Multi Family Feeder Wire size

[SoCalElectricalContractor]

I have read in 310.15 B6 that i can use this table for the wire size in a condo building. But, the engineers never use this wire size. Why? Also, up to what distance is 310.15 B6 good? I would assume it has it's limits but i can't find that anywhere. It truly irritates me when engineers ask for outrageous wire sizes when less will work for the customers.

 

[raider1]

I have read in 310.15 B6 that i can use this table for the wire size in a condo building.

Table 310.15(B)(6) can be used to size the service entrance conductors, service lateral conductors and feeder conductors that serve as the main power feeder to each dwelling unit for multifamily dwellings.

But, the engineers never use this wire size. Why?

That would be a design issue.

Also, up to what distance is 310.15 B6 good?

There are no distance restrictions to using Table 310.15(B)(6).


Chris

 

[charlie b]

I agree with Chris. Presuming you have the usual setup, with each unit having its own panel (only one panel per unit), then the conductors serving that panel can be sized per that table. If the engineers specify sizes based, for example, on Table 310.16, then I'd suggest submitting an RFI (or whatever process is used for getting design changes approved).

 

[SoCalElectricalContractor]

They use voltage drop calculations as well. Is there any issue with that?

 

[raider1]

They use voltage drop calculations as well. Is there any issue with that?

No, the NEC recommends that we take voltage drop into consideration when sizing feeders. Take a look at FPN No. 2 to 215.2.

Keep in mind that the conductor sizes listed in Table 310.15(B)(6) might not be large enough to keep your voltage drop to 3% or 5% so you might need to upsize the feeder, depending on the length of the feeder.

Fine print notes in the NEC are not enforceable as code but just for informational purposes only.

Chris

 

[SoCalElectricalContractor]

I can't find in the code book the formula for Voltage Drop. Also, will the calculation tell you to upsize it by 1 or will it tell you the minimum wire gauge?

 

[raider1]

I can't find in the code book the formula for Voltage Drop.

That's because the formula is not in the NEC.

Also, will the calculation tell you to upsize it by 1 or will it tell you the minimum wire gauge?

Depends on which formula you use.

HERE is a link to an on-line voltage drop calculator.

Chris