Uneven conductor quantity on paralleled supply-side interconnection

[andykee]

2000a/208v existing switchgear, with 400mcm Cu x 6 per phase from the utility to a 2000a main breaker.

PV Output to be interconnected - 350a, 250mcm AL x 2 per phase from a service rated disconnect.

If accepted by the utility & AHJ, the desired interconnection would be supply-side.

My initial thoughts would be to either:

1.) Tap 2 of the supply conductors from each phase with the 250's from the PV. - Issue being 4 of the other supply phase conductors are untapped.

2.) Use a suitably rated terminal block to accommodate all conductors from supply and pv to complete the tap. - Is there a terminal block rated for that high an ampacity?

Any thoughts on the above or other suggested methods welcome.

 

[jaggedben]

You should do (2). (1) could lead to the tapped conductors seeing an overcurrent.

See:
http://forums.mikeholt.com/showthread.php?t=189444
and
http://forums.mikeholt.com/showthread.php?t=170330

Terminal blocks for the appropriate size wire are rated for the appropriate ampacity, assuming wire meets the minimum size requirement for 75C rated terminals. I'd say you need an 8-position double-entry block for 400 MCM. They do exist.

 

[shortcircuit2]

Any provisions available for a load side interconnection?

 

[electrofelon]

A simpler option, if you get lucky, wold be to add lugs (or replace several existing with stack type to get more ports) to the switchboard. That would be the first thing I would investigate.

 

[ggunn]

2000a/208v existing switchgear, with 400mcm Cu x 6 per phase from the utility to a 2000a main breaker.

PV Output to be interconnected - 350a, 250mcm AL x 2 per phase from a service rated disconnect.

If accepted by the utility & AHJ, the desired interconnection would be supply-side.

My initial thoughts would be to either:

1.) Tap 2 of the supply conductors from each phase with the 250's from the PV. - Issue being 4 of the other supply phase conductors are untapped.

2.) Use a suitably rated terminal block to accommodate all conductors from supply and pv to complete the tap. - Is there a terminal block rated for that high an ampacity?

Any thoughts on the above or other suggested methods welcome.

With a 2000A bus and 2000A main OCPD, you may have enough electrical headroom to backfeed a breaker. Is (1.25)(your inverter nameplate Imax) < 400A?

 

[andykee]

Thanks

After a quick search I did find a sufficiently rated polaris block so that may be an option. A load side interconnection is also a possibility but due to the high cost of a suitable breaker the supply side connection is being explored.

 

[shortcircuit2]

If the CT's are after the 2000-amp Main...how will you net meter the installation?

 

[electrofelon]

A load side interconnection is also a possibility but due to the high cost of a suitable breaker the supply side connection is being explored.

Just a tip in case you weren't aware. Those large frame breakers bought by themselves are indeed super expensive. I always look on ebay and some of the online breaker suppliers. They presumably buy panelboards loaded with breakers to get the cheap "with panelboard price".

 

[texie]

Thanks

After a quick search I did find a sufficiently rated polaris block so that may be an option. A load side interconnection is also a possibility but due to the high cost of a suitable breaker the supply side connection is being explored.

I know Polaris makes blocks listed and rated for parallel runs but I'm not sure for this many conductors. Seems to me you need 6 in, 6 out plus 2 more for the PV input. Can you get these with 14 ports?

 

[jaggedben]

I know Polaris makes blocks listed and rated for parallel runs but I'm not sure for this many conductors. Seems to me you need 6 in, 6 out plus 2 more for the PV input. Can you get these with 14 ports?

By using an oversize block (say for 750mcm) you might be able to pass all the tapped conductors through the block and strip them without cutting and splicing. Then you could use an 8 port block. But I can't vouch from experience that this is practical for that many conductors, I've only done it for tapping 1-to-1.

electrofelon's suggestion about lugs is probably the first avenue to go down. Wish I'd said that.

 

[electrofelon]

By using an oversize block (say for 750mcm) you might be able to pass all the tapped conductors through the block and strip them without cutting and splicing. Then you could use an 8 port block. But I can't vouch from experience that this is practical for that many conductors, I've only done it for tapping 1-to-1.
.

Yeah, I think that would be the ticket, although I admit I haven't tried it either.