Single family dewelling home. Changing from 100amp to 200amp service. I told them its overkill. They said maybe so,but its better then not upgrading enough and regretting it later .O.k so the question is sizing the service enterance conductors. 310.15 B-6 says #2/0 cu. So sizing the neutral i whent to 250.66 it says to use #4awg cu is this right??
200amp service upgrade.Sizing the neutral conductor question.
- Thread starter zappy
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JohnJ0906
Senior Member
- Location
- Baltimore, MD
zappy said:
Generally speaking, in dwellings, I size the neutral the same as the hots.
tonyou812
Senior Member
- Location
- North New Jersey
unless your situation strictly calls for copper then maybe you can save a few bucks downsizing the neutal.
iaov
Senior Member
- Location
- Rhinelander WI
This is something I've wondered about also. URD cable is sold with a reduced neutral. It was a question on my Masters exam but because I passed I never got to review the test and find out if I had the right answer. Like John, I generaly size the neutral the same as the phase conductors. Because of the input of members of this forum, I only use Al. now for SE cable and the cost difference for a full size neutral is too small to worry about. I guess my short answer would be 250.66 says you can use #4 Cu or #2 Al so it must be OK. I'm certain that if I'm wrong my learned collueges on this forum will enlightem me.:smile:
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
zappy said:
250.66 is for the GEC not the neutral, however art. 250.24(C)(1) does reference that the grounded conductor not be smaller than the required GEC in Table 250.66. That being said unless you can calculate the neutral load and determine a #4 is satisfactory I would not do this. I generally downsize one wire size for the neutral. Most houses have many 220 circuits that don' t demand a neutral so the grounded conductor load is almost always less than the ungrounded conductors.
iaov
Senior Member
- Location
- Rhinelander WI
Thanks again Dennis. I don't know why but I seem to be realy good at confusing the GEC with the grounding conductor.:smile:Dennis Alwon said:
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
iaov said:
Equipment Grounding Conductor- Table 250.122
Grounding Electrode Conductor- Table 250.66
Grounded Conductor- 250.24-- at least for some applications.
Edit to add: I often write EGC when i mean GEC and vice versa-- I have to slow down and think about it
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Most electricians will size the neutral two trade sizes smaller than the ungrounded as:
>That used to be a code rule (two trade sizes smaller)
>Triplex comes that way, such as 4/0-4/0-2/0 AL
Consider the neutral as a white wire with an imaginary green stripe. The white wire carries the unbalanced current, and the green carries fault current back to the source, IE the transformer, in the event of a line to case fault.
To use a 2 AWG AL cfor a 200 ampere service, base on 4/0 you would have to do a load calc. Most find it easier to go a couple of sizes smaller. If all the loads were 120 then it would require a much larger neutral.
>That used to be a code rule (two trade sizes smaller)
>Triplex comes that way, such as 4/0-4/0-2/0 AL
Consider the neutral as a white wire with an imaginary green stripe. The white wire carries the unbalanced current, and the green carries fault current back to the source, IE the transformer, in the event of a line to case fault.
To use a 2 AWG AL cfor a 200 ampere service, base on 4/0 you would have to do a load calc. Most find it easier to go a couple of sizes smaller. If all the loads were 120 then it would require a much larger neutral.
See 220.61 Feeder or Service Neutral Load.zappy said:
Feeder and service neutral conductors must have an ampacity large enough to carry the load as determined by this subsection. As far as I know, there is no other place in the NEC which permits for reduction of the neutral conductor ampacity.
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