PAUL HAY Capital Projects
Topic: Calculating Electrical Load
Author: Paul Hay
e-mail: paul.hay@phcjam.com
profile: www.linkedin.com/in/phcjam
Electricity - Calculating Service Amps
Example 8.1: Calculate (A) the service current required for a 200 m2 residence, with appliance loads stated below; (B) main breaker size, and (C) size of service entrance conductor.
BRANCH CIRCUIT REQUIREMENT/SPEC POWER (W)
1. Lighting and General Use Circuits: Area of house x 30W = 6,000
2. Small Appliances Circuits:
a. Kitchen 2 x 1,500W = 3,000
b. Laundry 1 x 1,500W = 1,500
c. Additional circuits 0 x 1,500W = 0
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Subtotal = 4,500
3. Dedicated Circuits:
a. Cooking Range 1 x 8,000W = 8,000
b. Water Heater 1 x 5,000W = 5,000
c. Microwave Oven 1 x 1,200W = 1,200
d. Refrigerator 1 x 600W = 600
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Subtotal = 14,800
4. General Load: Sum of items 1 thro= 3 25,300
5. Derated Load: 10,000 + [0.4 x (General Load - 10,000)] = 16,120
6. Heating and Cooling: A/C @ 10,000W 10,000
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7. Total Electrical Load: Derated Load + Cooling = 26,120
8. Service Current: Total Electrical Load ) Service Voltage (220V) = 118.73A
9. Min. Allowable Conductor Current: 1.5 x Service Current = 178.1A
10. Breaker Amperage: 0.8 x Conductor Rating = 142.5A
NB. The nearest breaker available is 150A. Therefore, minimum copper service conductor should be #1 AWG.
FURTHER READING
JLC Field Guide to Residential Construction: A Manual of Best Practices, Vol. 2, Manley Wood LLC, USA, 2006
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