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Neutral bonded to ground or no?


Jimalberta

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Hi guys...this is for you Electrical guys....I am just finishing up installing a new charger/ inverter in my MH and the sub panel has a bonded neutral to ground screw....do I remove this screw?

 

I tried plugging the MH into my house and the GFCI plugged tripped where it didnt before this new system.

Am I correct in assuming the culprit is this bonding screw?

 

Thanks

Jim

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Your shore power is bonded neutral to ground. That's why the inverter has a relay that unbonds it when shore power is connected. If neutral is bonded to ground in your rig (downstream of the shore power box's GFCI) with shore power connected, it will trip your GFCI.

 

So, yes. Ditch the bonding screw.

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I think you and Yarome have the problem fixed........... Indeed, the RV panel is considered as a SUB PANEL which has its Neutral Buss and Equipment Ground Buss separate and electrically insulated and isolated from each other. There is to be ONLY ONE Neutral to Ground Bond (lots of reasons not covered here) and that takes place at the RV parks distribution panel or your homes Main Panel etc.

 

NOTE HOWEVER the RV panel needs it metal case/frame bonded to the Equipment Ground Buss (that's NOT the Neutral Buss) just as any other non current carrying metal junction boxes need bonded. Of course, the RV's frame needs to be bonded to the Ground Buss also. Bonding the metal case/frame to the Equipment Ground Buss (perhaps by a screw in the Ground buss into the metal case) IS NOT the same as bonding Neutral to Ground mind you.

 

If you create a second additional downstream NG bond, the Bare/Green Equipment Grounding Conductor is in parallel with the Neutral conductor and carrying current so all flowing out the Hot is NOT all returned by the Neutral WHICH TRIPS A GFCI if as little as around 5 milliamps difference.........It takes something like 30 to 50 milliamps to fibrillate the old ticker OUCH

 

John T

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Most of those installation manuals are pretty confusing in that regard. At least the ones I've run across. They are generally pretty clear about the need for an NG bond, but don't specify 'where' the bonding should be taking place in which type of application. For RV's it's bonded at the shore power source. Then they have a grounding terminal, which can make it that much more confusing for most DIY'rs. Keeping in the back of our minds that inverter/chargers are not RV specific appliances.. that bonding terminal has it's place in some applications.. just not ours.

 

Of course.. if they tried to cover every application installation, the manuals would end up costing more than the equipment. ;)

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Yarome, you say "Most of those installation manuals are pretty confusing in that regard"

 

HOW TRUE I've seen them simply say BOND IN ACCORDANCE WITH NEC Now that really tells the typical RV owner a lot now don't it lol

As an engineer and attorney, I've found the NEC harder to follow and understand then many legal statutes. It cant have one complete sentence without referring back to 3 or 4 or more other sections, it can drive a body to drink. Of course, lawyers put that in the instructions to cover their %$#@@

 

Without a Neutral to Equipment Ground Buss the safety features and design and purpose of it in the first place can never be realized, and if there's more then one, that creates a whole other bunch of safety issues.

 

As I've stated before, the correct Neutral Ground Bond where transfer switches or methods are different can depend on how many poles the transfer switch or device or method switches,,,,,,,,,,,,whether or not the energy source is a Separately Derived Source,,,,,,,,,,,,how the energy source is wired and configured.

 

Its all more then a lay person can understand and couple that with the fact I don't usually have the Inverters output wiring diagram and know if its a isolation transformer or if it has a true Neutral or if it has any Neutral Ground Bond, its just hard for me to tell people how to wire their devices SO I SAY DO AS MANUFACTURER SUGGESTS (that's the lawyer side of my brain working) There are situations where you DO NOT want a bond at a Generator and there are situations where you do, I understand all that but cant explain it here to a lay person in a few paragraphs

 

John T

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...There are situations where you DO NOT want a bond at a Generator and there are situations where you do, I understand all that but cant explain it here to a lay person in a few paragraphs

 

John T

 

Rather than trying to explain the when to & when not bond a generator, this PDF does a pretty good job, and uses plain english to explain both NEC & OSHA requirements. Well worth reading.

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Well this morning I intend to remove the bonding screw from the sub panel and retest everything. I dont know if the new transfer switch bonds the neutral to ground or not but I am going to assume no for now. All of the new components, the transfer switch, the Magnum inverter charger and the sub panel are grounded to the chassis. Just need to make sure that the neutral is floating.

Interestingly I phoned American Coach several times on this project just to clarify things and this was one of my questions and I was specifically told by a tech lady there to make sure that the neutral was grounded. Nice help eh?

Thanks everyone for their input.

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Vermilye,

 

"Rather than trying to explain the when to & when not bond a generator, this PDF does a pretty good job, and uses plain english to explain both NEC & OSHA requirements. Well worth reading."

 

That's a good article, I had it in my library, has references to NEC and it talks about the Separately Derived Systems I mentioned before.

