AC Disconnect as a Combiner

H

hitehm

Senior Member
Location
Las Vegas NV
All - Please see the attached pic of the AC disconnect on this 3-line. This is for a 208/120 3P job we have pending. For reference, this is an Enphase system with two separate rooftop systems, each with it's own load center combiner panel. One has a combined output of approx 90A, the other approx 100A. The circuit designer took the outputs of the two AC combiners and combined them together on the input terminals of the 400A non-fused AC disconnect (circled in red). I personally have never seen this done and also couldn't find an AC disconnect with multi-wire terminals. They suggested we could use 3-port Polaris or similar splices to combine the 2 outputs into a pigtail to attach to the disconnect. This brings up several questions:

1) Are there any code violations or code language that addresses this? Since both the line and load side of the AC disco have OC protection, I don't see an issue there. As for ampacity, all of the wiring meets the ampacity requirements so I don't see any issue there either, including making sure the combined pigtail wire on the Polaris is sized to carry the combined current into the AC disconnect.

2) Has anyone done this before and if so, what listed hardware did you use to make the combined connection into the disconnect?

I know this probably seems simple but normally, if we needed multiple solar systems combined into a single source output, the plans would typically land each system's AC output onto individual breakers in an MLO load center that feeds the AC disco and onto the point of interconnection.


AC combined on disconnect.png
 
for piping, length, and placement requirements, you just need to make sure to abide by feeder tap rules in art 240.21(B).

as for sizing and all of those code references, you'd need to look under 430 (motors) for multiple motor feeders, or 440 (hvac/ref) for multiple loads.

keeping all of the wiring after that disconnect outside would certainly help.
 
hitehm said:
...

1) Are there any code violations or code language that addresses this? Since both the line and load side of the AC disco have OC protection, I don't see an issue there. As for ampacity, all of the wiring meets the ampacity requirements so I don't see any issue there either, including making sure the combined pigtail wire on the Polaris is sized to carry the combined current into the AC disconnect.
Click to expand...

I think this would be allowed. I agree that the tap rules could apply. There is language in 705.12 which addresses taps and which may require your taps to be larger and calculated around the 250A utility breaker plus the solar sources.

2) Has anyone done this before and if so, what listed hardware did you use to make the combined connection into the disconnect?
Click to expand...

Polaris or other listed multi-tap connectors like your designer mentioned would be fine.
 
I have seen a Single Line showing a disconnect being used as a combiner. I didn't win the project so I didn't have to worry about it, but I'm glad this came up and there are answers. I guess a Polaris could combine the two feeds into one feed as long as the combined side feeder excepts the upsized wiring, then use the disconnect as the OCPD. Hmm interesting way to avoid a full scale combiner panel and breakers.
 
You must log in or register to reply here.
Top