Overloading Electrical Circuits
Electricity has enriched our lives. Despite the many benefits,
electricity can also bring danger -- the most common being house
fires. It is estimated that over 40,000 residential fires are caused
by electrical systems every year in the United States. Causes
include arc faults, short circuits, or overloading of electrical
circuits. This article discusses overloading electrical circuits.
First, we must understand some
basics about typical home electrical systems. The electrical service
enters the house and connects to a main electrical panel. From the
main electrical panel, wires run in different directions throughout
the house to power lights, outlets, ceiling fans, air conditioners,
and various other direct-wired electrical appliances. These
wire-runs are called branch circuits.
In home construction today,
the typical branch circuit consists of three wires -- the hot,
neutral and ground wires. When a light or electrical appliance is
turned on, electricity begins to flow in the hot and neutral wires
of the branch circuit to which that light or electrical appliance is
When electricity flows through
a wire, the wire heats up because of its resistance to the flow of
electrical current. Both the size of the wire (resistance increases
as the wire diameter gets smaller) and how many electrical devices
on the circuit are drawing electricity (more devices increase the
electrical current) affect the amount of heat generated in the wire.
To keep the wire from getting too hot and starting a fire, the
designer of the branch circuit wiring does two things:
- Attempts to size the
wire large enough to handle the estimated electrical load on
- Attempts to contain the
amount of electrical load on the branch circuit by limiting
the number of potential electrical appliances that can be
running at the same time on that circuit (i.e. places only so
many outlets on one branch circuit or puts larger pieces of
electrical equipment on circuits dedicated to that equipment
electrical codes help with the design assumptions, how the homeowner
will use the outlets in the house is just a guess. The homeowner can
plug in and run too many appliances on the same circuit at one time
and overload the circuit.
This is why electrical fuses and circuit breakers are used in the
main electrical panel. Their function is to sense the overloading of
circuits (and short circuits) and shut off power to that branch
circuit before the wires get too hot and start a fire.
However, circuit breakers can malfunction and fail to trip.
Homeowners can try to fix a "nuisance" fuse by placing a larger fuse
in the electrical panel that allows more electrical current to flow
in the branch circuit than what it was designed for. Homeowners can
also use plug adaptors and extension cords to plug in too many
electrical appliances into one electrical outlet.
What Can the Homeowner
Most home circuits are
designed as 15-amp branch circuits. A hair dryer can draw 1400
watts, an iron 1000 watts, a portable heater 1200 watts, a vacuum
cleaner 600 watts, deep fat fryer 1300 watts, and a portable fan
There are no hard-and-fast
rules as to how often a home electrical system should be inspected.
Here are the recommendations from the NESF:
If your last inspection was:
- 40 or more years ago,
inspection is overdue.
- 10-40 years ago,
inspection is advisable, especially if substantial electrical
loads (high-wattage appliances, lights, and wall outlets or
extension cords) have been added.
- Less than 10 years ago,
inspection may not be needed, unless problems are noticed.
It may be difficult to
determine when the last electrical inspection was made. Look on the
inside of the door to the electrical panel. The electrician
performing the last inspection may have written the date there.3
As a homeowner, be aware of your electrical system. Look and listen
for problems. If you hear buzzing or crackling coming from outlets
or light switches, don't ignore it. If appliance or extension cords
are hot to the touch, you have potential problems. Contact a
qualified electrical professional to assess the problem and make the