calculation for apartments

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manny

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I want to find out how a electrical contractor figure out that 2/0 wire is the correct wire size for A meter bank that has 4 meter base. Each meter has 100amp disc..and each disc...feeds a main lug panel, This is for a remodel building..I what to know were he came up with this size of wire..thus the power company help contractors figure out the demand loads for services on remodels. Or the city building inspectors help out the contractors figure..

bphgravity

Senior Member
Re: calculation for apartments

It usually is not the responsibility of the utility company or the building department to assist contractors on load calculations. They may enforce certain requirements and assist in meeting those, but the calculations are well within the scope of the contractors responsibilty. Service calculations are found in Article 220 of the NEC. The code allows certain amounts of total load reduction when sizing the service and service conductors. These reductions are called demand factors. The basis of these demand factors are that while the individual branch circuits will see the total connected load of the equipment they serve, services will most likely not. For example, what are the chances that all 4-apartments will have their ranges on full heat, the dryers going, and all the lights on at the same time. The contractor possibly used 220.32 for determining this service size. Table 220.32 shows a total reduction of total connected of 45% for 4 units. So if the units require 100-amp, 400-amp x 45% = 180-amp. 2/0 will handle this load per 310.15(B)(6).

wocolt

Member
Re: calculation for apartments

220.32 is correct for the optional calculation.
With the proviso that each dwelling unit has a single feeder and each unit has electric cooking equipment.
The method of load calculation under 220.32 is optional and applies only where one service or feeder supplies the entire load of a dwelling unit. If all the stated conditions prevail the optional calculations in 220/32 may bu used instead of those in Part II of Article 220.
The Exception says without electric cooking equipment in partII exceeds the computed load of partIII then the lesser of the two loads can be used.

Wm.Colt

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