Electrical System
83
Series/parallel
Series/parallel circuits have some sections wired in
series and some in parallel. See Figure 7.31.
What can go wrong?
There are three types of failures that can occur in an electrical circuit:
1. Shorts
2. Opens
3. Increased resistance
Shorts
A short is when electricity takes a path that it was not designed to take bypassing a component in the circuit.
A common example of a short is a wire with insulation that chafed through, exposing the copper conductor. The
bare copper will short the circuit when it touches a ground source.
Opens
An open is when current can not complete its path back to the power source. A common example of this is a
burned-out lamp (light bulb) in a series circuit.
Increased resistance
Increased resistance is, as the name implies, an increase in resistance.
Arguably the most common electrical failure, and the hardest to find, increased resistance can have more subtle
symptoms than outright open circuits. Many times affected circuits will still partially function. It is not an open because
there is some current that can get through, but the increase in resistance is enough to affect the circuit.
This can be caused by loose or corroded connections, or connections that are insulated by grease, paint, or coat-
ings. Fasteners finished in oil/phosphate or black oxide are bad conductors. Use bright fasteners (zinc coated).
Resistance can be a problem on the ground side as well as the hot side of a system. Remember that electricity
must complete a loop (circuit) back to the battery post. Any resistance in that loop will interfere with the flow.
Figure 7.31
Battery
Lamp Switch
Lamp
Lamp
Lamp
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