Parallel and Series Circuits
Electric circuits can be connected as either parallel or series. The power source or the load can be set up as
parallel or series. Any circuit can be a mixture of parallel and series, both on the load end and the power supply
end.
Series: In a series circuit, the electricity must travel through each of the parts of the circuit, one at a time.
1. This is a single battery with 3 bulbs wired in series. A series
circuit will make the bulbs dimmer each time a new bulb is
added, because the filament in each bulb has a high amount of
resistance and the voltage gets lower with each bulb. If one
bulb burns out in a series circuit, all the bulbs quit working. Most
houses do not use series wiring, although holiday lights often use series circuits.
2. These are 2 batteries wired in series with 1 bulb. The voltage of each battery is
1.5 V. The voltage increases as the current goes through each battery, the total
voltage is 3 V.
Series battery arrangements are often used in flashlights. Car batteries use 6, 2V
cells, connected in series to get 12 V.
Parallel: In a parallel circuit, there is more than 1 pathway the electricity can follow.
3. This is a single battery with 3 bulbs, wired parallel. House
wiring is done this way. Each bulb has its own pathway back to
the power source. The other bulbs stay on when 1 of the bulbs
burns out. The bulbs do not become dimmer when more bulbs
are added. Because the electrons can go 3 different pathways,
the amount of Amps in any of the 3 circuits is 1/3 of the total
Amps.
4. This shows 2 batteries wired parallel with 1 bulb. The Volts will be the same as
with 1 battery, but there will be 2 times as many Amps because each battery is
producing its own amount of electrons.
This is a mixture of series and parallel circuits:
Electrical Safety
Fuses: a fuse is a conductor which is designed to fail if too much electricity (Amps) goes through it. When the
fuse burns up, the circuit turns off. The fuse is always wired in series with the objects the fuse is supposed to
protect. The objects or appliances are wired parallel to each other, after the fuse.
Fuses are used for heat protection, the fuse burns up before the other parts of the circuit are damaged.
Fuses are rated in Amps. If new electrical appliances are added in parallel to a circuit, each device increases the
amount of electricity flowing through the circuit by the amount of Amps the device uses. If the Amps used is
more than the rating of the fuse, the fuse burns up.
In this drawing the fuse is rated at 10 A. The light bulb only uses 7.5 A, so there is
not enough current to make the fuse burn up.
If another light bulb with 7.5 A is added in parallel to the existing
circuit, the total amount of Amps is 15. Because the fuse is rated at
10 A, the fuse will burn up when 15 A of electricity runs through it.
Circuit Breakers: Most houses are protected with circuit breakers. The circuit
breaker has metal which bends when it gets hot instead of burning up. Circuit breakers
have an advantage over fuses; the circuit breaker can be reset when it cools down. The
fuse cannot be reset and has to be replaced.
Each breaker is wired parallel to all the other breakers in the house. A typical light or
wall outlet circuit will be 20 A. An electric baseboard heater will be 30 A. An electric
dyer or electric stove will be 50 A. There is usually one main breaker which is wired
in series to all the smaller breakers.