Odd DC Circuit Breaker Wiring

[dynamictiger]

Hi

First off I am not an electrician so please forgive me for posting here. However I do work in the electrical related industry and am responsible for design of control boards, PLC programming and so on even though I am not qualified so I am not a total layman either.

Long story short my Solar PV system has issues relating to installation. After some enquiries I arranged for the power company compliance officer to inspect the site and he found several faults. I am awaiting their final report, but this particular thing had me curious.

One of the items found looked like incorrect wiring of the DC Circuit Breaker. The type is polarised. But my question is broader than that.

On the circuit breaker the DC positive from the solar array came into a connection point on the circuit breaker and in the same connection point there was a cable connected back to the earth bar. This as I understand it and as shown by the inspectors meter is effectively taking the solar output to earth.

Besides the fact this makes no sense to me whatsoever, is there some reason you may wire a DC circuit this way? Has the installer wired the circuit breaker like an isolator, a common fault I understand?

Sorry I am just curious. Thanks for looking.

 

[augie47]

( I allowed this post even though the poster advises he is not in the trade. His post is asking for an explanation and not, IMO, a DIY post)

 

[GoldDigger]

It is certainly possible that the system is wired up for positive ground on the array. Where does the array negative connect?
At least one line of solar panels will not work unless the positive end of the string is grounded. That then requires an inverter that accepts positive ground.

Also, for a nominally ungrounded array, what you see may actually be part of a ground detection circuit.

To give more accurate information would need a complete wiring diagram and the part numbers on the components.

Tapatalk...

 

[dynamictiger]

Thanks very much for the response, and I appreciate you letting me post. No I am not a DIY. I actually know enough to also recognise my limitations and DIY is not something I would attempt.

Thanks for the thoughts on the positive ground. I hadn't thought of that, I was only looking over the shoulder of the inspector and noted it as odd in my eyes. Just wanting to understand the reasoning. It seemed wrong to me and the inverter manual Fronius IG 30 Outdoor does not mention positive grounding so I think it is erroneous. I just wondered if it was something to do with the polarised / non ploarised / circuit breaker / isolator conflicts I have been reading on. Thanks.

 

[GoldDigger]

Are the panels from Grape Solar? They were the largest maker of panels that required positive ground.
If the circuit breaker is correctly wired for polarity, it would have to be reversed if in the negative lead.
Use of polarized circuit breakers for connection to a charge controller is more of a problem, since the only time the breaker could ever open under overload would be from reverse current from the battery resulting from a double fault. But the manual opening of the breaker under load would happen with forward current.
For a PV to GTI disconnect, the right direction to install it is more obvious.


Tapatalk...

 

[dynamictiger]

The panels are Sunpower. The manual does say Sunpower modules must only be used in configurations with galvanic insulated inverters where the positive polarity of the PV array is connected to a ground protected by a fuse. For more information visit www.sunpowercorp.com/inverters but that link doesn't work. The direct connection to the circuit breaker and earth bar, no inline fuse, positive reading on volts at the earth bar and this and your information are suggesting this is not correct. Another bloody error. Thanks very much for your help.

 

[jaggedben]

Sunpower does require positive grounding. For a grid-tied system this should be done through the ground-fault fuse in the inverter, as your manual describes, and that is the only place it should be done. The arrangement you describe definitely sounds like an error, probably with the installer not realizing how the ground-fault system works and thinking he needed to ground the array with a field connection. If the installer did not connect the ground terminal in the inverter to ground, then your grounding wire needs to be moved from the circuit breaker to that location.

Although it doesn't sound like your situation, in a off-grid system it might be appropriate to have a solid, unfused connection to ground. The code here in the States wouldn't allow that anymore, although some think it's a good idea.

 

[dynamictiger]

Sunpower does require positive grounding. For a grid-tied system this should be done through the ground-fault fuse in the inverter, as your manual describes, and that is the only place it should be done. The arrangement you describe definitely sounds like an error, probably with the installer not realizing how the ground-fault system works and thinking he needed to ground the array with a field connection. If the installer did not connect the ground terminal in the inverter to ground, then your grounding wire needs to be moved from the circuit breaker to that location.

Although it doesn't sound like your situation, in a off-grid system it might be appropriate to have a solid, unfused connection to ground. The code here in the States wouldn't allow that anymore, although some think it's a good idea.

Thanks once again this is making more and more sense now.

The DC circuit breakers were replaced due to corrosion. Post replacement, whilst still under repair the inverter started to smoke. The original installers, refused warranty on the inverter due to age. However when I kicked up a stick saying come on you were here fixing it and blew it up, they wrote back via a lawyer. When I saw this response I started to look for what else they were trying to cover. When I started to look at the install properly I found numerous errors. Eventually my power compliance inspectors got interested and this is where I saw this fault. I now suspect this is what would have caused the inverter to start smoking to begin with...However in the overall scheme of things this is minor compared to other faults and errors now unearthed. I was just curious on this one as it seemed to me a no brainer.