Utility Service Sizing

[saladhawks]

I am curious if anyone has heard of sizing Utility Transformers & Conductors from Service Panel Sizes?

For example, if a 2400V - 120/240V, 1-Phase stepdown utility transformer will service five houses with 200A, 120/240V, 1-Phase, 3-Wire Serive Panels, would it be possible to size the service transformer and conductors with just this information (square footage of houses are not available).

If so, what type of "design" factors would be recommended?

 

[wareagle]

Utilities have done studies that have produced a demand factor for homes with different loads. Example
House with lts, ref, range, dryer wh, 3T A/C will produce
a certain demand. 4 houses produce a certain demand. I believe it is done more with the actual load rather than the size of the main panel.

 

[tommom]

There is some very good info on residential load estimation and demand in the Westinghouse Distribution Reference Book vol. 3 (vols 1 and 2 were never published.) It's a little old, but the general principles still apply.

 

[BJC]

Most utilites have application guides for sizing transformers. I know that Puget Sound Energy, Portland General Electric, Pacific Gas and Electric and Souther Cal Edison. have them. Weather or not they will give them to you depend on who you talk to. I have had copies of all of them I got from engineers at the above utilites so there not secret.
Of the four above they vary with climate. They all vary with square footage and the type of heating ( gas or electric) and type of water heaters.
The NEC has some (Sec 210 or their abouts) you can use.
I am traveling and don't have the exact section.
You don't have to have the exact square footage if you know the type of developement ( small house or McMansions).

 

[apowerengr]

Homes typically range from 3-8kW "coincident" demand which is what utilities will use to size their service transformers. Non-coincident demands would be used to size service conductors for volt drop and losses.

 

[jghrist]

Service size will be of little use for residential load estimating because 200A services are pretty much standard for even smaller homes.

I have an old SDG&E guide for commercial loading that uses service panel sizing as one estimating means with a different % for different types of businesses, ranging from 25% to 48% of service panel size. This would be of no use for residential, however.