exam question

Status
Not open for further replies.

ianis

Member
This Question came up ina recent exam:
" The following set of conductors are to be run in a rigid PVC conduit for a 347/600V . 3 phase feeder.
three #3/0 R90(xlpe)
one #3 R90(XLPE)
one #6 TW75 bonding conductor
What is the maximum ampacity rating of the feeder being fed by the three #3/0 R90 conductors"

Based on Table 2 CEC #3/0 is 210
210* .8=168 Amp

However the correct answer is 210. Based on how the question is put I still think the answer is 168. Am I missing something?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Does the CEC require derating for 3 current carrying conductors, or for 4 like the NEC? The next question would be if the #3 grounded (neutral) conductor is a current carrying conductor?
 

ianis

Member
CEC does not require a derating for 3 wires . The derating starts from 4 and up, however I believe a derating does apply when calculating the demand factor which requires a derating of 80% as per rule 8-104 . Afterall from what i understand they ask the max ampacity of the (appliance) using the #3/0. In other words if I have a 1440 W appliance at 120 V thats 12 Amps but the smallest conductor I can go with is #14 (15 Amps) that being 80% of the load.
Since on the question they didnt mention anything about the neutral being a curent carring conductor I am assuming that is not.
Thanks for the reply
 
Status
Not open for further replies.
Top