125% of load required for multifamily service?

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greenspark1

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Hi all. A basic question but one I haven't found clearly answered in the Code. Using 220.84 I calculated 850A load for a new multifamily project. Now to size the service, 230.31 (A) says to use the load calculated in Article 220. Easy, 850A. However, for underground services (which is what this will be), 230.42(A) requires 125% of continuous loads plus 100% of non-continuous. How does this requirement relate to 220.84, which doesn't differentiate between continuous and non-continuous and instead basically provides a blended diversity factor.

Bottom line, is 850A rated conductor/breaker Code minimum, or must I take 125% of 850A, or some other option? I feel that 850A conductors is acceptable.
 
RE: 125% of load required for multifamily service?

Anyone have a reply to this? At what point in the 220 calculations do you apply the continuous 125% factor? Before or after the 220.84 demand factor?

I ran across this same situation... Have a 14-unit multi-family with a seperate laundry center. 220.84 plus the house load gives me a demand of 488amps. If I use a 125% factor on the whole thing I get 610amps. However a multifamily would have a very small amount of continuous loads..

Would I be OK using a 600A rated circuit breaker for the meter stack?
Even if I estimated 50% of the load as continuous and 50% non-continuous, I would end up with 549Amps
 
greenspark1 said:
Hi all. A basic question but one I haven't found clearly answered in the Code. Using 220.84 I calculated 850A load for a new multifamily project. Now to size the service, 230.31 (A) says to use the load calculated in Article 220. Easy, 850A. However, for underground services (which is what this will be), 230.42(A) requires 125% of continuous loads plus 100% of non-continuous. How does this requirement relate to 220.84, which doesn't differentiate between continuous and non-continuous and instead basically provides a blended diversity factor.

Bottom line, is 850A rated conductor/breaker Code minimum, or must I take 125% of 850A, or some other option? I feel that 850A conductors is acceptable.
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If your calculated load is 850 amps then that is all you need. You need to pull conductors as large as the service you need. If you are going to use a 900 amp or 1000 amp service then the conductors must be sized for that.
 
Once you have calculated your non continuous and continuous loads then you would multiply by 125% for the continuous and add it to the non continuous load. Then divide by your voltage if single phase or your voltage x 1.73

There are very good examples of calculations in Annex D in the back of the NEC. In a MFD there really isn't much continuous load--IMO
 
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