Ground Fault?

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bbartmasse r

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Washington State
Hello,

So we are installing an Outback Radian as a grid tied with battery system along with Outback Rapid Shutdown System.

One of the components of the rapid shutdown is a ground fault detection interrupter breaker, that gets connected to all sorts of sensors.

So I go to turn on the PV and the breaker immediately trips. I check wiring, everything looks good as far as I can tell.

I call Outback Tech. We go through all the wiring of the system, seems good. He sends me up onto the roof and has me check voltages.

I see 70.3 volts between PV+ and PV-, 0 volts between PV- and ground, and 67.2 between PV+ and ground.

He tells me this is my problem, I have a short somewhere. So I check each string, 5 of them. Every string shows very similar if not identical voltage readings, meaning every string has a short. At that point I say no way. The likely hood of this is too small and on top of that I wired it all myself, and it was done cleanly.

At this point I had to leave so couldn't do a lot more.

Any ideas? Anymore tests I could do to see where the problem may be? My gut tells me its still a mis wiring issue in the equipment somewhere or a bad breaker. But the tech was convinced it was a short at the array.

thanks for any suggestion
 
Isn't the Radian a negatively grounded system? If so you should see the same voltage between positive and ground as you see between negative and ground, when everything is hooked up. But the fact that you see a few volts difference does seem to corroborate a ground fault problem.

Ir order to identity the location of the fault you have to disconnect both positive and negative on any string as you test it to ground, or else you'll also be partly measuring the voltage to ground through the other strings, and not get accurate measurements of either.
 
When you turn on the inverter, the GFDI breaker trips off which means the negative is not grounded anymore. But you said you still read 0 volts between negative and ground, I suspect you have a bad negative PV wire somewhere in your system.
 
hill900505 said:
When you turn on the inverter, the GFDI breaker trips off which means the negative is not grounded anymore. But you said you still read 0 volts between negative and ground, I suspect you have a bad negative PV wire somewhere in your system.
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Or, equally likely, you have inadvertently made a bond between the common string negative bus and ground. This could also be fault in any one of the panels at the negative end of a string. A pinched wire is another possible source of the problem that hill indicated.
 
jaggedben said:
Isn't the Radian a negatively grounded system? If so you should see the same voltage between positive and ground as you see between negative and ground...
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Don't you mean that the positive to negative and positive to ground voltages should be the same? I agree that a small difference implies a high resistance ground fault somewhere other than in the negative home run. A pinched wire, maybe?
 
ggunn said:
Don't you mean that the positive to negative and positive to ground voltages should be the same? I agree that a small difference implies a high resistance ground fault somewhere other than in the negative home run. A pinched wire, maybe?
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Yes, I mistyped. Thanks, and I agree likely a pinched wire.
 
bbartmasse r said:
Why do I not see voltage between Negative and ground? Shouldn't I find the leaked ~4 VDC here?
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Either because you are testing with the GFDI breaker turned on, which bonds negative to ground directly, or because the fault is on a negative home run as hill90505 suggested.
 
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