"Understanding Your Home" by Building Inspector Mark Visser
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Understanding Electricity
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Electricity is a mysterious subject to most people and yet basic understanding of house wiring is necessary to deal with emergencies.
Electricity flows through wires in an electrical circuit. 'Hot' wires (usually black) carry electricity to where it is needed. Once it has been used, the electricity travels back to its source along neutral (white) wires. Since the early 1960s electrical cables contain a third wire (usually uninsulated) called ground. This ground wire is a safety feature, providing a path for short circuits back to the fuse or circuit breaker.
Electrical power enters the house through wires running from the overhead street wires, or through an underground pipe called conduit.
Homes are supplied by two 120-volt 'hot' wires and one neutral wire. The two 120-volt wires can be combined to supply the 240 volts needed for major appliances.
The distribution panel, also known as breaker or fuse panel, controls the distribution of power throughout the house. The panel contains fuses or breakers that protect the circuits in the event of overloading or faults. 100-150 Amperes (amps) is considered a basic service for a modern house. Many older homes still have only a 60 amps service. 200 Amps is usually necessary if the house has electric heating or for larger homes.

Distribution panel
The main disconnect can be found in a separate box near the panel, or within the panel in the form of a large circuit breaker or fuse switch.
The circuits distribute the power throughout the house. Each cable running from the panel is an individual circuit. Each circuit must be protected by a fuse or circuit breaker of an appropriate maximum amperage. When exceeding this power rating by overloading, the circuit blows the fuse or trips the breaker.
120-Volt circuit are used for lighting and receptacles.
240-Volt circuits are used for major appliances. A circuit can be dedicated to just one outlet, such as a counter receptacle in the kitchen, or to one appliance such as the refrigerator.
Electrical terms. To make it easier to understand some electrical terms, we will compare them to the plumbing system.
VOLTS Plumbing - water pressure is measured in lbs/sq. inch
Electric - pressure is measured in VOLTS
AMPS Plumbing - supply is measured in gallons/minute
Electric - supply is measured in Amperes (AMPS)
Plumbing - amount of water depends on the size of the pipes
Electric - amount of electricity depends on the size of the wires
WATT A unit of electrical power, measured by multiplying AMPS and VOLTS

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