on the other side as a "probe" to test ground integrety. You simply probe what you think should be earth ground, and if it's Ok the bulb will light up fully. If it's not ok, you'll get a dim bulb or nothing at all... there's the beginning of finding that bad ground... Note- this is somewhat dangerous so be careful. But personally, I like to see that the ground is really solid and this is the only way I've ever figured out how to do it. I concocted the idea back in '74 when I shocked the crap out of myself in a friend's shower (100 year old house, plastic tub, turned out due to an old wiring system and a bad ground, there was 60 volts between the water valves and the drain cover. Ouch... good way to check out in a hurry, all wet and such) I couldn't find the problem until I finally did this probe thing... found out that house's ground was hooked to some old galvinized water pipes that had been long disconnected and replaced with copper- that along with a faulty washing machine that was shoving a lot of power into what was left of "ground"... what a mess... and what an ouch!!! ...and... 120 volts should be grounded to the bus chassis, 12 or 24 volts of your bus batteries should be grounded to the chassis, and your house batteries should be grounded to the chassis. FWIW... Last, 20 volts AC is not enough to shock. It takes around 40 unless you're all sweaty wet with salt and the dirt you're laying in is wet... There must be something else going on although the 20 volts shouldn't be there.... Hope you find it! Please report in.... | ||
| JW Smythe (Jwsmythe)
Rating: N/A |
Tom, I won't argue the grounding issue, it's apparent that you have one. Greg and John already gave you the long answer on what to look for. Are you sure on that 22VAC? Switch over to DC, and see what it shows. From what I've always been taught, it takes somewhere closer to 90V to beat the resistance of your body. Lower currents will hurt, if you lower the resistance, such as piercing your skin, or doing the old favorite of sticking your tongue to a 9V battery (the tongue is a better conductor than skin). If you happened to have a cut, and that was exposed to the moist ground, that could have lowered your resistance. I found this out the hard way. A phone line ON the hook is 48VDC. A phone line OFF the hook is 3VDC to 9VDC. A phone ringing is 90VAC (20Hz). That 90VAC 20Hz what made the old phone bells ring. The ring itself was made from the frequency of the AC current supplied by the phone company. Modern phones only detect the voltage, and do whatever fancy ring it wants to. I was working on live phone lines, as I had done many times before, and didn't have any concerns. Then someone called, and I happened to be touching the bare wires, and standing on moist ground. Needless to say, I wasn't very happy. I'll avoid telling of being zapped with 15KV and 30KV. I'll just say, it's not fun. It's ok to laugh about now, but I'm very careful not to let it happen any more. And... as I've also always been taught, never be the better ground. And, keep one hand behind your back. You don't want any current passing through your heart. Low currents, like 90V through the skin, or much less if your skin is pierced by a sharp wire, can easily stop your heart. | ||
| Brian Brown (Blue_velvet)
Rating: N/A |
Great suggestions, folks. I'm no electrician, but just wanted to clarify Gary's light bulb probe (which is an idea I've actually used before, too). Anyways, the one lead of the lightbulb has to be hooked up to the hot (black) leg of 120VAC to get the light bulb to come on when touching a valid ground. Right? I suppose if the neutral (white) leg lit the bulb up when touching the other to ground, you've got even more problems! bb | ||
| Brian Brown (Blue_velvet)
Rating: N/A |
Oh! On the measured voltage issue (22VAC), I have a modified sine inverter and its output reads low on the AC readout on my multimeter... something about it not being a true RMS meter. So, Tom could very well have more voltage leaking than he's reading with his meter if it's the inverter leaking and if it's a mod-sine inverter and if he doesn't have a true RMS meter. Clear as mud? bb | ||
| herman Rating: N/A |
As Gary has pointed out, you do not have a solid connection between your ground network and actual earth ground. I would add that, the worse the connection, the less leakage current from the nominal current carrying conductors is required to elevate the ground network by a given voltage. So, once you get the ground taken care of, then you need to find your other problem, i.e. the low grade fault onto the ground network. This too may be either in the bus or upstream of the shore connector. A ground fault circuit interrupting (GFCI) breaker placed at the shore connector is a good way/place to start looking. John MC9 has best expressed the neutral-ground bonding requirements: there must always be one and only one bond in effect, and the active bond must be located at the power source that is currently supplying the bus. Again, that means at the genset, or the inverter, or, in the case of shore power, either at, or upstream of, the shore receptacle. Techniques for meeting this requirement include, for transfer switches, switching neutral along with the hot(s); relays can also be used to make / break bonds. | ||
