parrallel conductors

[kimrichi]

in mike holt book NECexam preparation 2005 page 320 service neutral conductor size example where service conductor parralleled four conductors per phase [120/240] and the the service conductors are 250 kcmil should not the neutral be i/0 instead of 2/0
and one more thing please when allowiing service conductors in an enclosure with feeders do not we have same risk of bypassing feeder overcurrent in case of fault

 

[texie]

in mike holt book NECexam preparation 2005 page 320 service neutral conductor size example where service conductor parralleled four conductors per phase [120/240] and the the service conductors are 250 kcmil should not the neutral be i/0 instead of 2/0
and one more thing please when allowiing service conductors in an enclosure with feeders do not we have same risk of bypassing feeder overcurrent in case of fault

Assuming the use of copper. 4 X 250 KCMIL = 1000 KCMIL. Table 250.66 would indicate 2/0 copper for this. Why do you come up with 1/0?
Not sure I understand your second question.

 

[david luchini]

in mike holt book NECexam preparation 2005 page 320 service neutral conductor size example where service conductor parralleled four conductors per phase [120/240] and the the service conductors are 250 kcmil should not the neutral be i/0 instead of 2/0

1/0 would be the minimum allowable grounded conductor in each raceway per 250.24(C)(2). Does the example show a calculated neutral load greater than 600A?

 

[augie47]

as texie noted, the sum of your conductors per phase is 1000 kcmil. See Note 1 to Table 250.66, however check 250.24(C)(2) as the rule changes if you are using separate conduits for each set.
( I don't have that book the verify how they are installed)

 

[texie]

As Augie stated, it will depend it these are in separate raceways or not. When I said in my previous post that it would be 2/0 I was thinking of a single raceway. If the 4 sets are in different raceways, then I think the OP is correct, 1/0 would be correct per Art. 250(C)(2) (assuming you are looking for the minimum neutral and your load calc does not require more).
I need to be careful here as I am referring to NEC 2011 and the OP is using 2005. I know that there are some wording differences in this area from 2005 to 2011.

 

[kimrichi]

Assuming the use of copper. 4 X 250 KCMIL = 1000 KCMIL. Table 250.66 would indicate 2/0 copper for this. Why do you come up with 1/0?
Not sure I understand your second question.

do you design to have 4 phase conductors in same conduit in the example i refered to there was no derating for more than 3 carrying current so i thought it was chosen to be 2 parrallel phase conductors plus neutral with 250kcml that makes neutral to be 1/o