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electrifier, Master Electrician
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CALCULATING THE SERVICE AMPERAGE Example 1 Imagine that

Resolved Question:

CALCULATING THE
SERVICE AMPERAGE

Example 1: Imagine that you’re working in a one-family
dwelling that has a floor area of 1,800 square feet (exclusive
of an unfinished cellar that’s not adaptable for future use, an
unfinished attic, and open porches). The appliances in the
home are an 11 kW range and a 6 kW, 240 V dryer.

1. What would be the general lighting load for
this home?

2.What is the minimum number of 120-volt, 2-wire branch circuits that would be required for this home?





3. What is the total net load (in VA) for the home?
Answer to Question 3: ____________________________________
Show all calculations to determine the total net load (in VA)
for the home in Example 1:
General Lighting and Receptacle Load: ____________________
Small-Appliance Branch Circuits: _________________________
Laundry Branch Circuit: __________________________________
Demand Factor Adjustments and Calculations: ____________
____________________________________________________________
Total General Lighting and Receptacle Load: _______________
____________________________________________________________
Range Load: ____________ Clothes Dryer Load: ____________
Total Volt-Ampere Demand Load Calculations: _____________
____________________________________________________________
Minimum Amperes: ___________


4. What is the total load service (in amps) for this home?---------------------------------------------------------





Example 2: Suppose you’re working in a one-family
dwelling that’s supplied with a 120/240 V service. The
home is also equipped with a 240-volt heat pump rated at
25 amps. The size of the home is 2,200 square feet (exclusive
of an unfinished cellar that’s not adaptable for future use, an
unfinished attic, and open porches). The home has a 10 kW
range, a 5 kW water heater, a 1.5 kW dishwasher, a 1.3 kW
compactor, and 18 kW of electric baseboard heat.

1.What would be the kVA for the heat pump?

2. What would be the general lighting load for this home?

3. What would be the total load service (in amps) for service for this home?
General Lighting and Receptacle Load: ____________________
Small-Appliance Branch Circuits: _________________________
Laundry Branch Circuit: __________________________________
Demand Factor Adjustments and Calculations: ____________
____________________________________________________________
Total General Lighting and Receptacle Load: _______________
____________________________________________________________
Range Load: ______________ Water Heater Load: ___________
Compactor Load: ___________ Dishwasher Load: ___________
Baseboard Heat: ____________ Heat Pump: ________________
Total Volt-Ampere Demand Load Calculations: _____________
____________________________________________________________
Minimum Amperes: ______
Submitted: 6 years ago.
Category: Electrical
Expert:  electrifier replied 6 years ago.
Chat Conversation Started
electrifier :

General lighting load is 3 watts per square foot. For 2 wire branch circuits we need to use the lighting load and add the 2 small appliance circuits, the laundry, the bathroom. 3 circuits are required for the lighting load since 3 watts X 1800 = 5400 and this equals 3 15 amp circuits at 1800 watts each. The minimum total circuits required is therefore 7 circuits.

electrifier :

I'll work at #3 now for you. This will take longer.

electrifier :

Small Appliance circuits 2 @ 2400 va laundry 1 @ 2400 bathroom 1 @ 2400 general lighting 5400 totals 15,000 va

electrifier :

Range at 11 kw is calculated at 8 kw and the dryer at nameplate or 6.4 kw.

electrifier :

Your example does not include a bathroom but one is required by code. This confuses the issue here.

electrifier :

The 15,000 va is adjusted using 3000 va at 100% and the remaining 12,000 va at 35% or 4200 va. We therefore have 7200 va in general lighting and receptacle loads. Add to this the 8,000 for the range and 6,400 for the dryer and we have 21,600 va when divided by 240 volts gives us 90 amperes. This would require at least a 100 amp service.

electrifier :

For example #2 the heat pump of 25 amps would be equal to 6000 va or 6 kva. General lighting load is 2200 X 3 = 6600 va.

electrifier :

Lighting load 6600 va, small appliance load 4800 va, laundry 2400, bathroom 2400 totals 16,200 va

electrifier :

3000 at 100% and 13,200 at 35% totals 7620 va.

electrifier :

There are only 3 appliances, not 4, that would be considered when looking to apply the 75% factor to additional applainces so that will not apply. They will be taken at 100%

electrifier :

Range again is taken at 8 kva, water heater at 5 kva, dishwasher, compactor at 1.5 kva and 1.3 kva respectively. Baseboard heat of 18 kva is taken at 100% as well. This will give us a total load of 47,420 va. including the heat pump. If this was air conditioning instead of a heat pump it would not be used at the same time as the baseboard heating so only the larger would be considered.

electrifier :

47,420 va = 197.58 amperes or a 200 amp service.

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