Unique Victron Ground/Bonding Question

[Watts Happening]

I've got a bit of a head scratcher here, at least I think. I've got a trailer that will have (2) Victron Multiplus-II 48v/3000 inverters, they'll be in split phase feeding a breaker panel inside the trailer. Being that this is the "main panel" of the trailer, I would expect to be installing a ground neutral bond screw in the panel as you'd see in a typical residential main panel. I'll obviously ground the breaker panel and inverter cases to the frame of the trailer. If any of this seems incorrect, please let me know.

The part that has me really wondering is; I'll be setting the trailer up to have an exterior 240v plug, this will be used if we lose power in our home, in this context consider the trailer, it's batteries and inverters as a "generator" to the house. If running a generator cord from the side of the trailer, to a generator inlet on the house, how would this affect my previously mentioned grounding/bonding situation? At that point I suppose the house becomes a sub panel, with the trailer being the main panel. I can't quite decide how this should be handled wiring wise?

A generator providing power to a house generally doesn't have any type of grounding, at least most scenarios I see. I would think the generator is getting its ground from the house's ground via the extension cord. I imagine that's what would happen to my inverters as well, but, I don't know how that would affect the panel inside the trailer.

Thoughts?

 

[FilterGuy]

I've got a bit of a head scratcher here, at least I think. I've got a trailer that will have (2) Victron Multiplus-II 48v/3000 inverters, they'll be in split phase feeding a breaker panel inside the trailer. Being that this is the "main panel" of the trailer, I would expect to be installing a ground neutral bond screw in the panel as you'd see in a typical residential main panel. I'll obviously ground the breaker panel and inverter cases to the frame of the trailer. If any of this seems incorrect, please let me know.

NO! Do not put an NG bond in your trailer distribution panel. The inverters do the bonding!




Note: When the two multiplus inverters get set up properly for split phase one of the two of them will disable the internal NG bond. (Only one of the two will do the bonding.)

The part that has me really wondering is; I'll be setting the trailer up to have an exterior 240v plug, this will be used if we lose power in our home, in this context consider the trailer, it's batteries and inverters as a "generator" to the house. If running a generator cord from the side of the trailer, to a generator inlet on the house, how would this affect my previously mentioned grounding/bonding situation? At that point I suppose the house becomes a sub panel, with the trailer being the main panel. I can't quite decide how this should be handled wiring wise?

A generator providing power to a house generally doesn't have any type of grounding, at least most scenarios I see. I would think the generator is getting its ground from the house's ground via the extension cord. I imagine that's what would happen to my inverters as well, but, I don't know how that would affect the panel inside the trailer.

Interesting problem set.

You are correct that in almost all cases where there is an emergency generator plugged into a house, the generator does not have a bond. Therefore, plugging the trailer into the house as an 'emergency generator' becomes a problem.

There are a couple of approaches.

The best approach is to have a critical load panel and a neutral switching transfer switch:

 

[FilterGuy]

The other approach is to somehow disable the bonding in the trailer when it is used as a generator. (I think you can program the Multiplus' to never bond). The problem with this is that 1) It is a PITA and 2, If you forget to put it back when you are out and about with the trailer, it is a safety issue.

 

[Watts Happening]

The other approach is to somehow disable the bonding in the trailer when it is used as a generator. (I think you can program the Multiplus' to never bond). The problem with this is that 1) It is a PITA and 2, If you forget to put it back when you are out and about with the trailer, it is a safety issue.

Excellent points, I sincerely appreciate your detailed response. I feel stupid for forgetting the fact that the switching happens in the main unit, something I’m familiar with from my prior 43’ fifth wheel with tons of solar/lithium.

Great idea on the neutral switching critical loads panel too, a quick google from my phone on the couch seems like I can accomplish this via a single panel: https://www.eaton.com/content/dam/e...ng-manual-transfer-switch-manual-ib708704.pdf

 

[FilterGuy]

Excellent points, I sincerely appreciate your detailed response. I feel stupid for forgetting the fact that the switching happens in the main unit, something I’m familiar with from my prior 43’ fifth wheel with tons of solar/lithium.

Great idea on the neutral switching critical loads panel too, a quick google from my phone on the couch seems like I can accomplish this via a single panel: https://www.eaton.com/content/dam/e...ng-manual-transfer-switch-manual-ib708704.pdf

yup! That would work.

