Fuses and Circuit Breakers Inspection – Ensuring Operational Integrity
Circuit breakers are more convenient than fuses because once they have been tripped, they can be reset like a switch, but if a fuse has blown, it must be replaced. Circuit breakers, however, are somewhat less reliable than fuses, as they have been known to “freeze” in the on position and require manual tripping periodically to ensure operational integrity.
There have been many reports questioning the safety of the Federal Pacific Electric (FPE) service panel box and its Slab Lok circuit breakers. Some of the breakers have reportedly failed to shut off (trip), in response to an overload and arcing has occurred in the panel box. It is recommended to replace the panel box as a safety measure.
The capacity of a fuse must be matched with the current-carrying capacity of a branch circuit, and when a fuse has been blown, it must be replaced by a new fuse with the same current-carrying capacity. Too often, however, homeowners replace a 15-amp fuse with a 20- or 30-amp one, without realizing that all three are physically but not electrically interchangeable. In this case, if there is an overload on that branch circuit, the fuse will not blow, but the wires will become excessively hot and could cause a fire. This problem can be corrected by replacing the fuse with a Fustat – basically a fuse with an adapter that fits into the fuse holder in the panel box. Once the adapter is inserted, it generally cannot be removed. These adapters are sized so that they accept only fuses of a specific current capacity, and are not interchangeable.
Some fuses act like circuit breakers. Cooper-Bussmann, for instance, manufactures 15- and 20-amp mini-circuit breaker plug fuses that fit into any standard fuse socket. The mini-breakers have a small push button that pops out when the circuit is overloaded. To reset the circuit breaker/fuse all you have to do is push the button back in. In addition, the mini-breakers are also designed for time delay to handle temporary starting loads so they don’t trip unnecessarily when motors or appliances start up.
Nowadays, most newer homes have a circuit breaker panel, while many older homes may still have the old fuse panels. Either way, fuses and circuit breakers have the same job of protecting branch circuits from sustained short circuits and overloading. The most common circuit breaker and fuse sizes are 15 amp, 20 amp, 30 amp and 40 amp. Generally, the circuits which supply lights and receptacles in your home are protected by 15 amp or 20 amp fuses/circuit breakers, while your stove or range will likely be protected by a 40 amp breaker.
Older homes generally have a multitude of outlets, all running off of one circuit, which results in frequently blown fuses or tripped circuit breakers. Many people believe that if they install a larger fuse or circuit breaker their problems will be solved, but this creates a dangerous overload on the branch circuit wiring. Cables and conductors are rated by how many amps they can safely carry continuously, for instance a #14 cable is rated at 15 amps and a #12 cable is rated a 20 amps. If you put in a 30 amp fuse or circuit breaker you will exceed the safe limits of the cable.
If a cable carries more current than it is rated for, it may cause a dangerous situation. Large cables with less resistance can carry more current than smaller cables, which have more resistance. When a circuit is overloaded the conductors will start to produce a heat which can melt the insulation covering and result in an electrical fire. Instead of installing larger fuses and circuit breakers, reduce the number of outlets on overloaded circuits.