More Power to Ya
Submitted by: Michael Del Greco, New Jersey Home Inspector Lic GI 0121, President of Accurate Inspections, Inc, a New Jersey home inspection company
Todays homes need considerably more power than homes did just a few years ago.
We barely had hand-held hairdryers two decades ago. Numerous electrical services are obsolete.
In addition to the frustration of not having enough power, overloads on the electrical
service present a serious fire hazard.
To figure out how much current a home needs, you have to know the size of the
electrical service and the wattage of the equipment present. Knowing how a single-
phase service delivers the current to 120- and 240-volt circuits is also helpful. (Single
phase is the typical residential service.)
There are two 120-volt poles, which are the parts of the panel box that receive power
from the utility company. To energize a 120-volt branch circuit, you only use one of
these poles. As you add 120-volt circuits, you alternate with the right and left poles.
The 240-volt circuits use both 120-volt poles to service large appliances like a clothes
dryer, water heater, range/oven, and central air conditioner.
The following is a rule of thumb to help determine the service requirements for a
house:
1) Figure out the square footage of the living area.
2) Multiply the square footage of the living area by three watts for the lighting and
small appliance loads.
3) Calculate the total wattage used by the major electric appliances (e.g., dryer,
range/oven, water heater, central air conditioner, and electric heat). Figure the first
10,000 watts at 100% and the remaining wattage at 40%.
4) Add these figures together and divide by 240. The answer should reflect your
necessary amperage or service size.
If your maximum usage is close to or above the rated amperage of the service, you
should consult a licensed electrician for your best options.
Here is an example of a typical house situation that you can use as a reference:
120-Volt Circuits 240-Volt Circuits
(Load is shared by two poles) (Load is drawn off both poles)
Lighting & Small Appliance Wattage at 120 Volts
Actual Lighting 1,500
Toaster 1,000
Hair Dryer 1,500
Refrigerator 400
Microwave 800
Coffee Maker 800
Iron 1,000
Dishwasher 1,500
Washing Machine 600
Garbage Disposal 1,500
Approx.Sub Total 9,600
Major Appliance Wattage at 240 Volts
Range/Oven (all elements) 15,000
Water Heater 4,500
Dryer 4,800
Heat Pump 5,000
Heat Pump Back-up 15,000
Approx. Total for Major Appliances 44,300
The 9,600 watts distributed to both 120-Volt poles converts this figure to 4,800 watts
at 240 volts.
240-Volt Major Appliances -44,300
120-Volt Appliances (converted) - 4,800
Total wattage =49,100
The first 10,000 watts at 100% =10,000
Balance at 40% demand (39,100 x 40%) =15,640
Net wattage necessary =25,640
25,640 divided by 240 = 106.84 amps.
The service size should accommodate 107 amps. This means you would need a 125-amp service. The 150-amp service is a more likely choice and somewhat standard size.
Visions of the numbers listed above may have brought about bad memories from Jr.
High math class, but figuring out your amperage is an interesting task and really not
difficult.
Information provided by Michael Del Greco, New Jersey Home Inspector Lic. GI 0121, American Society of Home Inspectors Member 102273, Pesident of Accurate Inspections, Inc. A West Paterson New Jersey Home Inspection firm.
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