What is the ampacity of this panel?

[Coppersmith]

I'm using NEC 2011.

I'm attempting to determine the ampacity of a MLO 3-phase panel (commercial). It is being fed by 1/0 CU THHN/THWN. The 4" feeder conduit goes underground to an electrical room several stores away. Since it goes underground I'm thinking I have to use the THWN at 75 deg which gives 150 amps. Not sure If I'm supposed to derate since there is 3 hots and a neutral in there (more than 3 CCC).

 

[infinity]

Is unlikely that you have 4 CCC'S for derating purposes unless more than 50% of the load is nonlinear. If there are no other adjustments required you should be at 150 amps.

 

[Cow]

I wouldn't count on wire size to indicate panel size. What if the engineer bumped the wire up because "it's from several stores away" and it's actually on a 100 amp breaker?

I'd find the breaker feeding it.

 

[Coppersmith]

I wouldn't count on wire size to indicate panel size. What if the engineer bumped the wire up because "it's from several stores away" and it's actually on a 100 amp breaker?

I'd find the breaker feeding it.

That's the next step. The panel itself is rated at 225 amps. I haven't gotten access to the electrical room yet to see what size the main breaker is.

 

[Coppersmith]

Is unlikely that you have 4 CCC'S for derating purposes unless more than 50% of the load is nonlinear. If there are no other adjustments required you should be at 150 amps.

Thanks, there is just a few motor loads from freezer, refridge and the RTU. Which code section talks about derating at >50% non-linear? I'd like to read it.

 

[Smart $]

Thanks, there is just a few motor loads from freezer, refridge and the RTU. Which code section talks about derating at >50% non-linear? I'd like to read it.

310.15B)(5)(c)

 

[Coppersmith]

310.15B)(5)(c)

Interesting. I'm always learning something new here.