Calculating branch loads

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Bjenks

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East Coast of FL
23 apartments from a 1923 building are each served by one 30A 240V and one 20A 120V fused circuit. Each apartment's 240V circuit has a Water Heater 1500 W & Stovetop 840 W. Which has no problem with a 30A circuit.

However, the 120V circuit has an AC Unit 5.2A, Microwave 6.66A, Refrigerator 3.75A, and Receptacles/lighting calculation at 3VA/SQ of 11.51A. With multipliers it comes out to 28.4A total for the wire size.

This obviously exceeds the 20A rating of the #12 wire. So when I asked the customer about this she mentioned that they don't have any problems with blown fuses. My question is how do you do the load calculation on these units without making them run another circuit to each unit? Because of other code issues the county has come in and red tag any future electrical till a load cal has been done for everthing in the building.
 
It sounds to me like the only way to get a straight answer on this is to sit down with the AHJ and the owner to work all this out before hand.

I have done quite a few service up grades in 25 to 35 unit apartment buildings that we installed a complety new service sized to todays standards but left the original 15 amp 120 volt riser to the units.

This was an imediate problem as they all had 30 amp fuses in them when we got there and 15 amp breakers when we left. Obviosly the 15s where triping. I really don't know how that issue was resolved as it was outside our scope of work.

That said I think that was a very odd situation only allowed due to local rules that prohibit the inspector from applying the NEC retroactivly.

In most areas I aimagine you will have to upgrade the units which is going to get expensive really quickly.

It could be good for you as long as the project is not canceled.
 
Back in the late 70`s in NYC we did what was called an adequate wiring upgrade from a single 15 amp fuse that was in the basement to a 60 amp panel usually mounted in the dumb waiter shaft.
One 60 amp sub panel
Two 15 amp lighting circuits (split the one into two)
one 20 amp a/c receptacle
one 20 amp kitchen receptacle usually the fridge.

Damage was minimal,It passed all the time.Guess it was the lesser of 2 evils.
 
Bjenks said:
23 apartments from a 1923 building are each served by one 30A 240V and one 20A 120V fused circuit. Each apartment's 240V circuit has a Water Heater 1500 W & Stovetop 840 W. Which has no problem with a 30A circuit.

However, the 120V circuit has an AC Unit 5.2A, Microwave 6.66A, Refrigerator 3.75A, and Receptacles/lighting calculation at 3VA/SQ of 11.51A. With multipliers it comes out to 28.4A total for the wire size.

This obviously exceeds the 20A rating of the #12 wire. So when I asked the customer about this she mentioned that they don't have any problems with blown fuses. My question is how do you do the load calculation on these units without making them run another circuit to each unit? Because of other code issues the county has come in and red tag any future electrical till a load cal has been done for everthing in the building.
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If i understand this right they are running frig ,ac, all lights,toaster,mr coffee.tv,radio ,computer,hair dryer,etc all on one 20 amp circuit.Must be a fantastic penny under that fuse.Not saying if i had to make do with this i could not live but it would require the green acres method.
 
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