Service Entrance Conductor size

[Grouch]

I'm adding a new 1200 amp service switch, with 1000 amp fuses, tapping from an existing service point. there are 5 other existing service switches; with the 1200 amp SS, now we have 6 total service switches. All service switch ratings combined it's about 1500 KVA. This is in a multi-family building.

In the NYC amendments to the NEC, we have the following from section 230.42(A)(2):

Ampacity of the service-entrance conductors for services 1000 kVA and larger shall not be less than the sum of the maximum ampere ratings of the service disconnecting means.

Since I'm at 1500 KVA, I would have to comply with this statement.

Does this mean that my service entrance conductors, using copper, from the service point to the new 1200 amp SS have to be 3 sets of 600 MCM? that'll be a total rating of 420 x 3 = 1260 amps.

OR can I use 3 sets of 400 MCM, based on the 1000 amp fuse sizes; 335 x 3 = 1005 amps. But this would be less than the ampere rating of the 1200 amp service disconnecting means.

I do not know the service entrance conductor sizes of the other 5 service switches. So i don't know the total sum. So I believe by default I have to use 3 sets of 600's for the 1200 amp SS.

Am I interpreting this correctly?

 

[Tainted]

Found this 2018 Code Revision and Interpretation Committee Code Interpretation

https://www1.nyc.gov/site/buildings/codes/ecric-code-interpretations-2018.page



It hints you that you should size the feeders to the service switch frame size since it's more than 800A.

 

[Grouch]

Excellent. Thank you sir.

 

[Grouch]

I wonder, how did the person asking the question come up with the 800 amp threshold? There's no mention of 800 amps in that section at all.