res. service over 400 amp

[wyboy]

Can we use table Table 310.15(B)(6) and parallel conductors if the service is over 400? For instance, on a 1200 amp Res. Service can we run (3) 400MCM since one is good for a 400 amp service?

 

[chris kennedy]

Can we use table Table 310.15(B)(6) and parallel conductors if the service is over 400? For instance, on a 1200 amp Res. Service can we run (3) 400MCM since one is good for a 400 amp service?

Welcome to the Forum. Interesting question.

The table heading says 3-wire.

 

[Dennis Alwon]

Can we use table Table 310.15(B)(6) and parallel conductors if the service is over 400? For instance, on a 1200 amp Res. Service can we run (3) 400MCM since one is good for a 400 amp service?

If your service is rated 1200 amps then T310.15(B)(6) does not apply, IMO

 

[charlie]

If your service is rated 1200 amps then T310.15(B)(6) does not apply, IMO

I agree, the table goes up to 400 amperes . . . period.

 

[peter d]

Can we use table Table 310.15(B)(6) and parallel conductors if the service is over 400? For instance, on a 1200 amp Res. Service can we run (3) 400MCM since one is good for a 400 amp service?

1200 amp residential service? Are you wiring a castle by any chance?

 

[LarryFine]

. . . can we run (3) 400MCM since one is good for a 400 amp service?

Not in a single conduit.

 

[chris kennedy]

Not in a single conduit.

So if I use more than one conduit then this the install could use T315.(B)(6)?

 

[wirenut1980]

I would say if you wire each set of 400 kcmil copper to three separate 400 amp breakers/panels from a single main disconnect where all conductors are terminated, you could use the table. They would not be paralleled after the main disconnect, but I think it would work.

 

[480sparky]

I would say if you wire each set of 400 kcmil copper to three separate 400 amp breakers/panels from a single main disconnect where all conductors are terminated, you could use the table. They would not be paralleled after the main disconnect, but I think it would work.

Those would be branch circuits, not feeders. Then the table is out the window.

 

[wirenut1980]

1200 amp residential service? Are you wiring a castle by any chance?

Either that, or the house has a seriously sick home theater system.

 

[wirenut1980]

Those would be branch circuits, not feeders. Then the table is out the window.

I am interpreting the definitions in Article 100 for "feeder" and "branch circuit" to say that the conductors in question are feeders.

 

[C3PO]

I am interpreting the definitions in Article 100 for "feeder" and "branch circuit" to say that the conductors in question are feeders.

They are feeders, but none of them would be the "main power feeder" so 310.15(B)(6) does not apply.

 

[charlie]

1200 amp residential service? Are you wiring a castle by any chance?

We permit 1? residential services up to 1600 amperes but the load is not there. The Code requires a lot of additional size if the equipment is there but one family can't use it all at the same time unless it is Thanksgiving or a large party is in progress. A lot of people may increase the load for a short period of time but not for a long enough time to overload our transformer and secondary to the point of being undersized. It seems to me that a lot of ultra-large homes have multiple services to get lots of circuits and not for the load.

They are feeders, but none of them would be the "main power feeder" so 310.15(B)(6) does not apply.

I agree 100% :smile:

 

[LarryFine]

A lot of people may increase the load for a short period of time but not for a long enough time to overload our transformer and secondary to the point of being undersized.

What about the individual premises' service drop/lateral and entrance? They don't enjoy the utility's diversity during those times.

 

[charlie]

What about the individual premises' service drop/lateral and entrance? They don't enjoy the utility's diversity during those times.

The majority of the time, a home of this size will have their own transformer and the transformer secondary would be the service lateral. There is no diversity since there is only one customer; however, there is an extremely large amount of diversity in the use of power in the home. Even in the case of 10,000 to 15,000 square foot homes, a 75 kVA 1? transformer will work. We would install just two sets of 500 kcmil Al triplex service laterals to a 1,600 ampere residential service. Looking at the NEC, we are almost 1,000 amperes short of being able to serve the home but we don't have any problems.