| Tom Dessert (Mci5er)
Rating: N/A |
Guy, a little more info on this for yeah. At the time I got shocked it was a beautiful Southern Oregon day about mid 80's. I was in a tank top covered with sweat, laying on bare ground wet from washing the bus. I rolled over and lightly touch my shoulder to the underside of the bus. I thought I hit a sharp edge or something. Didn't think more about it at the time. Shortly after, a friend came over and climbed under to see what I was up to. He got a quick zap, that caused him to spill his beer. That's when I figured I'd better check this out. As far as the comment about the pole receptical (30A) looked "normal". I unplugged my (50A) service cord from the plug drove a 4' grounding rod in next to it thinking that the ground in my sub-panel might be the problem. I didn't connect the grounding rod at the time, I took resistance readings from the rod to the ground pin on the receptical (dead short highest range), likewise with neutral. I also took voltage reads from neutral to hot and ground to hot 124V as I recall. I also cleaned the service power cable connector until it shined like new. Finally my inverter is a Freedom 20D and as I recall from the installation guide it says that the inverter chassis ground should not be connected to battery ground but returned to the source of supply which in my case was the IOTA transfer Switch. This switch has seperate buses for neutral and ground. So from my power cable the white goes to neutral in the switch and ground goes to the ground bus. The ground bus is tied to the bus frame. Well this is getting confusing. I think I'll setup and do the bulb test tomorrow and see what I can find. | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
Hi Guys, Yes, "one lead of the lightbulb has to be hooked up to the hot (black) leg of 120VAC to get the light bulb to come on when touching a valid ground." and absolutely, "If the neutral (white) leg lit the bulb up when touching the other to ground, you've got even more problems!" Happily, almost everything everyone has to say above is valid!! Wheeeee, good posts guys!!! It may be that you have a problem with your "switch"... the way you described it's hookup in the above post "may" be somewhat incorrect, (it's a bit difficult to interpret the wording of your description to an actual hookup scheme) but for now just find the big problem and we can iron out the ground switching stuff later, unless it turns out to BE the problem... Under the conditions you described, it's quite possible that 20 volts can shock you. Getting shocked and needing over 40 volts to do it is only valid if everything's dry. Salty and wet, you can even get it from 12 volts, and believe it or not, people have actually been killed on 12 volts. I remember reading about it in the 60s.... rare but possible. It's not actually anything to do with the voltage- it's getting current to pass over your heart and internally it only takes a few milliamps. Lower your external resistance or impedance enough (with sweat or salty water) and low voltage normally thought of as "safe" can easily force that much current thru your arms... Tom, I really hope you find the problem... spilling beers is unforgivable!!!!  (Message edited by boogiethecat on June 02, 2006) | ||
| Richard Bowyer (Drivingmisslazy)
Rating: N/A |
Great posts guys. I have found this grounding issue the hardest thing to come to grips with and get my arms around so that I understand it. Richard PS and pretty soon some professional or certified commercial electrician or some such will come along and tell you you are full of BS! LOL Richard | ||
| FAST FRED Rating: N/A |
Before working on anything , unplug ALL the items inside the coach. Sometimes somthing plugged in can cause endless false ground readings. FAST FRED | ||
| Tom Dessert (Mci5er)
Rating: N/A |
