load calc and generator sizing

[Electron_Sam78]

I've been asked to verify that a 40 KW generator will power a trailer set up as a commercial kitchen. Their load is

21 each 120v, 14 amp microwaves
3 each 120v, 7a freezers
1 each 120v, 14a Air Conditioner
existing lighting load of 120v, 10a

Total load is 40,680 VA

It looks to me that a 40KW generator will work fine especially after the demand factors are applied. Can anyone give me code references for applying demand factors and such?

An engineer said that the load has to be calculated by multiplying by 240v but I disagree since all the loads use 120v. If there were 240v loads then those would individually be calcualted and applied to the total.

 

[Electron_Sam78]

I've done some looking through the code book and the kitchen equipment gets a demand factor of 65% applied then the rest of the loads are at 100%

21 micros * 14a *120v = 35,280 * 65% = 23,000 W (NEC 220.56)
3 freezers * 7a * 120v = 2,520 W
1 AC * 14a * 120v = 1,680 W
lighting load 12ft * 50ft = 600 sq. ft. * 2VA/sq. ft. (NEC 220.12) = 1200 W
general receptacles: 20 each * 180 VA (NEC 220.14(I)) = 3,600 W

TOTAL = 32,000 W

 

[ceb58]

I've been asked to verify that a 40 KW generator will power a trailer set up as a commercial kitchen. Their load is

21 each 120v, 14 amp microwaves
3 each 120v, 7a freezers
1 each 120v, 14a Air Conditioner
existing lighting load of 120v, 10a

Total load is 40,680 VA

It looks to me that a 40KW generator will work fine especially after the demand factors are applied. Can anyone give me code references for applying demand factors and such?

An engineer said that the load has to be calculated by multiplying by 240v but I disagree since all the loads use 120v. If there were 240v loads then those would individually be calcualted and applied to the total.

You are correct, if you put ALL the load on one phase which would be in the 339amp range. The load will be split between two phases which will put you in the 169 amp range. Now by going with Sam's # allowing for demand it puts you in the 133amp range.

 

[mull982]

An engineer said that the load has to be calculated by multiplying by 240v but I disagree since all the loads use 120v. If there were 240v loads then those would individually be calcualted and applied to the total.

240V would be used to determine the maximum amount of current that can be passed through each leg. So for a 40kW generator (assuming resistive loading) there can be a maximum of 166.6A per leg. This means that you can have 166.6A of 240V loads across the two legs, or 333.3A of 120V loads split up on the two individual legs. (Each leg of generator is 20kW)