electricblue
Senior Member
- Location
- Largo, Florida
- Occupation
- EC
Where is the 70% neutral de-rate in the code? Is it just for a service or can it be for feeders too?
neutral derate?
- Thread starter electricblue
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
In general the service grounded conductor can be sized as small as the gec but for service conductors larger than 1100kcm copper or 1750Kcm Al
250.24(C)(1) states 12.5%.
Feeders--- the neutral cannot be smaller than the egc. 215.2(A)(2)
250.24(C)(1) states 12.5%.
Feeders--- the neutral cannot be smaller than the egc. 215.2(A)(2)
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
That is for demand factor for specific loads
So if I have a service with a 4/0 alum ungrounded conductor, my nuetral can be a #4 cu.? :happyno:
Isn't that what the OP asked for? The 70% deration on the neutral? 220.61 is for Feeder and service neutral load.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
If the calculated load is not greater than a #4 then :happyyes: Did you read 250.24(C)(1)
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Yes he asked about 70% derating but I have a suspicion that there is confusion with that section you quoted.
Oh yea, calculated by..........220.61:roll:
Sure. It tells me that the neutral doesn't have to be larger than the largest ungrounded conductor, and cannot be smaller than the required GEC per table 250.66. But the actual size of the neutral must come from 220.61. No?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
You better read that section if you want to use it for a 200 amp service-part 2 says for unbalanced loads in excess of 200 amps where the service is fed from .....
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Yes but not the 70% part in part (2) at least not in all cases. I think that section is confusing at best. Many ec's state that they can downsize 70% of the ungrounded conductors-- that is not the case across the board. I made assumptions that the OP was not thinking of this but I may be wrong.
That portion of the unbalanced load in excess of 200
amperes where the feeder or service is supplied from a
3-wire dc or single-phase ac system; or a 4-wire,
3-phase, 3-wire, 2-phase system; or a 5-wire, 2-phase
system
OK...
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Does a 200 amp service have an unbalanced load of 200+ amps. This applies when the unbalanced load on the neutral is more than 200 amps-
220.61 has to be read as a whole, then used in applicable parts.
220.61(B)(1) I would use on a 200 Amp house service.
220.61(B)(2) I would use on a much larger service, along with any other applicable parts of 220.61.
If my calculated neutral load came to be very low, or if my ungrounded conductors needed to be very large, then I would look at 250.24 and 250.66 also.
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