Originally Posted By: dvalley
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Here ya go…
Load Calculations
General Lighting
Take the square footage of the house times 3va (volt-amperes)= __________ then add that number to 4500, which would be 2 small appliances and 1 laundry load.
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Take this subtotal and determine the *total general lighting load & small appliance as follows:
Take the first 3000 at 100% 3000
Take the remainder at 35% _____
(Total general lighting load
and small appliance minus 3000)
Then add those two together to
obtain the *total general
lighting load & small appliance _____
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Now determine the following and add them to the *general lighting load & small appliance:
Dishwasher 1200 va
Disposal 1200 va
Dryer 5500 va
Oven 8000-12000
(On the oven check the breaker size. If it is a 40 amp breaker it is 8000. If it is a 50 amp breaker it is 12000.)
Air Conditioner 5500-12000
(On the air conditioner, 700 sq ft requires 1 ton of air conditioning. A house of 2800 sq ft would require 12000 va whereas a house of 700 sq ft would only require 5500 va.)
Swimming pool 1500
Hot Tub 9000
(On the hot tub if the breaker is a 50 amp it would require 9000. If it is a 30 amp, it would require 6000.)
Electric Heaters, well pumps, and compressors would be figured out by taking the breaker size times the voltage required to use the breaker, and then times 35%. ( A single pole 20 amp breaker would result in 840 va [120 x 20 x .35=840]. A 20 amp two pole would be 1680 va [240 x 20 x .35=1680].)
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Take the total of the above and divide it by 240 volts. The result will be the total amount of amperes needed by the house.
A house at 80 amperes or less is good for a 100 amp panel and service.
A house at 81 amperes to 90 amperes is marginal for 100 amp panel and service.
Anything over 90 amperes should be upgraded to at least a 150 amp panel and service.
A house at 160 amperes or less is good for a 200 amp panel and service.
A house at 161 amperes to 180 amperes is marginal for a 200 amp panel and service.
Anything over 180 amperes should be upgraded to a higher than 200 amp service and panel.
Here is an example of a load calculation:
The house is 2000 sq ft, therefore 2000 x 3va =6000
6000 + 4500= 10500
The 1st 3000 is at 100% 3000
The remainder of 7500 is at 35% 2625
The sum of these two is: 5625
This number is the general lighting load and small appliance.
The house has a disposal 1200
A dishwasher 1200
A electric dryer 5500
A electric oven at 50 amps 12000
A air conditioner 10000
The sum of all these appliances plus the general lighting load and small appliance is: 35525
Take 35525 and divide it by 240 volts = 148 amps
This house would require a panel and service upgrade to at least 200 amps.
--
David Valley
MAB Member
Massachusetts Certified Home Inspections
http://www.masscertified.com
"Some cause happiness wherever they go; others, whenever they go."