Ok, here's where I am so far. Since the pigtail adapter(50A to 30A) was ratty I replaced it and started to do some electrical checks starting at the power cable and Iota 50R transfer switch. I unplugged the power cable from the house circuit did a quick resistance reading across the neutral and ground pins on the cable. I got a dead short. I then opened the IOTA switch to where I could see the end of the terminates for the input(house). It visually and electrically appears that the neutral and ground are hard wired together in the transfer switch for the genset and pole 115. One other thing I did was to do a resistance check across the neutral to ground on several 115 wall receptical in the bus. They too indicated a short with no 115 pole connection or genset applied. Going back to John MC9 comments "tie of the neutral and ground is to be made at the source of supply", then would I be correct in saying that in the case of pole power coming in to the transfer switch both shouldn't be bonded? John MC9, my understanding of what you said, was that if the power source is (pole) it is bonded(neutral/ground tied) from the house circuit since this is the source and not at the transfer switch also. Likewise, if the source is the genset, then the genset output should be bonded at the genset not the transfer switch. Is that right, guy's? | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
That's right Tom, and what John said is correct. Ground and neutral should only be tied together at one point, which is at the point where your power comes from. If it's coming from shore, the two should only be tied together at the building's power drop point. If power is coming from your genset, they should be tied together at the genset, and if power is coming from the inverter, they should only be tied together at the inverter. That's why it's messy- you have to switch ground around here and there as you switch power sources, and lots of folks including "licenced electricians" don't grokk that. So it sounds like you have a problem there... although it wouldn't necessarily be an explanation for why you got shocked. The reason for properly bonding ground to neutral at one point only is simply because if they are bonded together at more than one point, what will happen is electrical current that should be confined to the neutral wire will get split and some of it will travel home via the earth ground wire. While this is a no-no, ground is still ground and you shouldn't get shocked if neutral really is neutral and ground really is solidly hooked to earth at the power line drop point on your building, even if they are hooked together inproperly at multiple points... So keep looking... | ||
| John MC9 Rating: N/A |
Yahvoe! The ground and neutral are only tied at the source of power, not at the receptacles, or at the hard-wired ancillaries. If the genset is the power source, then all the wiring connected to it should be ground bonded (neutral/earth) (earth would be the chassis in that case), at the genset. When the wiring in the RV is connected to the power pole, the neutral/earth bond is at the power pole. The transfer switch should be doing the ground swap also, shouldn't it? "One other thing I did was to do a resistance check across the neutral to ground on several 115 wall receptacle in the bus. They too indicated a short with no 115 pole connection or genset applied. " Read Fast Fred's comment above.. If you've unplugged the fridge, and made sure there's no other appliance that's doing the dirty deed (including the inverter), then I guess it'd time to check the outlets? BUT WAIT... you said: "I then opened the IOTA switch to where I could see the end of the terminates for the input(house). It visually and electrically appears that the neutral and ground are hard wired together in the transfer switch for the genset and pole 115. " Isn't that the problem? No sense worrying about anything beyond that point. If it's bonded there, every outlet in the rig will show a dead short between the neutral and ground, representing that bond. This is starting to go well beyond my electrical ability without me actually thinking about what I'm typing... I trust someone else can tell you what that transfer switch should actually be transferring!! Those blasted things always bothered me. I much prefer to swap the plug (source) manually. No mistakes that way! Hey, I can't speak for the others, the guys here are great, and well versed in their fields... But from me? My advice is free as the air, and comes with a degree of pollution. If it sounds right and makes sense, it likely is. If it sounds like BS... well... (Say, you do have a fire extinguisher, right?) I'll see if I can't find a URL for a schematic of transfer switches) | ||
| Tom Dessert (Mci5er)
Rating: N/A |
Additional side note here. I opened the panel at the genset where it connects to the feeder cable back to the transfer switch. Neutral and ground are hard wire together there. I need to get into the electrical compartment and take a really close look at that switch. One more comment just prior to my purchase of the bus back in January 06 the owner at that time upgraded the service power from 30 to 50 amps. This upgrade included replacing the transfer switch. It's possible that it may have not been installed correctly at that time and it's been this way since. The old owner never used the rig after the upgrade was changed. | ||
