Multiple raceways, does each need an EGC?

[ryangittens]

Hello, if you have one combiner box feeding multiple inverters, each with a separate raceway, does each raceway need an EGC or only one? Is there a code reference for this?

I think that only one is needed, but I wanted to make sure. The one EGC will take care of any ground faults from the combiner box and multiple EGCs would just carry fault current through other devices unnecessarily.

 

[Carultch]

Hello, if you have one combiner box feeding multiple inverters, each with a separate raceway, does each raceway need an EGC or only one? Is there a code reference for this?

I think that only one is needed, but I wanted to make sure. The one EGC will take care of any ground faults from the combiner box and multiple EGCs would just carry fault current through other devices unnecessarily.

View attachment 17968

Each raceway either needs an EGC sized to the largest circuit within, or needs to be the EGC.


Also, you cannot split up a combiner output circuit once it has been combined. If you have a combiner feeding multiple inverters, it would need to be a combiner with multiple zones. The most zones in a combiner I've seen is two.

 

[ryangittens]

I should probably fix that. It's actually a DC wire trough, that last one. And the wires from the previous combiner box just passes through the other. I'll be sure to add the EGCs for each. Thanks a lot!

 

[PVfarmer]

The most zones in a combiner I've seen is two.

Right. OP could use 1½ SMA CU-600s for instance, they have separate A and B outputs/zones.

But...doesn't using 1 combiner output for 3 inverter inputs defeat the purpose of each inverter having its own input and MPPT?

I also agree re: each conduit needing an EGG.

Here are some diagrams- each 3 string combiner seemingly has an EGC going out to an inverter.
http://www.midnitesolar.com/pdfs/MNPV2-3-4-6_manual.pdf

 

[ryangittens]

CLARIFICATION

CLARIFICATION

See the image below to more correctly show how it's installed.

 

[jaggedben]

You're new diagram looks good.

 

[ryangittens]

You're new diagram looks good.

iight thanks.. do you by chance know the reasoning behind why I must have an EGC in each conduit in this scenario?

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[jaggedben]

iight thanks.. do you by chance know the reasoning behind why I must have an EGC in each conduit in this scenario?

Aside from it being a subject to some very general code rules (see 250 Part IV and 300.3), you need to have an equipment ground connection to each inverter so that the ground-fault detection will operate properly. Lack of functioning fault detection could be catastrophic (i.e. greatly increase the chances of a huge fire). And you're not supposed to rely on some roundabout route through the AC side or something like that. That could perhaps result in voltage drop that compromises the ground fault detection, or it could increase the chances of a failure at a single point affecting everything. Basically the principle there is not to ask something to provide a function when the code requirements for it aren't based upon that function.

As Golddigger said, you are allowed to use a metal raceway as an EGC in many cases, provided it is bonded properly around fittings. 250.97 will apply in your case. So you don't necessarily need a wire EGC everywhere, although most people do it as good practice to provide redundancy even with metal raceways.

 

[ryangittens]

That point about grount fault detection is gold! Just brilliant. Thanks a lot for the answer my friend.

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[Carultch]

I should probably fix that. It's actually a DC wire trough, that last one. And the wires from the previous combiner box just passes through the other. I'll be sure to add the EGCs for each. Thanks a lot!

If you merge your circuits through a common wiring method, you can combine your EGCs such that you have just one EGC within that wiring method (sized to the largest circuit within). Then you need to diverge your EGC as you route the circuits to each inverter input. In any case, the egc path must follow the path of the corresponding circuit conductors.