ground to neutral

[wwstrick]

I have an install that has had a few problems with its inverter. It burned out a communications card inside the inverter and now it appears to have done so again. The install is 16 270W modules in one string with a Solaredge SE5000 inverter. We are in Guatemala so there are no NEC rules and no inspections. The distribution panels (2) are home made with breakers mounted on DIN rail and a bus bar for ground and another bus bar for neutral. It is also a very high lightening area. The house has had one direct hit that cracked a cement wall. I was down there troubleshooting the inverter and decided to look closely at the house wiring. I could not find where the ground was connected to neutral. I checked both panels - nothing. I followed the ground wire a bit, but could find nothing. As part of the normal inverter inspection I had found 0V ground to neutral.

If there is no bond between ground and neutral, what would go wrong under normal use? or when lightening hits?

 

[Dennis Alwon]

The neutral and equipment grounding conductor's should be bonded together at the main pain- point of the first disconnect. You won't necessarily read voltage between neutral and ground but they should be connected. There is usually a strap or a screw that bond them together in the main panel.

 

[Buck Parrish]

I agree.
But if lightning hits it. It will likely melt the board, contactors and such. :happyyes:
We generally isolate the neutral and grounding conductor/electrode after leaving the first disconnect. It should help in case a part becomes energized for other reasons.

 

[wwstrick]

What I was asking is if the neutral is not connected to the ground at the first disconnect what sorts of problems might it cause? I have had some issues and I now know that they are not connected together. I will connect them. But what might it have caused to happen?

 

[GoldDigger]

What I was asking is if the neutral is not connected to the ground at the first disconnect what sorts of problems might it cause? I have had some issues and I now know that they are not connected together. I will connect them. But what might it have caused to happen?

If the ground wire is connected to any kind of earth electrode and the neutral is only connected to the POCO ground wire at the transformer it is possible for a lighting induced surge or nearby hit to drive enough current through the earth to develop an offset voltage between the two ground points. Without a metallic connection between neutral and EGC (grounding wire) at the house that voltage may get high enough to fry a circuit board that is mounted on a grounded surface but has one side of its power supply connected to the AC neutral.

If there is a ground rod or other ground electrode at the PV array and it is not wire connected to the EGC at the inverter you could have problems from that voltage difference too. (Mike Holt has a good video about separate ground electrodes on the DC side not connected to the AC EGC. A bad idea.)

 

[ggunn]

What I was asking is if the neutral is not connected to the ground at the first disconnect what sorts of problems might it cause? I have had some issues and I now know that they are not connected together. I will connect them. But what might it have caused to happen?

If the neutral is floating (not bonded to ground) on a split phase service, the line to neutral voltage will depend on the difference in loading between L1 to neutral and L2 to neutral. Theoretically, one or the other could approach 240V.

 

[pcanning87]

I'm curious, people who know more about this than I do - Does it ever make sense to add surge protection at a building main panel?


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[GoldDigger]

I'm curious, people who know more about this than I do - Does it ever make sense to add surge protection at a building main panel?


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Yes. The guiding principle is that for greatest protection against both conducted surges on the power line and lightning induced surges created within the building wiring there are two "best" locations for SPDs:

At the main panel or wherever the POCO service enters the building. This needs to be able to handle a lot of surge energy.
As close as possible to the equipment you are trying to protect (via outlet/receptacle SPD or power strip SPD). These need to handle whatever surge energy remains after (or because of) the building wire impedance. So smaller, but more of them.

For greatest protection, combine the two.

 

[cuba_pete]

I'm curious, people who know more about this than I do - Does it ever make sense to add surge protection at a building main panel?


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Yes. Most pertinent info is in the IEEE Green and Emerald and NFPA 780. Any SPD manufacturer usually has informative literature weighing the good and bad.

Lightning protection and surge protection can be defined as risk management and/or risk mitigation. There is always risk before and after, with or without suppression and/or protection systems.