Multi-Family Dwelling Calculation

[BatmanisWatching1987]

The incoming service is 120/208/3 Phase

Each dwelling unit is about 1000 square feet with 100 Apartment.

All appliances will be Electric.

Would I need to add the Electrical Load for the Washer/Dryer under Calculated Load or under Application of Demand Factor

Please let me know if I miss calculated my Load Calculation for all 100 Apartments

 

[david luchini]

You need a laundry circuit per 210.11(C)(2) and 220.52(B).

If a dryer receptacle is included you need the dryer load per 220.54.

Is 8kW the actual Range nameplate rating at 208V?

Your values for Lighting/Small appliance load, and Range load for the entire 100 apartments don't seem right.


Why wouldn't you use the optional method? The total load would be less than half.

 

[BatmanisWatching1987]

For Laundry Circuit I added the 1500 W Load

For the Dryer I added a minimum of 5000 W but for the entire building I added the 25% Demand Factor based on Table 220.54

For the Range, I used 8kW since the local township looks for that amount for Electric Ranges

For the Entire 100 Apartments
Lighting/Small Appliance is taking the Total Load of 4,575 W and multiplying it by the 100 Apartments
Range, I used Table 220.55 with a 16% Demand Factor

Based on the updated Washer/Dryer, each apartment requires 150A breaker. Does this make sense based on the regular calculation

I just did the Optional Calculation based on 220.84 and I got 161A breaker for each apartment and the incoming 208V/3P is at 1,821A now compared to 5,481A


Does these updated Calculation make sense now for the Original and Optional Calculation based on the NEC Code

 

[Joe Villani]

A quick look at your individual unit optional method did you forget the first 10kva at 100 percent and the remainder at 40 percent? (AC would be in addition to this)

Also why is the laundry circuit missing (1500va) ?

 

[BatmanisWatching1987]

Based on Section 220.84, I don't see where it states you can use 10kVA for the first 100% and 40% for the reminder.

I was using Table 220.84, to use the demand factor of 23% since there are 100 apartments.


Thank you for noticing the missing 1500VA for the laundry circuit

 

[Joe Villani]

Why can't you use 220.82 for the individual dwelling unit feeder load?

Also is the water heater load that large? Just wondering.....

 

[david luchini]

Based on Section 220.84, I don't see where it states you can use 10kVA for the first 100% and 40% for the reminder.

I was using Table 220.84, to use the demand factor of 23% since there are 100 apartments.


Thank you for noticing the missing 1500VA for the laundry circuit

Not sure where you went wrong, but a 23% demand factor for (100) 33,500kVA units should be 770,500kVA, or 2140A

 

[BatmanisWatching1987]

@david luchini Thank you, I was missing the load for the Washer/Dryer.

@Joe Villani Based on what the Plumber gave me, he spec out a 6000W Water Heater. I just rounded up to the nearest whole number.

Also if I use Section 220.82 to size the individual dwelling unit feeder, I got appropriately 96 AMP. Please verify my calculation if you have the chance.


So in conclusion, I learned to use Section 220.82 to size individual feeders for each individual apartment/unit. Than use Section 220.84 to size total incoming service load for 100 apartments/units

My question now is, why is the incoming service load so high when using the Original Load Calculation Method (5,481 Amp) compared to Section 220.84 (2,140 Amp). The load was split in half completely.



Thank you again for everyone help/assistant.

 

[Joe Villani]

Please re-visit 220.82.

Note the heating and air conditioning is on its own in part C and cannot be lumped into part B.

Going from memory, the other day when i ran the calc i came up with around 116 amps, so it would be 125 amp feeder to the individual units.

Depending on your code cycle you can size your feeders based on 310.15(B)(7) based on the 125 amps.