| herman Rating: N/A |
" I unplugged the power cable from the house circuit did a quick resistance reading across the neutral and ground pins on the cable. I got a dead short. " Ok, that means that the house has a bond between the neutral and ground networks, but it doesn't mean that its ground network is actually grounded to the earth, so check that out: first use several voltage ranges on your meter to see if and how far the ground network is floating above actual earth, then if it doesn't seem mondo (if it were you'd be at risk of frying the remainder of the meter), try the ohmmeter and/or ammeter ranges. The transfer switch should be switching the hot(s) and the neutral. By switching the neutral, the existence of a neutral-ground bond at the inactive source is effectively masked; only the active source's bond is, well, active. So, you need to pull all those bonds in the xfer and move the genset's one to the genset itself, where you should have ground, neutral, genset chassis, and vehicle chassis all bonded together. You should also have the vehicle chassis bonded to the shore cord's ground. Ideally, you have small breaker boxes, one each at shore entrance and genset, containing service entrance breakers and the above bonds. These then feed the xfer switch. Now, how does your inverter fit into the overall topology? Do you have the shore and genset feeding the IOTA xfer, and that going into the inverter, and that then going to your main panel, or does the xfer feed the main panel, with the inverter hanging off of that and feeding a subpanel, or what? Once you describe all this, then we can delve in further. | ||
| niles steckbauer (Niles500)
Rating: N/A |
Please don't confuse the earth ground/bond with the safety/source ground/bond - there is only one earth ground/bond - FWIW | ||
| Tom Dessert (Mci5er)
Rating: N/A |
Here is how this saga ends..... A lot of pearls of wisdom from the contributing members was helpful in my understanding how this all works. Armed with the knowledge, I double checked everything until I was sure the bonding was working correctly. I corrected some bad wiring done by previous owners (ie ganging grounds and neutrals at the inverter input and out vise terminating back at the sub-panel), replaced faulty GFI outlet, replaced 50 -30 amp power pigtail etc. The bottomline here is to be careful about using twist-on wire connectors. Great for houses that don't more or vibrate. Most of my problem was due to poor electrical connections. I prefer to use butt splices (properly sized to wire). I remove the plastic insulation from the splice leaving just the metal tube. Solder (tin) both wires being terminated, slide a piece or two of skrink tubing over one or both leads well past the soldering area, insert the wires into the slice, bending wires as needed to support themselves. Solder everything leaving clean shinny finish. Pull your skrink tubing down and center over the splice, pull out the Zippo heat it and forget it. I spent quite a bit of time fixing my combat squadron's helos using the method above. As a matter of fact 3M Corp. actually made a product called solder-skrink for military apps. It was a sized clear tube that slipped over the tinned or un-tinned wires. It had a small band of solder inside the tube that you could see. Just line it over the wires and hit it with a Zippo. Melted the solder and tubing all at once. Anyway thank you all once again for the support. I started getting worried there for a while about the inverter being bad ($$$$$)specially with a trip to Montana coming up next month. Now I can worry about getting the rest of my nine mile long list done, instead. | ||
| herman Rating: N/A |
Wow, I was taught that a solder joint had, as a prerequisite, a solid mechanical bond. Your description makes no mention of actually putting a crimping tool to the butt splice, so my jaw is just kinda hangin' in the air over here. Did you find the low grade fault(s) that, along with poor continuity in your ground network, led to the witnessed elevation in voltage on said network, or were you able to verify that it was entirely due to neutral current travelling over the ground network due to the multiple bonds? | ||
| Tom Dessert (Mci5er)
Rating: N/A |