 

In a non perfect not exact very over basic nutshell, if your transfer switch DOES NOT switch the Neutrals (less poles cheaper switch), then the genset MUST NOT be configured as a Separately Derived Source and the gensets Neutral is floated (you have to sever any Neutral to case bond). If your transfer switch does switch the Neutral (or say you plug RV power cord into genset, that switches the Neutral) then the genset must be configured as a Separately Derived Source and have the Neutral to Equipment Ground Bond. Whether or not connection to another Grounding Electrode is required is another issue.

 

Hope this helps but Id guess it confuses lay persons as this is NOT real simple..........

 

 

JImalberta,

 

"I dont know if the new transfer switch bonds the neutral to ground or not but I am going to assume no for now."

 

Id agree, Probably NOT, the Neutral to Ground Bond would take place at a Generator (if a Separately Derived Source) or at the RV Parks (or your home) Main Service Entrance Panelboard. WHATS REALLY IMPORTANT IS HOW MANY POLES IT HAS AND IF IT SWITCHES THE NEUTRAL OR NOT!!!!!!!!!!!!!!!!!!!!!!

 

"Just need to make sure that the neutral is floating."

 

That's correct if the energy source is NOT a separately derived source and you do NOT switch the Neutral

PS HOWEVER If by "floating" you mean that in the RV Panel Neutral Buss is NOT bonded to Ground Buss THATS CORRECT

 

"Interestingly I phoned American Coach several times on this project just to clarify things and this was one of my questions and I was specifically told by a tech lady there to make sure that the neutral was grounded."

 

That's the answer Id expect to be safe and legal and avoid lawsuits. HOWEVER earth grounding of the Neutral (done at main panel or service drop or meter base and out on utility pole transformer) IS NOT THE SAME AS NEUTRAL TO EQUIPMENT GROUND BOND

 

Earth grounding of the Neutral (for grid stabilization and surge and lightning protection) is NOT the same as Neutral/Equipment Ground bonding for shock protection !!!!!!!!!!!!!!!!!!!!!!!

 

 

Sorry, I cant put in a few sentences what takes books and study to fully comprehend, but hey I try lol

 

 

John T

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Ok ..removed the bonding screw on my sub panel and the coach can now be plugged into my 20 amp gfci outlet on the house and it works.

UNTIL I started the gen. Same problem ...the gen kicks out the gfi outlet on the house. So I unplugged the shore power, turned off the gen and started checking the connections in the transfer switch.....I have a reading from the gen neutral lug to ground......great. Tried phoning Parallax but they are gone for the weekend so I will have to wait till monday to see if I can get an answer on how to unground that gen neutral...I am assuming thats what I want to do. Its a Parallax ATS 503 50 amp transfer switch. The manual that came with it is poor to say the least.

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Jim, here's my response to your updated statements above:

 

 

1) "Same problem ...the gen kicks out the gfi outlet on the house"

 

If you're plugged into the house GFCI receptacle and the Generator is in the circuit somehow???? and it has its Neutral bonded to its case/frame (a second downstream Neutral/Ground Bond is a no no) which is bonded to the RV frame which is also bonded to the RV's Sub Panels Equipment Ground Buss, that may cause a problem in a GFCI sensing circuit tripping it. If I were going to run the generator I would un plug from the house receptacle.

 

 

2) ". So I unplugged the shore power, turned off the gen and started checking the connections in the transfer switch.....I have a reading from the gen neutral lug to ground......great."

 

If the generator is an onboard unit and is like mine and many I've seen, its a SEPARATELY DERIVED SOURCE and has no connection to other electrical service,,,,,,,,,,Has its Neutral bonded to its case/frame,,,,,,,,,,,,,The RV sub panel has the RV frame (to which the generator frame is also bonded) bonded to its Equipment Ground Buss,,,,,,,,,,SO I WOULD EXPECT THE GENERATOR NEUTRAL TO HAVE A LOW RESISTANCE TO THE RV FRAME AND THE GENERATOR FRAME AND THE TRANSFER SWITCHES METAL CASE.

 

NOTE just because we all told you inside the RV Panel Neutral is isolated from Ground, THAT DOES NOT MEAN THERES NO NEUTRAL GROUND BOND AT A GENERATOR OR INVERTER (if configured as a Separately Derived System) !!!!!!!!!!!!!!!!!!!!!!!!!

 

I may have mis understood your post above, but if you unplug from the house when the RV generator is operating all may be fine??????????????

 

 

SUMMARY RV sub panel has Neutral and Ground separate and isolated and insulated,,,,,,,,,,,RV frame is bonded to sub panels Ground Buss,,,,,,,,,,,,,,,,,,,,If genny is a Separately derived Source with no connection to other electric service and the transfer switch switches all hots PLUS Neutral, the Genny would have its Neutral bonded to its case/frame which is also bonded to RV frame and sub panels ground buss.

 

Im not a good teacher but that's all I know to say and again I cant cover in a paragraph what may take a book to understand, sorry.

