Continuity on Inverter

[dsaint1884]

Without any cables on the inverter at all I used a multi-meter to test continuity at different points on the inverter. The neutral and ground for the AC side are bonded, so I do get continuity there which makes sense to me.

However, on the DC side if I touch the negative DC cable connection terminal as well as the small grounding lug, I get continuity there as well. If these are somehow connected then why would I even need the grounding lug or a grounding wire? It seems like the grounding lug (as well as the metal parts of the frame for the inverter) are already bonded tot he negative DC batter output terminal somewhere in the system. So I get continuity between all of the following: the negative battery terminal, the metal inverter frame, the grounding lug, the AC ground (and the AC neutral because it's bonded to ground).

Perhaps the best way to ask the question is, should I have continuity between the grounding lug and the negative battery terminal?

 

[FilterGuy]

Perhaps the best way to ask the question is, should I have continuity between the grounding lug and the negative battery terminal?

That is a little surprising. What inverter do you have?

 

[dsaint1884]

That is a little surprising. What inverter do you have?

I thought so as well. Renogy 1000w Inverter.

1000W 12V Pure Sine Wave Inverter

Help power your cabin with Renogy's 1000W 12V Pure Sine Wave Inverter. This inverter helps you run electricity through your off-grid system. Free shipping

www.renogy.com

 

[timselectric]

It's possible that you are reading through a ground detection circuit.

 

[dsaint1884]

It's possible that you are reading through a ground detection circuit.

Interesting. I'm not sure what to take away from that or if I should still be worried.

I get continuity from AC neutral (which is internally bonded to ground) to the Negative DC terminal. I get continuity from the Grounding lug to the Negative DC terminal as well.

It seems like everything is connected, but if that's the case why even have the grounding lug or tell me to use it in the manual. It's all seemingly connected to the DC negative terminal anyway. Maybe they tell me to ground the grounding lug to cover their basis in the event that my negative DC connection doesn't lead to a chassis ground (it does, but right now the inverter isn't connected to anything at all yet).

 

[dsaint1884]

I just got off the phone with Renogy. They said the connections and continuity than I'm seeing are normal. That it's all connected somewhere in the device. Does anyone else see this with other brands? They also said that because of this continuity, if my negative DC terminal is running to a bus bar and the bus bar is running to negative chassis, then I do not need to use the grounding lug to chassis ground as the device would be grounded through the negative battery terminal given the internal connection. Wild.

 

[FilterGuy]

Does anyone else see this with other brands?

Connecting DC Negative to the chassis is unusual. I have not seen this on any other inverter. There is nothing 'wrong' with this I guess but it does mean the Battery circuit will be a grounded circuit whether you want this or not.

They also said that because of this continuity, if my negative DC terminal is running to a bus bar and the bus bar is running to negative chassis, then I do not need to use the grounding lug to chassis ground as the device would be grounded through the negative battery terminal given the internal connection.

This makes sense. In fact, I will take it one step further: If your DC negative is grounded elsewhere, you should NOT use the chassis ground or you will create a ground loop that could generate RFI noise.

Also, note that this means the AC Equipment Grounded conductor is connected to chassis either through the inverter ground lug or through DC negative. Consequently, you should avoid tieing the AC Equipment Grounding Conductor to the chassis elsewhere in the system.

 

[dsaint1884]

Connecting DC Negative to the chassis is unusual. I have not seen this on any other inverter. There is nothing 'wrong' with this I guess but it does mean the Battery circuit will be a grounded circuit whether you want this or not.

Agreed, I was going to ground it but I guess I don't even have the option now.

Consequently, you should avoid tieing the AC Equipment Grounding Conductor to the chassis elsewhere in the system.

Will do. Thanks for highlighting to make sure I'm thinking about it. I can just plug into the outlets in the front for AC and run no other ground anywhere at any point, it's all going out the inverter, through my DC negative and into the chassis to create a fault if one should ever occur. That's how I'm understanding it at this point anyway.

I appreciate your help and taking time responding to the thread.