Ground showing voltage?

Re: Ground showing voltage?

Well, then I have a misunderstanding because I thought from your first post that this is for an off-grid cabin with standalone power. Now you have shore power to the place? So you are connecting to the utility? And the inverter is bonded neutral? This is a new can of worms.

Firstly, what is the brand and model of this inverter? It needs to be verified that it DOES have a bonded neutral. Can you please try a test for me? Shut the thing down and disconnect the battery power to it. With an ohm meter check for continuity between the neutral blade (the wider of the two slots in a plug) and the inverter frame ground stud.

Edit:
I may have misread your post - I see you are running inverter output to the shore power input on the transfer switch.

Could you check BOTH your generator and inverter for bonded neutrals for me? Both are checked in the same way, as noted above.
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Chris

Re: Ground showing voltage?

It took me a little bit to find the specs on that inverter. It does indeed have an internal neutral ground bond. Which means, as they told you, neutral and ground remains separate in the service panel. And you wire it just like a house - GFCI and single pole breakers and switches all work as normal. However, because of the MSW, you may experience some buzz in GFCI transformers.

However, the inverter becomes the utility transformer or service entrance (in NEC parlance) because it has the neutral ground bond. You can not have another neutral ground bond in the system anywhere. So your generator is fine, you put neutral on the neutral bus in the box, and hot to the hot buses. You must install a separate ground bar for the grounds in that box.

In your transfer switch neutral is pass-thru from the generator to the system neutral and MUST be connected to the inverter neutral in order for the bonding to remain in effect. So you only switch the hot wire in the transfer switch.

For grounding, you drive a ground rod for the inverter and the inverter's grounding lug is connected to it. This is your earth ground. Battery bank ground is also connected to that same ground rod with a separate wire and clamp on the ground rod. Do not drive a ground rod for the generator. The generator frame is connected to system ground thru the grounding pin when it's connected to the system.

You should be fully wired to code with that setup, as far as neutrals and grounding goes. The reason you were seeing a small amount of voltage is due to leakage and the fact that the unit was not grounded properly. There should be no potential (voltage difference) between grounds. Connecting BOTH DC and AC grounds to the common grounding point insures that potential does not exist between them.
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Chris

Re: Ground showing voltage?

All those grounds go to the same ground rod, regardless of how they get there. Typically there will be a grounding bar in your service panel where the ground connections from circuits and components will be made. Once the inverter frame or ground stud is connected to the ground rod, there are three wires that come from the inverter to feed the distribution panel (hot, neutral and ground). That ground from the inverter provides the ground path to the ground rod for that panel. And so on.

There will typically only be two large bare copper wires going to the ground rod for an off-grid power system - one from the inverter or service entrance panel (which ever has the neutral/ground bond made in it), and the other from the battery bank negative bus bar.

Having your test setup connected to your home ground rod is no issue at all.

It's really nice that you got a DECENT MSW inverter. Looking over the specs on that unit, it looks fairly robust.
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Chris

Re: Ground showing voltage?

I found several references to them being used in ambulances. Usually stuff that is used in ambulances is not junk.
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Chris