310.15 Residential

[gigawatt]

I am puting together a 600 amp residential service with 3-200 amp breaker type disconnects with 3 parallel 4/0 AL URD conductors from the transformer. The disconnects feed 3-200 amp panels in the residence. The service laterals pass through a CT can required by Holy Cross Electric in Colorado for metering. From the disconnects I am using 3 runs of 4/0 SER to feed the 3-200 amp panels as we have done for many years. My new inspector has recently stated that we will need 300 MCM wire to feed any 200 amp panel in a residence unless it is the only 200 amp panel on a 200 amp disconnect. What I would like to know is if you parallel 3-200 amp runs from the transformer and they go to 3-200 amp breakers which go to 3-200 amp panels then why does not this rule apply??

 

[Volta]

I am puting together a 600 amp residential service with 3-200 amp breaker type disconnects with 3 parallel 4/0 AL URD conductors from the transformer. The disconnects feed 3-200 amp panels in the residence. The service laterals pass through a CT can required by Holy Cross Electric in Colorado for metering. From the disconnects I am using 3 runs of 4/0 SER to feed the 3-200 amp panels as we have done for many years. My new inspector has recently stated that we will need 300 MCM wire to feed any 200 amp panel in a residence unless it is the only 200 amp panel on a 200 amp disconnect. What I would like to know is if you parallel 3-200 amp runs from the transformer and they go to 3-200 amp breakers which go to 3-200 amp panels then why does not this rule apply??

The laterals are outside: of the building, and probably the scope of the NEC, as they are utility conductors (or will be).

If you use SER then Section 338.10(B)(4)(a) sends you to Part II of Article 334.

Section 334.80 directs you to calculate the cables' conductors at 60 deg C.

Table 310.16 shows 60 deg Al 4/0 to be rated with an ampacity of 150. As long as the load on each panel does not exceed 190 amps, you can use 300 in SER. Or you can use 4/0 in conduit at 75 deg C and limit the loads to 180 amps.

 

[don_resqcapt19]

The reduced size conductors that are permitted in 310.15(B)(6) only apply to conductors that supply all of the dwelling unit load. When you have more than one disconnect the conductors that supply the individual disconnects do not supply all of the power to the dwelling unit and you can't use the reduced sized conductors. The conductors that supply multiple disconnects must be sized per Table 310.16.

 

[mcclary's electrical]

The reduced size conductors that are permitted in 310.15(B)(6) only apply to conductors that supply all of the dwelling unit load. When you have more than one disconnect the conductors that supply the individual disconnects do not supply all of the power to the dwelling unit and you can't use the reduced sized conductors. The conductors that supply multiple disconnects must be sized per Table 310.16.

Don wouldn't it matter what code cycle? Under 05' I think 215. (a) 3 allows him to do this

 

[mcclary's electrical]

On a side note, Do a load calc on the panels and if it comes in around 170-179 then you're good. They don't make a 180 amp breaker,,,,,so 4/0 al. would then be allowed to go on the next size up,,,,which happens to be 200

 

[augie47]

Don wouldn't it matter what code cycle? Under 05' I think 215. (a) 3 allows him to do this

I assume you are referencing 215.2(A)(3). I think it would be a real stretch to apply that to the size of a POCO service lateral.

 

[augie47]

On a side note, Do a load calc on the panels and if it comes in around 170-179 then you're good. They don't make a 180 amp breaker,,,,,so 4/0 al. would then be allowed to go on the next size up,,,,which happens to be 200

not in this area. here, 338.10, the 60? SE rating, trumps the other sections (I understand that is not a universal thought) so 4/0 AL SER would have a 150 amp ampacity. His inspector may be of like thinking.

 

[mcclary's electrical]

I assume you are referencing 215.2(A)(3). I think it would be a real stretch to apply that to the size of a POCO service lateral.

I'm confused,,,,I thought the inspector was questioning his feeders to inside

I now see what you're saying, and if I'm understanding you correctly, I agree with the inspector

 

[mcclary's electrical]

not in this area. here, 338.10, the 60? SE rating, trumps the other sections (I understand that is not a universal thought) so 4/0 AL SER would have a 150 amp ampacity. His inspector may be of like thinking.

We're on 05'

 

[augie47]

that does make a difference...wish we (still) were

 

[don_resqcapt19]

Don wouldn't it matter what code cycle? Under 05' I think 215. (a) 3 allows him to do this

I don't see how anything in Article 215 would apply. These are service conductors and not feeders. My comments apply to the conductors between the CTs and the disconnects, and also apply to the conductors between the utility transformer and the CTs, if these conductors are installed by the electrical contractor. If the conductors between the transformer and the CTs are installed by the utility, they are not covered by the code.