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Inspecting Home Electricity (part 2)

This article is meant for reading and helping you understand some of the issues home inspectors look for when inspecting an electrical system of a property. I strongly recommend having a licensed professional evaluate your home’s electricity, if you are experiencing problems.

Both the fuse and the circuit breaker (CB) are intended to open a circuit for excessive current.

The traditional fuse is a circuit element that is a one time use element. That is, excessive current will cause it to open and to restore the circuit the fuse must be replaced with a like element. They are often cylindrical and come in holders for somewhat easy replacement but sometimes are soldered in place.  They usually use a fusing element that is metal with a low temperature melting point that literally melts under overcurrent conditions. The cylinder is often made of glass to allow inspection of the fuse element to see it it is blown.

There are some self-resetting fuses that will heal after a certain amount of time. These are called PTC fuses and have a high resistance state when hot. If the heat was caused by overcurrent then removing the overload will restore the fuse to operation mode.

A circuit breaker is a multiple use device. It is usually permanently installed in equipment. It generally has two mechanisms for breaking the current: a magnetic portion which opens with a large current and a thermal part that also opens under overcurrent...  the thermal part has a lag so these typically go slower than a fuse but with very high currents the magnetic part will open quickly. The circuit breaker usually has a button or handle to reset it after it has cooled down.

Circuit breakers are usually more costly and larger than fuses. Fuses are more likely to be abused because if blown and the user wants to return the equipment to operation AND there is not a spare fuse then he will substitute a fuse of higher value or short out the fuseholder in frustration and defeat the saftey of the fuse.

How many amps and volts do you need?

The more amps you have in a home, the more electrical devices you can have in use at any given time. The typical standard for modern usage is 100 amps; less than 100 amps may not be adequate for your needs. Large homes, and homes with central air-conditioning or electric heat will need more power, typically 150 to 200 amps. As an analogy, think of amps as a tunnel, twice as many cars can travel through a tunnel with two lanes than a tunnel with one lane.

Volts determines the types of electrically powered devices that can be used in a home. Lights, small power tools, small kitchen appliances, bathroom appliances, small room air-conditioners, etc. utilize 110 volt power. Electrically heated homes, electric ranges, large room air-conditioners, central air-conditioning, large power tools, clothes dryers, etc. utilize 220 volts. Going back to our analogy of tunnels, think of a small tunnel as one that is large enough to accommodate cars, think of a large tunnel as one that is large enough to accommodate trucks; that is, the small tunnel is analogous to 110 volts, and a large tunnel is analogous to 220 volts.

Every electrical service has some amps and some volts; the typical average home needs 100 amps and 110-220 volts. Now that we have talked about amps and volts, let’s not forget the electrical distribution within the home. The more circuits you have in a home, the less the chance that a circuit breaker will trip or that a fuse will blow. For example, an average size home with only seven circuits is much more likely to have overloaded circuits than the same home with fourteen circuits. Even if there are enough amps and volts in a home, it’s important to be able to adequately distribute the power throughout the home. Going back once more to tunnels, the more tunnels that are available to accommodate traffic, the less chance that a traffic jam will occur; similarly, the more circuits, the less chance that a circuit breaker will trip.

How many appliances can a particular circuit handle?

To determine how many watts a branch circuit can handle, you need to know two things. First, you need to know how many amperes, or amps, for which a circuit is rated. An amp is the amount of electrical current that flows through a circuit. In most homes, lighting and small appliance circuits are 15 or 20 amps, and major appliances are on 20, 50 or even 60 amp circuits.

Second, you need to know the volts flowing through the wires. Volts are a measure of the pressure that causes current to flow through a circuit. Generally, household wiring is 120 or 240 volts.

To determine the amount of wattage a branch circuit can handle, multiply the circuit's amperage by the circuit's volts. A 20-amp, 120-volt circuit can handle 2,400 watts.

The following list gives you the average wattage rating for common household equipment. For specific information on your home equipment, check the manufacturer's listing found in your owner's manual or on the information plate of the equipment. For lighting, check the wattage rating of the bulbs being used.

All wattages are approximate. See your equipment documentation for exact wattage.

Major Appliance

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