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Sizing Neutral #89780
10/19/04 04:02 PM
10/19/04 04:02 PM
S
sparkync  Offline OP
Member
Joined: Oct 2002
Posts: 830
NC
When sizing a neutral on commercial applications, can 70% be taken? I have a 100 amp. single phase sub panel fed by # 3 copper. What size neutral can I use? I tried to find it in the code, but can't seem to locate it. Can't seem to keep up with it all. Where can I find it in the code? I usually just run the same as phase conductors, but I may need to downsize if I can, to use a smaller pipe size. Thanks a lot. Steve

2017 / 2014 NEC & Related Books and Study Guides
Re: Sizing Neutral #89781
10/19/04 04:25 PM
10/19/04 04:25 PM
Y
Yoopersup  Offline
Member
Joined: Mar 2003
Posts: 849
Michigan
Try 2002 N.E.C. 220.22

Re: Sizing Neutral #89782
10/21/04 08:15 PM
10/21/04 08:15 PM
T
tdhorne  Offline
Member
Joined: Mar 2001
Posts: 345
Maryland, USA
Quote
When sizing a neutral on commercial applications, can 70% be taken? I have a 100 amp. single phase sub panel fed by # 3 copper. What size neutral can I use? I tried to find it in the code, but can't seem to locate it. Can't seem to keep up with it all. Where can I find it in the code? I usually just run the same as phase conductors, but I may need to downsize if I can, to use a smaller pipe size. Thanks a lot. Steve


Is this sub panel supplied from a single phase service or is it supplied from a three phase service. If the feeder is from a three phase service than the grounded current carrying conductor will carry just as much current as the phase conductors.
--
Tom Horne


Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison
Re: Sizing Neutral #89783
10/21/04 11:57 PM
10/21/04 11:57 PM
G
George Little  Offline
Member
Joined: Jan 2004
Posts: 1,498
Michigan USA
We need to know the load and type of supply to determine if you can reduce the grounded conductor. Some panels you can reduce the grounded conductor on three phase or single phase.


George Little
Re: Sizing Neutral #89784
10/22/04 08:05 AM
10/22/04 08:05 AM
Y
Yoopersup  Offline
Member
Joined: Mar 2003
Posts: 849
Michigan
The way I read it There can be no reduction in the Feeders & Service Neutrals till over 200 amps. Then after that 70% of the unbalanced load over 200amps, IF it meets the previsons of that section.And No reduction in some cases depending on type of service and type of loads.Such as an unbalanced Wye System.Some cases the Neutral Should be upsized.

Re: Sizing Neutral #89785
10/22/04 08:10 AM
10/22/04 08:10 AM
Y
Yoopersup  Offline
Member
Joined: Mar 2003
Posts: 849
Michigan
Also look at 250.24b1 for additional info on ungrounded conductor sizes.

Re: Sizing Neutral #89786
10/22/04 10:22 AM
10/22/04 10:22 AM
S
sparkync  Offline OP
Member
Joined: Oct 2002
Posts: 830
NC
The sub panel is fed from a single phase service. The load at this point will very little, about 30 or 40 amps, but I am supplying additional spaces for future expansion. It is a business which may add more equipment. I'm thinking I will go ahead and pull the same size neutral anyway to be safe. Thanks Steve

Re: Sizing Neutral #89787
10/22/04 10:47 AM
10/22/04 10:47 AM
R
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
Yoopersup,
Quote
There can be no reduction in the Feeders & Service Neutrals till over 200 amps.

Are you saying for feeders less than 200 amps the neutral must be the same size as the ungrounded conductors?
Don


Don(resqcapt19)
Re: Sizing Neutral #89788
10/22/04 11:05 AM
10/22/04 11:05 AM
Y
Yoopersup  Offline
Member
Joined: Mar 2003
Posts: 849
Michigan
Don
(Under cetain conditions) Yes, And sometime the Netural Should be larger then the ungrounded conductors.

Re: Sizing Neutral #89789
10/22/04 01:28 PM
10/22/04 01:28 PM
R
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
Yoopersup,
Then I don't agree with your statement. 220.20 only requires that the grounded conductor of a feeder be sized to the maximum unbalanced load. If this maximum unbalanced load exceeds 200 amps, then you only need to size the grounded conductor for 200 amps plus 70% of the unbalanced load greater than 200 amps. If you have a 120/240 volt panel where there is a one 20 amp single pole breaker and ten 2 pole 40 amp breakers for 240 volt loads, the ungrounded conductor could be 500 kcmil and the grounded conductor #12 and be compliant with the rules in the NEC.
Don


Don(resqcapt19)
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