apartment load calculation

[jimingram]

I have a 30 unit '60s vintage apartment building with an 800 amp, 1ph, 120/240 volt service. Each unit has an individual 60 amp feeder from a meter bank.

Each unit has a window AC(5.9amp,240v), electric range(10KVA), and a garbage disposal(6amp).

There are 22 units at 900 sqft, 8 units at 1200 sqft. The house panel comes from the main service.

The house has three washers and four gas dryers in the laundry room. There is a central hot water boiler with a circulation pump (typical for Minnesota).I calculate the house load
with the above items and common lighting at 75 amps.

The owner wants to remove the disposal and install a dishwasher (10amps) in each unit.

I used the optional calculation for a multiunit occupancy and came with 821 amps for the existing load. There has been no problem with the service handling the load over the years.

If I replace disposals with dishwashers the load would be 840 amps. I would also have problems with the unit feeder (62amps) with a dishwasher.

I'm looking to see if dishwashers with no electric heaters are available. Even with that the calculated load is right at capacity. the inspector will be looking at my calculations very closely so I want to be accurate.

Any suggestions would be helpful.

Jim

 

[charlie b]

Re: apartment load calculation

Another approach you could try is to perform a 30 day load test, or to gather one year's worth of utility bills. If the actual load, as measured in one of these two ways, plus 25% of that measured load, still leaves room to add the dishwasher load, then you can use 220.35.

By the way, a dishwasher that did not include a heater would not be effective in cleaning and sanitizing dishes. I would not count on that solution.

 

[bphgravity]

Re: apartment load calculation

I would use the Existing Dwelling Unit calculation to figure the feeder load to each unit per 220.83. This calculation would permit the 60A feeder.

Also, when I calculate the service load based on your information and 220.84, I only show a load of 790A. I completely feel your existing installation can stay as is.