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Fuses Versus Circuit Breakers

technical-drawing-s

Circuit breaker electrical panels are installed in almost all new home construction. They have become the norm as people find them more convenient, but fuses are still a viable source of protection if used correctly. In most industrial installations, fuses are the preferred method of protection over breakers.

The primary advantage of a circuit breaker is that it can be reset. That really matters when you’re running small electrical circuits, like in your kitchen. Older homes really weren’t designed with such heavy electrical power draws such as microwaves, dishwashers and the many other modern conveniences we have today. Which is why the 2002 National Electric Code (or NEC) calls for two 20 amp general appliance circuits, plus dedicated circuits for refrigerators, dishwashers, food disposals and the like in new, or remodeled home kitchens. That’s a minimum.
A lot of older homes, started out with few circuits but over the years more are usually added.

With fewer circuits and ever increasing electrical requirements, fuses would be at great disadvantage, because you’d blow them periodically. But for bigger power levels, say above 40 amps, the advantages become less clear, particularly when the house electrical system has been properly designed for the expected.

Fuses are more reliable than circuit breakers. When a fuse rated at 20 amps exceeds twenty amps, it blows. Period. So if you buy a house with a fuses, don’t panic and decide you need circuit breakers right away. Even an old fuse will not betray you. Provided it’s not too big for the wire it protects, (and people are notorious for upsizing screw-in fuses when they have one blow) a fuse is a very effective way of protecting the circuit, the appliance and people.

A fuse is nothing more than a wire that melts when a known level of current flows through it. Fuses don’t age. But if you need more circuits you’ll need to put in a new breaker panel or subpanel as nobody makes fuse boxes for residential applications these days.
Remember the purpose of a fuse is to prevent circuit from overheating and starting a fire.

Both fuses and circuit breakers are overcurrent protection devices as defined by the NEC. You chose your breaker or fuse size after you’ve picked your wire size. Of if you’ve picked a fuse size, then the wire must match it.

Older breakers can ‘freeze’ in place. Breakers need to be exercised, turned on and off, so corrosion doesn’t weld the contacts together enough to make the breaker slow, or reluctant to blow. Old “Pushamatic” panels are notorious for this problem. A good practice when you have breakers is to flip all your breakers on and off once or twice a year to prevent the breakers for such seizures.

Fuses are fast. They open in one fifth of a cycle, breakers 1.5 cycles. That’s not much time at 60Hz, but it matters when you’re trying to protect computer equipment. A fuse might make the difference if you get hit with lightning.

Fuses are more flexible. You can get them with a dual element time delay which allow for a temporary overload in amps which occurs when AC compressors, fridges, dryers or other appliances which have high start up current draws. In a dead short situation these fuses will blow in a fifth of a cycle.

Of course, fuses must be changed, while breakers need to be reset. To change a fuse, turn the circuit to off and use an insulated tool, like linesman’s pliers o pull the fuse, and push in the new one. Screw-in fuses (type H) can be safely unscrewed if you resist the temptation to stick your finger in the socket. And remember to put exactly the same rating fuses back in. Remember an up rated fuse does NOT up rate the wire behind it.

But breakers sometimes have to be changed too. Square D, a manufacturer renowned for quality, only warrants its breakers for one trip. The reason is that every trip involves an electrical arc, and potential damage to the breaker’s contacts. A breaker that trips often should be changed. Fuses are generally cheaper, but at the household current level, good breakers are quite affordable.