Sizing conductors for Solar Interconnection Disconnect

[TKing92]

First post!

I'll keep this short. I've been installing solar for 8 years and have always followed a specific rule that has always been hearsay without representation in all my training. For this example, I'm installing a 200A Fusible disconnect which will be fused to 150A. When running conductors to the line side of this equipment, is it mandatory that the wire be sized to the equipment potential of 200A, or is it possible to size just to the 150A potential? I've always installed with the idea that too much isn't too much, but I've also never found this in the code book.

Any insight is appreciated!

 

[wwhitney]

Line side interconnection or load side interconnection?

If load side (of an existing service disconnect), the conductors on the utility side of the solar disconnect would need to comply with 240.4 with respect to the OCPD protecting them from the utility source.

If line side (of all existing service disconnects), the conductors on the utility side of the solar disconnect would be service entrance conductors and would need to comply with Article 230 like any other service. [Note that this was ambiguous under the 2017 and earlier NEC but I think the 2020 and especially 2023 NECs have cleared that up.]

Cheers, Wayne

 

[jaggedben]

The NEC allows the wires to be sized to 150A. For line side connections I've dealt with one utility and have heard of some others that would require 200A. Utility rule, not NEC.

 

[Eddie702]

If you have a 200A disconnect with 150 amp fuses the load wires only have to be 150 amp wires. The wires on the line side are determined by what is upstream of the disconnect.

 

[TKing92]

For clarity, in this scenario, the line side of this disconnect is fed from a transformer-fed CT cabinet. So my understanding is that because the maximum potential is limited to 150A, the conductors feeding the line side can be sized as such?

Thanks for your help, folks. Last question, just to be clear, there aren't any specific rules relating to this being a SOLAR interconnection disco, correct? Seems like there's always a lot more to learn about this line of work

 

[ggunn]

Seems like there's always a lot more to learn about this line of work

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