Doin' the circuit:
A few shocking facts about home wiring
by Roger Faris
Two recent experiences with residential electrical panels reminded me of the importance of accurate labeling of the circuit breakers. In the first, I was helping my brother-in-law install a 50 amp double-pole breaker for a sub-panel in his new workshop. To make space in the main service panel, we carefully removed the double breaker that had once provided power for a hot water heater. The old tank had been replaced with a gas fired heater. As we began to remove the old wire we became aware of an error. The circuit breaker had been mislabeled. We had cut the power to a bathroom heater.
The second experience was at a neighbor's house where I was trying to help find the cause of a dead circuit which served the kitchen area. The neighbor had been getting by with several extension cords, but that was not a safe or convenient remedy. Using a volt tester, we checked the breaker that was supposed to be providing the power. It was fine, so we began to trace the wires, hoping to quickly locate a loose connection or damaged outlet. The search grew to include exploring a dusty attic and an unpleasant crawlspace under the house. We eventually realized that we'd been following the wrong circuit. Returning to the source, we found that the breaker which needed resetting was labeled "spare".
A good map of the electrical circuits can make solving problems much easier, and it can greatly reduce the hazards of working with electricity. When everything is working properly, it's easy to create a list of which fuses or circuit breakers control each light, outlet, or appliance. This is done by simply shutting off one circuit at a time and exploring thoroughly to discover what is no longer working.
This first step in becoming familiar with your home wiring system may lead more questions. To fully understand how power flows through your electrical system you might want to take a class, or read a good book. If you live in an older home, Wiring Simplified, by H. P. Richter, is very useful. If all of your wiring is more modern, the Step By Step Guidebook to Home Wiring shows how each type of circuit works. Both books are inexpensive paperbacks and are often available at electrical supply stores.
There are other ways to become familiar with electrical systems. The first biography I read as a boy described the life of Thomas A. Edison. The idea of performing experiments with high voltage current was appealing. I could imagine myself engaging a series of enormous knife switches, creating flashes of intense blue light. Years later my wishes were fulfilled, and my electrical education really began.
It was in 1975 that some friends and I decided to purchase a 122' retired military ship. It was too old, large and impractical to have much value, so we were able to buy it for $6,000. For the next several years it was our home, and the source of many adventures. The vessel had a main engine weighing 80,000 pounds, a powerful auxiliary engine, and a remarkable electrical system. Huge 110 and 220 volt generators produced power to operate pumps, winches, and other equipment. One electrical panel included switches labeled "gun heater". It is probably just as well that the guns had been removed.
The previous owner had mentioned that the electrical system could be hazardous. He had burned the soles of his feet when he made accidental contact with the 220 volt panel. The generator output was regulated by large rheostats. I discovered that a small adjustment error could cause all of the engine room lights to explode. We quickly learned to be careful, and gradually gained an understanding of the ship systems. We also learned about what to do when something fails to function. The ship was old. Solving problems was a daily activity.
Home wiring can present some of the same challenges that we faced. Our electrical equipment had been exposed to salty air. A house in Ballard is unlikely to experience an ocean wave crashing against the door, but an old electrical panel located on the back porch may still be damaged by our marine climate. The fuse holders turn green and electrical connections deteriorate. This is one reason why new equipment must now be located inside the house.
Modern residential electrical systems have many advantages. The newer service panels have a single main disconnect switch which allows all power to be quickly turned off. Some older houses have fuse boxes which have been "hot-wired", sending power to additional sub-panels without first passing through the main fuses. This can allow the wires coming in from the electrical meter to be overloaded and damaged. It can also provide a shocking surprise to anyone who is working on a system which they thought had been shut off. I still have the remains of a screwdriver which melted during such an encounter.
Newer electrical systems usually have plenty of circuit breakers, each with the correct rating to protecting the wires in that circuit. Older electrical panels may not have enough circuits to meet modern demands. They often have too many electrical loads connected at the same time, causing fuses to burn out. If the replacement fuse is the wrong size, the wiring may not be adequately protected from overheating. This simple mistake can cause a house fire. A basic rule is that if a circuit has any 14 gauge wire, it must be protected with a 15 amp fuse or breaker. A circuit with 12 gauge wire is protected by a 20 amp fuse or breaker. A circuit serving a larger appliance, such as a 230 volt clothes dryer, may have 10 gauge wire, and be protected by two 30 amp fuses or breakers.
Modern wire has insulating materials which resists abrasion, moisture, and heat. Some older types of wire are less durable. The old knob and tube wiring is suspended in the air by ceramic knobs, and passes through the wood framing in ceramic tubes. Since it was not designed to be buried under a thick layer of attic insulation, it is now particularly important that this type of wiring be protected by a 15 amp fuse or breaker. An even better precaution is to further limit the load on these old circuits to 800 watts or less. Since this is less than half of the load which will cause a 15 amp fuse or breaker to trip, we need to carefully add up of what is connected to such a circuit. Lights, clocks, and radios are generally fine. Most space heaters demand too much power. The wattage should be clearly marked on each device. You may be wondering about the electrical load requirements for gun heaters. Sorry, I can only provide that to people with security clearance.
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