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Multi-family load calculation question

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K

KBot9

Member
Location
NYC
Occupation
Contractor
Say an existing 200 unit building has determined the existing maximum demand for the entire building via a years worth of utility statements and metering at 1500 Amps

They seek to add three circuits per unit : Laundry, Dryer, and electric range.

Can the calculation be :

Starting with the existing max demand load of 1500 amps then as per 220.87 times 125% (The calc satisfies all 3 caveats of 220.87) so 1875 Amps.

THEN, add the three new proposed devices, calculating their total demand per either via 220.42/54/55 or 220.82 or 220.84 and plug in and to existing max (plus 25%) 1875 Amps whichever of those three options are lowest?
 
JoeStillman

JoeStillman

Senior Member
Location
West Chester, PA
220.87 requires 125% of the existing measured demand, but I would not add the 25% to the new loads. You wouldn't consider these continuous in a new building calc.

Assuming the service is 3Ø, per 220.54 and 220.55 "Where two or more single-phase [dryers or ranges] are supplied by a 3-phase, 4-wire feeder or service, the total load shall be calculated on the basis of twice the maximum number connected between any two phases." Then your adjusted quantity is not 200 appliances, it's 134. (You have 66 on A-B, 67 on B-C, and 67 on C-A, 67 x 2 = 134)
 
K

KBot9

Member
Location
NYC
Occupation
Contractor
JoeStillman said:
220.87 requires 125% of the existing measured demand, but I would not add the 25% to the new loads. You wouldn't consider these continuous in a new building calc.

Assuming the service is 3Ø, per 220.54 and 220.55 "Where two or more single-phase [dryers or ranges] are supplied by a 3-phase, 4-wire feeder or service, the total load shall be calculated on the basis of twice the maximum number connected between any two phases." Then your adjusted quantity is not 200 appliances, it's 134. (You have 66 on A-B, 67 on B-C, and 67 on C-A, 67 x 2 = 134)
Click to expand...


Yes the dryer and ranges would be calculated that way for 220.42.... but in 220.82 & 84 it says "nameplate" added to total then each's demand factor.(In this case with 100 units it would be nameplate total where first 10kW is 100% and balance at 40%.... OR 220.84 where it's nameplate total times 23% .)

No? No mention in 220.82 or 84 referring to using method in 220.54/55 or specifically mentioning the 1P loads o 3P feeders calc.

.... or Am I to use the 'single phase on three phase feeder max connections to table then /2 * 3' thing regardless for the new load only ?

But yes My general question is I take the existing and add 25% per 220.87... THEN can I use either 220.42 or 82 or 84 for the new proposed load and add the two totals? (I dont add the 25% to the new load, I get that part.)
 
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