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More Power to Ya

By: New Jersey Home Inspector Michael Del Greco
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


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

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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