How to connect PV system in this CT cabinet

[PWDickerson]

The bussing where the CT's are doesn't look like it is rated for 800 amps. Do you know if it is?

How many inverters will be installed. If you have a multiple of 4 inverters, interconnecting at 4 points might solve some problems.

 

[jaggedben]

How large is the PV system compared with the panels fed from the bus in the CT can?...

He said the PV is 800A and each of the six panels is 200A. He didn't exactly say the conductors on the load side of the CTs are rated 200A each, though...

How many inverters will be installed. If you have a multiple of 4 inverters, interconnecting at 4 points might solve some problems.

Why does the number 4 matter?

 

[ggunn]

He said the PV is 800A and each of the six panels is 200A. He didn't exactly say the conductors on the load side of the CTs are rated 200A each, though...

Nevertheless, if he has multiple inverters he should maybe consider multiple points of interconnection if his AHJ will allow it.

 

[iwire]

The bussing where the CT's are doesn't look like it is rated for 800 amps. Do you know if it is?

How many inverters will be installed. If you have a multiple of 4 inverters, interconnecting at 4 points might solve some problems.

That looks like a 1200 amp CT cabinet to me.

 

[shortcircuit2]

Bump...sure wish posters would chime back in with end results...

 

[Solar_OR]

For an update:

Turns out that the 6 200A disconnects that were connected to the CT cabinet were all wired as 3 phase, but only connecting to single phase panels in the building. And on top of that, the electrician wired them all to only the A and B phases. So who knows how long there has been such a big imbalance at this site. In the end, we rewired all of the disconnects to balance out the system better and taking out the extra conductors freed up enough space to land the wires for the PV system. Still surprised with what I found out there some days, but it worked out for me in this case.

Thank you for all the input and suggestions.

 

[jaggedben]

Well that's an awesome anecdote and a good lesson in why one shouldn't skimp on the information gathering when looking to connect PV. Thanks for posting the followup.

 

[shortcircuit2]

What is feeding that CT Cabinet? Is that 2 sets of 350 MCM AL? What size transformer?

What size wires were feeding that CT cabinet?

 

[Solar_OR]

The utility ended up installing 3 sets of 350 MCM to accomodate for the solar.

 

[harborrick]

Distrubution Blocks

Distrubution Blocks

For all we know he put in a work order and the utility unlocked it for him. I dont see any issue with landing in the CT can as long as the POCO doesnt have a (silly) rule against it.

You should be able to find a burndy or Ilsco termination block to handle you backfeed wires.

 

[shortcircuit2]

The utility ended up installing 3 sets of 350 MCM to accomodate for the solar.

Thanks for getting back to me on that. It looked to me like 2 sets of 350MCM. So then did they up-size the transformer too?

 

[Solar_OR]

It was originally, and in the picture I posted, just 2 sets of 350 like you thought. The utility said they needed to install a 3rd set for the solar backfeed. Not sure on the thought process there since the service size did not change and neither did the transformer. Still puzzled on that one, but thankfully it was only about 15' of conduit so they did not charge too much and I just went with it to make everyone happy and get the job done.

 

[GoldDigger]

Simple: They added the VA historically delivered to the maximum VA which would be produced by the PV and just ignored that the two produced current in the opposite direction.

Or giving them more credit for intelligence they noticed that their wiring was set up for a continuous current far less than the nominal size of the service (justifiably based on historical usage) but that the PV by itself could deliver full current back to them for an hour or two, overloading their equipment in its present configuration.

 

[jaggedben]

Simple: They added the VA historically delivered to the maximum VA which would be produced by the PV and just ignored that the two produced current in the opposite direction.

Or giving them more credit for intelligence they noticed that their wiring was set up for a continuous current far less than the nominal size of the service (justifiably based on historical usage) but that the PV by itself could deliver full current back to them for an hour or two, overloading their equipment in its present configuration.

God I hope that utilities are smarter than to add the two together, although that might explain a couple delayed interconnections I've seen recently.

 

[shortcircuit2]

Simple: They added the VA historically delivered to the maximum VA which would be produced by the PV and just ignored that the two produced current in the opposite direction.

Or giving them more credit for intelligence they noticed that their wiring was set up for a continuous current far less than the nominal size of the service (justifiably based on historical usage) but that the PV by itself could deliver full current back to them for an hour or two, overloading their equipment in its present configuration.

Shouldn't it be a 300KVA transformer for the PV backfeed?

 

[GoldDigger]

Shouldn't it be a 300KVA transformer for the PV backfeed?

Yes and no, since this is POCO.

An "800A" PV system would require a corresponding service size under the NEC. But POCO can feed that service with as little equipment as they think they can get away with. The PV will not be producing full rated power for more than a few hours at a time and an oil bath transformer can handle overloads for a considerable period of time if they are allowed to cool back down again.

 

[electrofelon]

God I hope that utilities are smarter than to add the two together, although that might explain a couple delayed interconnections I've seen recently.

Lineman aren't always the best with their electrical theory. Recently I was hooking up a second service to a building with the POCO, and I expressed some concern about the size of the transformers on the first service because I had loaded it up pretty good and they only had half the NEC service size capacity up there. One guy does a quick calculation, without the 1.732, and says Im totally fine :angel:

 

[iwire]

Lineman aren't always the best with their electrical theory. Recently I was hooking up a second service to a building with the POCO, and I expressed some concern about the size of the transformers on the first service because I had loaded it up pretty good and they only had half the NEC service size capacity up there. One guy does a quick calculation, without the 1.732, and says Im totally fine :angel:

Has the transformer failed?

The lineman's knowledge aside the POCOs are pretty good about knowing what will work.


Our moderator Charlie E who was on the CMP for article 240 and a power company engineer has stated here that the power company he worked for assumes the real load of a building would be (and note the coincidence) about 40-50% of the NEC load calculations.

 

[jaggedben]

God I hope that the linemen aren't the ones making the utility engineering decisions.

 

[electrofelon]

Has the transformer failed?

The lineman's knowledge aside the POCOs are pretty good about knowing what will work.


Our moderator Charlie E who was on the CMP for article 240 and a power company engineer has stated here that the power company he worked for assumes the real load of a building would be (and note the coincidence) about 40-50% of the NEC load calculations.

I usually fully agree with that 40-50% figure. Whenever I get utility demand data, it always seem to be right in there compared to the service size. In this case, the 200A service and utility infrastructure was existing, then added onto so that the ACTUAL load was about 160 amps with 108 amps transformer nameplate. Probably OK for quite a while, but I generally dont go with the "it will work till the check clears" attitude......