Understanding Fuses in Older Homes

The electrical circuits of older homes that haven’t yet been updated are protected and controlled by fuses located in a central fuse box. Like circuit breakers, they protect against circuit overloads and short circuits. However, these fuses “trip,” you don’t reset them. Instead you must replace them when they blow (meaning, when they burn out).

What are fuse controls?

There are two different types of fuse controls: the 120-volt circuit and the 240-volt circuits, the latter being those found in older homes. For these 240-volt circuits (which control major appliances), the fuses are small cartridge-like devices that fit between metal contacts, usually fitted into a fuse block that can be pulled out from the fuse panel in order to change the fuses. Like circuit breakers, fuses are sized to match the gauge of the circuit wires, preventing circuit wires from drawing more power than they can handle, so using the correct fuse size is vital for safety purposes. Never replace a burned-out fuse with one of larger amperage rating. In fact, there’s a new type of fuse (an Edison-base) that has a specially shaped base which prevents the wrong-sized fuse from ever being inserted into the socket.

What causes a fuse to blow?

There are two conditions that can cause a fuse to blow: when too many lights or plug-in appliances draw power from the circuit and when a hot wire somewhere in the system touches either the grounding pathway or a neutral wire (aka, a short circuit).

The first condition overloads the capacity of the fuse, which causes the internal metal of the fuse to melt. This then causes all lights, outlets, and appliances powered by that circuit to go dead. To fix the problem short-term, you can replace the fuse with one of the same size, but to fix the problem long term, you’ll need to move some plug-in appliances to other circuits. Appliances that heat up or that have motors are major culprits of overloads since they draw such a large amount of power.

The next condition – the short circuit – is usually the result of wire problems, whether loose wire damaged wires, or a wiring problem within the appliance itself. Often times, just replacing the fuse won’t do much good. Usually will just lead to the new fuse blowing out out as well, unless of course the short circuit itself has been fixed somehow.

How do I fix a blown fuse?

Begin to solve the problem by unplugging every lamp and appliance and replacing the burned-out fuse. If the new fuse works, then the problem was clearly in one of the appliances or lamps. But if it persists, then the problem lies within the actual circuit wiring. If this is the case, while you can visually inspect the circuits yourself, it may be necessary to hire a professional electrician to actually fix the issue at hand.