 

John T

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Thanks for that John. You make a good point. When I checked the gen neutral lug to ground the neutral wire from the gen was hooked up. You are saying that this might be grounded at the gen? The gen does run and operate seemingly normally if I unplug from shore power and I never really have run the gen when connected to shore power...no need to.

 

Possibly all is ok then....but for my own peace of mind I want to know for sure. I probably should disconnect the gen wires from the transfer switch and then see if the neutral lug is still grounded....baby steps.

 

However I thought the purpose of the transfer switch was to be able to switch power sources seamlessly?

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The rules for Neutral to Ground binding are that the bonding should occur as close to the source as possible.

 

A generator or an inverter are sources and the Neutral to Ground bonding should occur in the device. The Power Company for the park is a source. The usual closest point to the Power Company source is the main panel for the park.

 

The change of location of Neutral to Ground bonding when switching from park power to either generator or inverter, a transfer switch is mandatory. Most inverter/chargers have built-in transfer switches. Generator do not have transfer switches and therefore require an external transfer switch. The key element to the transfer switch is that the Neutral is switched, so when the generator is not switched on, the generator's Neutral to Ground bonding is disconnected from the RV.

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Jim, this seems its getting more complicated then it needs to be. NOT being there I cant say for sure, but FWIW here's my best educated guess of how it may be wired and I know for sure its how the many many motorhomes with on board gensets I have owned have been wired: This method (cant say you have it or not???) satisfies the NEC and the onboard genset with a Neutral/Ground Bond is considered as a "Separately Derived Source" and the Transfer switch MUST switch BOTH Hot and Neutral. If you have a floating Neutral Genset, I would have to revise that which is below !!!!!!!!!!!!!!!!!!!!!!!!! NOTE Im talking 120 volt 30 amp here NOT 120/240 50 amp like a bigger Class A has, if that's the case I have to revive that below................

 

 

1) INSIDE the Genset, the outgoing Neutral is somewhere somehow bonded to the gensets case/frame, and that case frame is attached to the RV frame which is bonded to the RV Panelboards Equipment Ground Buss. UNLESS its a genset with a Floating Neutral as some come from the factory.

 

2) If everything is disconnected from the gensets output wiring that leads elsewhere. For example if its wired to a female 30 amp receptacle, insure nothing like the RV power cord is plugged into it, if its wired direct to a transfer switch, unhook all wires (I assume 3, Hot Neutral and Ground) that go from the genset into the switch.

 

3) See if there's continuity (very low ohms) from the gensets output Neutral to gensets Ground (or its case/frame)???? If its connected it has a Neutral/Ground Bond, if its NOT connected it has a floating Neutral.

 

4) The transfer switches metal case/frame needs a bond to the Panels Equipment Ground Buss which (if wired as I suspect with a genset Neutra/Ground Bond) would also have continuity to the gensets ground and the RV frame etc.

 

5) If wired as I suspect (remember Im not there so I cant guarantee!!!!!) the Transfer switch has two switching poles, one for Hot other for Neutral from BOTH sources, utility RV pedestal or home power receptacle AND Genset. If the transfer switch is set to Utility/Home, power comes from utility and is switched to RV Panelboard. If set to aux or genset power, gensets power Hot and Neutral goes to RV panelboard.

 

If you have an inverter, I cant say for sure without diagram, it may have a relay that connects its Neutral to case/frame ground when its powered up and supplying 120 VAC so otherwise its NOT.

 

Again remember, that even though inside the RV panel Neutral and Ground must be isolated, that does NOT mean theres no Neutral/Ground bond in a genset or an inverter. Also the gensets case/frame plus the RV frame plus a metal transfer switch case/frame will have a bond to the RV panels Equipment Ground Buss. If your genset has a non floating Neutral/Ground Bond to the gensets case/frame, then the gensets Neutral will also show continuity to the RV frame and equipment Ground Buss etc.

 

Best I can do, Im wearing down and runnin outa smarts lol but glad to help if I did???????????

 

John T

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Yo Mark and Dale, " The key element to the transfer switch is that the Neutral is switched, so when the generator is not switched on, the generator's Neutral to Ground bonding is disconnected from the RV."

 

EXACTLY there is to be only one Neutral/Ground Bond preferably at the source and NO MORE BONDS DOWNSTREAM.

 

Contrary, in "some" home emergency generator set ups the Neutral may not be switched in which case the gensets Neutral is floated while its case/frame is bonded to the utility equipment Ground Buss and the genset is NOT a "Separately Derived Source"

 

John T

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Stop running the generator while plug into a functional AC outlet.

 

Yes ...the simplest solution and normally how we function.

 

I only use the built in 7500 W onan quiet diesel when boondocking and need to use the microwave or sometimes the coffee maker. The Magnum ( MS 2012) 2000 W PSW inverter is used for watching TV and such other light loads.

I carry a Honda 2000i that we use for topping up batteries and such on cloudy days....might not need it much anymore as I recently installed 310 watts of solar panels going through a charge controller to 4 six volt batteries which I have also replaced within the last six months. There..... now you guys know as much about this coach as I do.

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