NEC Article 280.84 Multifamily Dwellings

[Robert G. Morrissey]

Aloha,

We have four single family homes being fed from a single utility feeder. Can I use Table 220.84 Optional Calculations for calculating the Demand Factor for four dwelling units? Or must I use Article 220 Part III?

Thank you

 

[jtester]

I am confused about your question. Are you a utility designer? The NEC would not apply to a utility system feeding homes, but would to the wiring if the utility required the Owner to connect at the transformer, for example.

Jim T

 

[George Stolz]

I agree with Jim. I'm not seeing it. Can you describe your situation in more detail?

Four houses are not a multifamily dwelling.

 

[Robert G. Morrissey]

Thank you for your responses. We are running an underground service from the secondary of the utility company's transformer to four single family houses (connecting at each house's WHM). The designer used Table 220.84 Optional Calculations and chose a Demand Factor of 45%. I feel he should be using Article 220 part III to calculate Demand Factor.

 

[George Stolz]

Honestly, the most conventional answer would be to go see the utility, and see what the NESC has to say about the sizing of the conductors.

The section the designer used would not apply; but full-sized conductors according to the NEC would be excessive, as far as standard utility practice goes. There is an accurate, efficient answer, but it can't be had from the NEC, IMO.

 

[jtester]

George is right, 220.84 doesn't apply. However

We are running an underground service from the secondary of the utility company's transformer to four single family houses (connecting at each house's WHM)

Who is "we"? Where I work, one utility requires the customer to run conductors to the transformer on commercial projects. The customer has to size them to Article 220, because he owns them. Another utility runs to the customers meter, and it would be irresponsible for them to use 220 to size the conductors.

The application of Article 220, in this case, depends on whether you are working for the utility, or for the builder or owner.

Jim T