Any kind of electrical circuits, that includes electrical wirings at your home, need to be protected by certain overcurrent protection device. Current will be the amperage amount which is flowing through the wire or circuit.
Every circuit or wire has certain specified maximum current rating. In case, this current will be exceeded, the overcurrent protection device will shut off power to circuit, to prevent fire and any other serious hazards.
Nowadays, in most of the homes, the overcurrent protection device used for all circuits will be circuit breaker. However, in older homes having old electrical systems, this overcurrent protection device was usually a fuse.
Standard lighting or outlet circuits usually have screw-in fuses. In case of high-voltage circuits, e.g. those for electric dryers and ranges will be protected by a cartridge fuse.
How they work
Any fuse and cartridge fuses, will be “weak link” in the electrical circuit. There is metal strip inside the fuse which is connected to metal ends of the fuse body.
In case, there is short circuit or circuit fault anywhere, or if the circuit is overloaded, then metal strip, heats up and will quickly melt and open the circuit and shut off the power.
It is like light switch which turns off once only, then it should be replaced. While replacing cartridge fuse, new fuse should be of same type as old one and must be of same amperage and also voltage ratings.
This will be critical for safety because improper fuse may pose serious shock hazard or fire.
Cartridge fuses can be in cylindrical shape and will have contact points from both the ends. They will be rated for circuits for over 30 amps, 240 volts. Following are two basic cartridge fuse types:
- Ferrule-type fuses
They are mostly rated for 60 amps and have cylindrical metal cap from each end and appear like bigger version of fuses that you find inside plug end of the holiday lights.
- Knife-blade cartridge fuse
It is big brother to ferrule-type but has on each end flat metal blade. Knife-blade fuses can be used for protecting circuits more than 60 amps to 600 amps rating.
Where you can find them
All older electrical systems having fuse boxes have 2 or more number of fuse blocks and each contains 2 cartridge fuses. The main fuse will be one of this fuse blocks which is overcurrent protection device for your entire fuse box.
You can also find details of such cartridge fuse from National Stock Number search too. Besides that, there are other blocks available for any large electric appliances like:
- Electric water heaters
- Baseboard heaters
- Air conditioners
For accessing the fuse inside the block, you must carefully pull the wire handle or bail of fuse block. You can use your one hand for pulling out the block so that there is no chance of any electrocution in case something goes wrong.
Just remove the block completely from the box and for removing fuse from the block, use fuse puller, which is a pliers-like tool of plastic or some other nonconductive material meant for safety.