Herman, The use of the metal sleeve within the butt connector is used for convenience in my case. You can crimp the connection to stabilize during soldering however I would recommend that you per- tin the wires first to ensure a good heat transfer and proper wicking action. I don't know that I would say it's a prerequisite. Going back to the day of Cannon Connectors(MIL Grade) and solder cups, we build harnesses by soldering the end of the cable directly into the pins of cannon plug thus no mechanical bond other than the tin/lead bonding. I was military trained back in the late 60's and I'm sure technics have changed since then. My gut feeling is the inverter installer didn't following the manufactures installation procedure (ie bonding each neutral and grounds back to the distribution panel). What they actually did was route a single neutral and ground from the panel then ganged everything at the inverter (ac_in, ac_out1 and ac_out2). Electrically this is the same idea, except you just created a single point of failure should either wire come loose. Finally with them trying to jam all those stranded wires into wire nuts, it's hard to say if there was a good electrical connection on each leg. | ||
| Richard Bowyer (Drivingmisslazy)
Rating: N/A |
The mechanical bond in the Cannon connectors is the cable clamp that prevents putting any tension on the soldered leads. I attended the Air Force Electronic school in 1950 and they taught that you always had to have a mechanical connection. The solder was only for electrical connection. I have never heard any change in that philosophy. Richard | ||
| Stan Rating: N/A |
I too went to tech school in 1950 and learned how to wrap wire around tube socket terminals. Somewhere around 1960, printed circuit boards became quite common and no mechanical joint was used. Unless the part is so heavy that it has to be bolted to the board, the robot just sticks the components through the holes and it hits the wave solderer. I have no idea how the boards are made that have tiny unpackaged chips stuck on the solder side. Maybe some of the 'young' tech gurus have the answer for that. | ||
| Tom Dessert (Mci5er)
Rating: N/A |
Guys, It wasn't my intention to start a debate over my training and preferences in making wire connections. Richard, you are correct in that the cable clamps used with cannon connectors provide a strain relief for the soldered wire, as did lacing cord and current day nylon ties. I don't actual see how the clamp provides a mechnical bond for the solder joint, strain relief you bet. I took herman's comments as meaning "crimp the lug, then solder". I don't remember being taught that approach was a "prerequisite" to any and all soldering jobs. I'm ok with the approach I use. I don't care for wire nuts and prefer not to use them. I would recommend to any of our reads to use whatever approach works for them. | ||
| Gary Stadler (Boogiethecat)
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I've been in the electronic manufacturing biz for 35-40 years. Things have changed. Yes in the old days you needed to mechanically secure wires to the terminal and solder was only considered as electrical. But nowadays solder is both mechanical and electrical. Most military connectors that aren't crimped use "cup" solder pins... basically a little tube that you stick the wire in and fill with solder. That form, which is quite a bit like the one described by Tom, is quite decent both mecahanically and electrically. My personal experience is that solder is a very good mechanical joiner regardless of what the industry says. Much more important than fastening the wire mechanically first, is to do a decent joint that is not "cold" Ie don't wiggle the joint until the solder has solidified, or the solder will be visually ugly and internally poor both mechanically and electrically. If it's not a pretty, shiny joint, re flux it, do it over and get it right. Woah...what happened to getting shocked? The thread took a wrong turn... | ||
| Tom Dessert (Mci5er)
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Gary, The problem went away as a result of changing the wiring configuration to the inverter. In the original post I mentioned that there was a hum from the inverter and the voltage to earth ground varied with the audio intensity of the hum. Thus far it hasn't returned and I'm checking it daily under any condition I can think of. I hate to admit it given the circumstances, but I've worked in electronics for 32 years, 10 military and 22 civil service as a GS-12 electronics supervisor. I was a technical instructor/inspector for various computer systems used onboard the Trident Submarines as well as a DOD certified micro/miniature soldering instruction. I have years of experience with AC/DC circuits but knew nothing first hand on how these buses are setup electrically. so with all this experience, I have no problem admitting I don't know it all. I'm glad I got a place to asked for help from the people that know. My way of thinking is "everyday is a learning day". | ||
| Gary Stadler (Boogiethecat)
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Hey Glad it worked out~!~ And don't feel bad- I make electrical mistakes all the time and I've been doing serious electrical/electronic design for many years. If I don't look into the mirror at least once a day and say "duh" to myself, I think something's wrong!!! Happy crawling under your bus... sans the tickles |