 

[FilterGuy]

Excellent points, I sincerely appreciate your detailed response. I feel stupid for forgetting the fact that the switching happens in the main unit, something I’m familiar with from my prior 43’ fifth wheel with tons of solar/lithium.

Great idea on the neutral switching critical loads panel too, a quick google from my phone on the couch seems like I can accomplish this via a single panel: https://www.eaton.com/content/dam/e...ng-manual-transfer-switch-manual-ib708704.pdf

BTW: I had not seen that panel before. The fact that it can switch neutral is pretty slick. Thanks for sharing.

 

[Watts Happening]

BTW: I had not seen that panel before. The fact that it can switch neutral is pretty slick. Thanks for sharing.

Back to the drawing board, I cannot find any of them, nor the Reliance X-Series panels (which seemingly do the same thing) in stock anywhere. I will specifically need an outdoor panel as well, which complicates it even further.

Any ideas on components that would work?

I'm surprised this is hard to find, there have to be a TON of people running generators with internal GFCI/neutral bonding all across America with the wrong transfer switch, right? What is my real "risk" here, just so I can think it all through. Thanks!

 

[FilterGuy]

There are not many neutral switch 240V transfer Switch plus Pannel products. You might have to have a transfer switch separate from the panel.

 

[Watts Happening]

There are not many neutral switch 240V transfer Switch plus Pannel products. You might have to have a transfer switch separate from the panel.

Any products in mind for the transfer switch? Seems most don't do the neutral either :/

 

[Watts Happening]

Ok, I can't find anything that seems like a truly viable product, I've done hours of searching and it seems defeating. How about this (questionable) idea.

Step 1: Disable all neutral ground bonding in software.
Step 2: Wire up a "light switch" (or whatever similar device) with a wire connected one side to ground bar, other side to neutral bar.
Step 3: Label said switch with the off position being "generator mode", on position being "normal mode"

That would make it as easy as flipping a light switch type device to enable/disable the ground neutral bond. Sure, you have to remember it, but with as rare as I'd be using it, it seems feasible and allows me to use off the shelf critical load panels.

The only other safety thing I can imagine would be when the switch is set to off, the trailer now has a floating neutral, but I'm not AC power smart enough to know if that matters in a realistic sense.

 

[FilterGuy]

The only other safety thing I can imagine would be when the switch is set to off, the trailer now has a floating neutral, but I'm not AC power smart enough to know if that matters in a realistic sense.

Floating systems can be made safely, but they are also known to suffer from static damage much easier. Even in a trailer, having the circuit anchored to the chassis prevents voltage differential between the circuit and the rest of the trailer.

 

[Watts Happening]

Floating systems can be made safely, but they are also known to suffer from static damage much easier. Even in a trailer, having the circuit anchored to the chassis prevents voltage differential between the circuit and the rest of the trailer.

All of that said, what would you do?

 

[FilterGuy]

All of that said, what would you do?

Good question.

I did not look very hard for a transfer switch, but the ones I saw were crazy expensive..... I would look hard for one but if I could not find one I would look at doing something like what you describe.

Will you ever be plugging the trailer into shore power?

 

[Watts Happening]

Good question.

I did not look very hard for a transfer switch, but the ones I saw were crazy expensive..... I would look hard for one but if I could not find one I would look at doing something like what you describe.

Will you ever be plugging the trailer into shore power?

The trailer is indeed set up to be plugged into shore power. Albeit rare, it very likely will happen.
Thus far, the closest thing to "safe and easy" seems to be the light switch idea. I don't suppose this would require a massive conductor as it would only serve to trigger a breaker being tripped, am I thinking about that correctly?

 

[FilterGuy]

I don't suppose this would require a massive conductor as it would only serve to trigger a breaker being tripped, am I thinking about that correctly?

It does not need to be massive, but it should be the same size as the power conductor to the house.

Keep in mind that if the switch is left on when you are on shore power there will be two NG bonds.... and that is not good either.

 

[Watts Happening]

It does not need to be massive, but it should be the same size as the power conductor to the house.

Keep in mind that if the switch is left on when you are on shore power there will be two NG bonds.... and that is not good either.

Thus my switch would need to be labeled "off grid" in the on position and "grid connected" in the off position.

More or less grid connected meaning anytime a cord of any kind is connected to the grid, whether to or from said grid.

Seemingly smart?

 

[FilterGuy]

Thus my switch would need to be labeled "off grid" in the on position and "grid connected" in the off position.

More or less grid connected meaning anytime a cord of any kind is connected to the grid, whether to or from said grid.

Seemingly smart?

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