xfmr secondary conductors

Status
Not open for further replies.
S

sparkytcc

Member
Location
Kamas, Utah, USA
I am installing temp. power to some office trailers for a jobsite. I was given a temp. power board that has 6 100 amp fused disconnects and a 150kva 480pri to 120/240 sec. installed on it. the sec. is all wired up with parallel 3/0 from the sec to a tap box with distribution blocks and 6 sets of 2awg from the distribution blocks to the indivdual disconnects. my question is if i used a 200 amp fused disconnect on the primary with 4/0 conductors does this violate 240.4(F) or is ok per 240.21(C)(2). note the sec conductors are less than 10ft. and the calculated load is 80kva. thanks for any info
 
sparkytcc said:
I am installing temp. power to some office trailers for a jobsite. I was given a temp. power board that has 6 100 amp fused disconnects and a 150kva 480pri to 120/240 sec. installed on it. the sec. is all wired up with parallel 3/0 from the sec to a tap box with distribution blocks and 6 sets of 2awg from the distribution blocks to the indivdual disconnects. my question is if i used a 200 amp fused disconnect on the primary with 4/0 conductors does this violate 240.4(F) or is ok per 240.21(C)(2). note the sec conductors are less than 10ft. and the calculated load is 80kva. thanks for any info
Click to expand...

240.4(F) doesn't come into play as the secondary is single phase 3 wire.

The #3/0 secondary conductors being "tapped" to supply the 6 disconnects is a violation of the last sentence of 240.21.

You could either run six individual sets of #2 from the transformer secondary, one to each disconnect, or you could install a 200A OCPD in the 3/0 conductors before the tap.
 
sparkytcc said:
sorry the info i was sent was incorrect the xfmr is single phase. so this is pretty much tapping a tap. right?
Click to expand...

Yes, you cannot "tap" from the transformer secondary conductors (it really doesn't matter if the transformer is single phase or three phase in this regard) per 240.21.

You would either need a 400A c/b to protect the 3/0 (I said 200 before, but I forgot you had parallel sets,) or you need an individual set of secondaries to each of the 6 disconnects.
 
Status
Not open for further replies.
Top