Load calculation multi unit

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alllen

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Hi, I am working on a load calculation for a 40 unit residential building. The units on average are 1000 square feet. They will have A/c, electric range, dishwasher , electric hot water tank and electric dryer. I have done many load calculations on a smaller level and I think I have this figured out but I'm looking for a little feedback and comparison. My main question is what size service do you come up with. I'm just looking for a rough estimate. Also is there any advantage to running 3 phase and then distributing off af that.

Thanks

Dishwasher 1.2 kva (10 amps)
Range 10 kw (40 amps)
Clothes dryer 5 kw (20amps)
Hot water tank 7000 watts
A/c 2 ton (approx. 12 amps)
 
Well I was on the phone last night with the architect and the Ranges and hot water tanks are going to gas. That should help with the load considerably. I'm coming up with a 1600 amp service? To big to small? Any input is appreciated. There will eventually be an engeneer on the job , right now were trying to come up with a rough estimate on the service costs.

Thanks
 
Volts Program

Volts Program

Okay I'm using the Volts program from a company named Dolphins Software.
I'm coming up with a protection size of 2500A for the feeder. And that's not even including the two small appliance circuits. It might help if you tell me a little more, i.e. voltage ratings etc.
 
Eric thanks for the reply, We plan on a 208/120 volt 3Phase 4 wire system. Let me know any more info you might need and I will round it up.

Thanks
Adam
 
I'm coming up with a real tight 1600 amp service by playing games with the calcs. 1600 amps is a little too tight for my comfort.
 
The disadvantage of running single phase 120/208 into each unit instead of 120/240 is that the dryer (and any other 208 volt load) will only draw 75% of the appliance rating so the dryer will take longer to dry the clothes
 
bsh said:
The disadvantage of running single phase 120/208 into each unit instead of 120/240 is that the dryer (and any other 208 volt load) will only draw 75% of the appliance rating so the dryer will take longer to dry the clothes
Click to expand...
Few people will even realize.
 
This is my first response to this forum. I have designing multi-family sevices for many years and am currently working on a project with 40 units, all electric, 1100 sf.
this senario comfortably fits on a 1600amp service

40units X 41.7 kva per unit
=1667.4 kva for service
X .28 (NEC 220-32-C)
=466.9 demand kva
=1297.7 demand amps @ 208/3ph
=3P-1600 main switch
 
Thanks for the responses

The dishwasher and A/c units will be in the apartments, There will be a community laundry room with 12 Wahers and 12 electric dryers. There will be no garbage disposols. There will also be built in micro wave ovens with exaust fans in them and also exaust fans in the bathrooms.

Thanks.

P.S
I also agree that 1600 will be tight
 
JRTman

Thanks for the info that makes me feel better about my calculations. Any idea's on how to hit the building. I will be working with the local utility. It will more than likely be overhead. I just finished a 800 amp three phase 4 wire service and have done quite a few over the years that size but this will be the first service I am involved in over 800 amps. Would we want to do two 800 amp drops to get our 1600 amps or would we do one large drop. Once i'm inside I plan on hitting a tap box or tap boxes and then having two 20 meter banks with breaker disconects for each and going from there to each apartment with ser. Thoughts idea's

Thanks
Adam
 
if your structure is a true building (not sub-divided with a fire separation wall), then you can only hit that building in one location. However, if you qualify under 2005 NEC 230.2- (c) - (Capacity Requirements) you could hit the building twice, as you are proposing.
what about house loads? elevators? amenity areas?
the sum of these loads could push your 1600amp service in excess of 2000amps,
thus qualifying for an additional service.

also, if you do hit the building twice and serve 20 meters @ each location, bare in mind that the demand calc for 20 meters is not simply 1/2 of the 1600a for 40 meters.
It will most likely require a 1200a service to each bank of 20 meters.
 
Clothes Dryer Calculation

Clothes Dryer Calculation

Okay, this will do for starters until I figure out how to apply this to the Volts program.

12 Clothes Dryers connected to 3-Phase 4-Wire

12/3=4 Clothes Dryers per phase

Multiply by 2 as in NEC 220.54. You get 8

8x5000W=40,000W.

Apply the Demand Factor for 8 dryers as in NEC Table 220.54

40,000X0.6=24,000W

But this load is for just two phases

Multiply 3/2 by24,000 and you get 36,000W for Three Phases
 
Allen, can you tell me more about the exhaust fans and microwave oven?
Do you want dedicated circuits for these appliances? And what about the hot water tank? Is every apartment to have one?
 
The microwave will be approx. 1200watts(over range type with exaust fan)This will be a dedicated circuit.
The hot water tanks and ranges were changed to gas
Bathroom exaust nothing fancy will be part of the 20 amp bathroom circuit.

House loads will be:

Elevator ( load unknown at this time I'm assuming atleast a 25 horse 208 3 phase motor )

Hallway lights 24 two buld flourescent fixtures T8 32 watt bulbs 1536 watts

8 outside wall packs 175 watt metal halide bulbs @ 208 volt

I will take a look at article 230.

Does anyone make a 1600 amp 3 phase disconect switch? or will I be into a breaker type piece of switchgear.

Thanks for the reply's
 
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