Wire size for an 800 amp serice (paralled)

[tadavidson]

I had an ol' friend and 30 year electrician who is now 49% owner in a GA. company that does a lot of work in NC at distribution hubs ask me about wire size to the service. I sent him to table 310.15 and the 75 degree column. It was different that the prints had specked for the run 600MCM vs 500mcm. Where was my error.

 

[iwire]

I had an ol' friend and 30 year electrician who is now 49% owner in a GA. company that does a lot of work in NC at distribution hubs ask me about wire size to the service. I sent him to table 310.15 and the 75 degree column. It was different that the prints had specked for the run 600MCM vs 500mcm. Where was my error.

Two sets of 500 is under 800 amps it takes two sets of 600 to use an 800 amp breaker.

Keep in mind at 800 amps or more 240.4(B) does not apply and you cannot round up

 

[tadavidson]

Two sets of 500 is under 800 amps it takes two sets of 600 to use an 800 amp breaker.

Keep in mind at 800 amps or more 240.4(B) does not apply and you cannot round up

Yes, my direction was 600mcm. The stamped prints were 500mcm. I told him it was his responsibility to do the right thing regardless of the prints. IS there also any derating for more that 3 current carrying conductors in a raceway? Three phases and Neutral?

 

[electrofelon]

I had an ol' friend and 30 year electrician who is now 49% owner in a GA. company that does a lot of work in NC at distribution hubs ask me about wire size to the service. I sent him to table 310.15 and the 75 degree column. It was different that the prints had specked for the run 600MCM vs 500mcm. Where was my error.

Only thing I can think of other than a mistake is it is a service with multiple service disconnects which would allow the wire to be sized to the load (in that case it shouldn't really be called an 800 amp service but if it was a panelboard with an 800 amp bus one might call it an 800).

 

[tadavidson]

Only thing I can think of other than a mistake is it is a service with multiple service disconnects which would allow the wire to be sized to the load (in that case it shouldn't really be called an 800 amp service but if it was a panelboard with an 800 amp bus one might call it an 800).

I do believe it was one to 800 amp OCPD.

 

[augie47]

Two sets of 500 is under 800 amps it takes two sets of 600 to use an 800 amp breaker.

Keep in mind at 800 amps or more 240.4(B) does not apply and you cannot round up

I beg to differ 240.4 allows "round up" fro 800 amps or less.
If the calculated load is 760 amps or less, he can use the 500s (assuming separate conduits)

(In the somewhat rare situation that he has to count the neutral as a ccc then the allowable load would be 688)

 

[iwire]

I do believe it was one to 800 amp OCPD.

In that case I agree with you 600 would be required.

I think this really comes back to people knowing they can use one set of 500s for 400 amp OCPDs so they figure two sets of 500s get them to an 800 OCPD.

 

[tadavidson]

I beg to differ 240.4 allows "round up" fro 800 amps or less.
If the calculated load is 760 amps or less, he can use the 500s (assuming separate conduits)

(In the somewhat rare situation that he has to count the neutral as a ccc then the allowable load would be 688)

To be clear, the citation you mention allows that if the calculated load for this operation is say 760 amps to use conductors rated at 760 amps but connect to an 800 amp OCPD?

 

[tadavidson]

(In the somewhat rare situation that he has to count the neutral as a ccc then the allowable load would be 688)

What makes the situation "rare"?

 

[infinity]

To be clear, the citation you mention allows that if the calculated load for this operation is say 760 amps to use conductors rated at 760 amps but connect to an 800 amp OCPD?

Yes.

In that case I agree with you 600 would be required.

I think this really comes back to people knowing they can use one set of 500s for 400 amp OCPDs so they figure two sets of 500s get them to an 800 OCPD.

As Augie noted 2 sets of 500 kcmil can be used with an 800 amp OCPD via the next standard size rule. Over 800 amps cannot use the next size up rule.

 

[augie47]

What makes the situation "rare"?

In order for the neutral to be counted as a current carrying conductor a major portion of the load would have to be non-linear". Does not happen a lot on services.

 

[Carultch]

Keep in mind at 800 amps or more 240.4(B) does not apply and you cannot round up

800A and less = you can round up. 800A inclusive.
Over 800A = you need as much wire amps as OCPD, no matter what

 

[iwire]

I beg to differ 240.4 allows "round up" fro 800 amps or less.

As Augie noted 2 sets of 500 kcmil can be used with an 800 amp OCPD via the next standard size rule. Over 800 amps cannot use the next size up rule.

800A and less = you can round up. 800A inclusive.
Over 800A = you need as much wire amps as OCPD, no matter what

Wow guys, you all need to keep up with the latest changes.

 

[Smart $]

Wow guys, you all need to keep up with the latest changes.

Some changes cross all boundaries. Some don't. That's one of the latter.