| Author |
Message |
Mike Tornesello (206.170.33.68)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, May 28, 2002 - 9:52 pm: | |
I figured I was being clever. Correct me please if I'm wrong. Neutral is connected to ground(chassis) when not connected to shore power. I'm using the Trace Manual for diagrams which show a single pole double throw relay switching the main panel neutral to chassis/ground in one instance, to shore neutral in the other instance. I say why not have the shore neutral and the panel neutral connected all of the time since it is going nowhere if you are not hooked up. Then install a relay that connects the panel neutral to the chassis/ground for when you are not on shore power. One more step to the thought is that it would be better to have the relay be normally closed connecting panel neutral to chassis/ground and when you plug into shore power, 110 volt from your shore cord opens the contacts on the relay to disconnect neutral from chassis/ground making the bond(neutral to ground) only happen at the RV park power pole. You would think I could find a SPST Normally Closed, 110v coil relay with contactors rated at 50A but I can't. I've tried MSC, Grainger, all of the links I can find with extensive internet search. Please help guys. Thanks |
Richard Bowyer (Drivingmisslazy) (66.190.119.82)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, May 28, 2002 - 10:25 pm: | |
Mike, suggest you use dpdt relays. They are available at 30 amps per pole. Just parallel the two sets of poles. These should be readily available from any electronic supply parts house. As I recall, I used to pay about $15.00 for them.
I really can not comment on your scheme as I do not have time right now to draw it out and understand, but I suspect that you will end up with either a neutral improperly grounded, or circulating ground currents or something not wired according to NEC.
Richard |
Mike T (206.170.3.47)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, May 28, 2002 - 10:44 pm: | |
wow that was fast. But now I'm worried. I'm taking the power for the relay right off the shore cord in it's junction box were it splits to two inverters and mounting the relay right in that box. I doubt NEC covers my scenario but I'm wide open to comments. Thanks Richard, I'll do some more research (and muttering to myself as usual). |
Jim Stacy (12.87.111.128)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, May 28, 2002 - 10:51 pm: | |
Mike,
Your Trace inverter probably has a relay to provide a neutral/ground connection when it is working as the source. Your gen set should have a neutral/ground connection wired at the gen set for when it is acting as a source. The gen set should be isolated by a transfer switch designed for the purpose or a manual plug with two receptacles to control it manually. Be certain your ground (green wire) does NOT go through a set of contacts to provide chassis ground. This must be hard wired per code.
HTH
Jim Stacy |
Eric K (12.228.168.96)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, May 28, 2002 - 11:00 pm: | |
If you bond the neutral and ground together in the bus, any GFI outlet you plug the bus into should trip. This happens when the hot and the return currents don't match.
Makes it hard to stay "powered up" in some of those great, "out of the way" camp sites. |
Mike Tornesello (206.170.3.2)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, May 28, 2002 - 11:04 pm: | |
Thanks Jim,
Trace specifically states that the relay is to be part of the ac installation and the bond switching is not provided because the inverter is considered a serviceable item. If it is removed, you would lose this important safety feature. The inverters are, however, the transfer switch. They detect power from whichever source is present and, in the case of the coach conversion model, the generator is actually the default in that it looks there first.
On my ground, I am attached to chassis with a hard connection always. The only part I'm trying to put through the contacts is the green ground to neutral/white/from the panel for the on-the-road and boondocking scenarios.
I do appreciate the feedback. You never know when you're missing a twist in the plan. |
jmaxwell (66.42.92.15)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, May 29, 2002 - 12:43 am: | |
I may be lost here, but I think Erik is onto what u propose as a bad idea. Why the relay? Everything on the bus is grounded to chassis, including the genset and inverter, isolated from neutral. Power cord ground is also tied to chassis ground. So, why do u insist on tying ground and neutral together. My Trace does not specify an external relay, but mine may be a different model. Bottom line, u never switch ground |
Jim Ashworth (Jimnh) (172.134.168.208)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, May 29, 2002 - 12:27 pm: | |
If it is a Trace sinewave inverter, the installer needs to bond ground and neutral when the inverter is the source, since the inverter has no capability to do so. That being said, there is no perfect way to do it and Mike has chosen the lesser of two evils. Using a normally closed relay, neutral and ground are bonded when off shore or genset power. When either of these sources are active, the relay opens and bonding occurs at the campground supply or genset. What if it fails? Yes, code will be violated at that point since it shouldn't be bonded when shore power is available. On the other hand, what if a normally open relay is used and closed by the inverter power? If the relay fails, there will be no bonding anywhere. Since most campgrounds are properly wired, the lesser of these evils is to ground again at the bus panel rather than to risk no ground at all. When I talked to Trace about this, they said a 5 amp relay would be all that was needed. I went with a 2 pole 30 amp like Richard suggested.
Jim |
Mike T (206.170.3.176)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, May 29, 2002 - 6:01 pm: | |
Jim, Thanks very much for the affirmation. You understand exactly what I was after. AND Thanks to all once again. Great board. Another challenge overcome!
Ian, It sounds like you and I may have bought our rigs from the same guy if Vulcan did the conversion. Mississippi? |
David Anderson (168.215.176.128)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, May 29, 2002 - 10:55 pm: | |
If the relay is closed and the circuit is made (neutral to ground) won't the GFI trip every time you plug into the pole at the campground?
I made a portable 50amp female plug in a j-box with a #6 wire jumper from neutral to ground inside the box. I plug it into my shore cord when on inverter power. I leave it plugged in when on Genset power because the Auto transfer switch transfers all hots and neutral to the genset, thereby eliminating the entire length of the shore cord and its circuit disconnect from the wiring scheme.
I don't know if it meets code, but I'm unbonded when on shore power, bonded on inverter power, bonded at the genset on genset power.
Paid about $12 for the plug |
Mike T (206.170.3.60)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 30, 2002 - 8:06 pm: | |
David, I'm not sure about that scenario. Again, I am modifying a scenario that I read in the Trace Inverter manual. The problem is that although they show a relay making and breaking the bond, they don't show what power operates the relay. Your point is well taken. That was Eric K's point earlier in the string and I'm still not clear until I do some experimenting. In a house panel with neutral and ground bonded at the main but not sub panels, this all seems to work but I'm not sure if that logic carries through. |
David Anderson (168.215.176.149)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, May 31, 2002 - 12:33 am: | |
Mike, I spent hours drawing a relay setup from the example Dick Wright sent me from a Trace manual. It used a couple of Xantrax 30 amp double pole, double throw contactor/relays to bond neutral and ground while inverting. It would work, but I just mentally put myself through all the "what if" situations of relay failures, etc. and I didn't feel totally comfortable with the setup. The plug was so much easier and foolproof unless I forget to plug it on the cord.
There seems to be no clear way to do this because it is discussed over and over again. I've come to the conclusion if you touch a hot wire to the bus frame or to your neutral wire and the breaker pops, you're safe. Maybe that is too elementary, but I want the ciruit to break anytime 120 volt ac is not where it is supposed to be. |
Mike T (206.170.3.97)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, May 31, 2002 - 7:23 pm: | |
David, I'm hearing you loud and clear. It sounds like I'm doing exactly what you were doing (at least mentally). I think you're right about everything that you said, especially how much this is debated. I'm not quite ready to "let it go" but safety first rings loud and clear. I'm thinking pilot light on the relay or manual switch for the relay. If I'm not careful this little part of my big project will just take up too much attention. Thanks for your idea. Mike |
David Anderson (168.215.176.121)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, May 31, 2002 - 10:06 pm: | |
I drew in the pilot light, too when I was drawing a schematic. I still didn't like the wiring.
David |