Aluminum Wiring - is it Safe?

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I have aluminum wiring in my house. I was told that it's unsafe. Should I be worried?

Keep in mind that when we speak of aluminum wiring hazards, we are speaking primarily about branch circuit wiring – the wiring found in the walls of your home. There are many types of aluminum wiring still in use today. They are used primarily for service entrance (from your electric meter to your circuit breaker panel) and feeder conductors (i.e. from your main breaker panel to a sub panel). Aluminum service entrance and feeder wire is safe and legal and the most common way of wiring these devices, provided it is done properly.

For a short period of time (up until the 1980’s) aluminum branch circuit wiring was allowed in new residential construction by the National Electrical Code (NEC). Since that time, the practice has been outlawed by almost all state building codes due to the high incidence of fires caused from overloaded electrical circuits wired with aluminum wire. However, while currently banned for new construction, pre-existing aluminum wiring is still legal in homes containing it via a grandfathering clause in the NEC.

Should you be worried about it? That depends. When installed properly, aluminum wire is safe and will last for many years. The problems arose when this wire was installed on circuit breakers or fuses that were larger than the current-carrying capacity of the wire.

The problem has to do with the melting point of aluminum, which is lower than copper. For instance, a 12-gauge (#12) copper wire has a current limit of 20 amps, so it is safe to protect this wire with a 20 amp circuit breaker. A #12 aluminum wire, on the other hand, cannot safely carry 20 amps, so it must be protected by no bigger than a 15 amp circuit breaker. If this wire was installed on a 20 amp breaker, and the circuit was constantly drawing more than 15 amps, then the wire could melt, causing a fire. It should be noted that if this same scenario occurred using copper wire, while dangerous, it would be less susceptible to a fire due to melting because of the higher melting point of copper. That’s not to say that a copper wire would never melt; it can happen if it is not installed correctly.

Another problem with aluminum has to do with its high rate of oxidation. When replacing switches or receptacles connected to aluminum wire, you MUST use devices that are listed as suitable for use with aluminum wire. This sometimes noted as Al or Cu/Al on the device itself. These devices are usually harder to find and more expensive than their copper-wire-only counterparts. Another concern is extension or repair of aluminum wiring. If you add additional wiring in your home you must remember to never connect copper wiring directly to aluminum wiring. The metals will react with each other and cause potentially serious problems over time. You can only connect these types of wire together with a connector approved for such a purpose, such as a lug connector with separate openings for each wire, or a purple wire nut connector.

Lastly, if connectors and terminals securing aluminum wiring are not tightened enough (‘torqued’ properly), then these connectors can loosen over time, as the wire heats and cools during normal loading. These now-loose connections can allow arcing and pitting, eventually causing the circuit to fail. Connections should be checked for tightness in the circuit breaker panel, and on all switches, receptacles, and other devices at least every ten years.

If you’re at all unsure about the type of wiring in your home and whether or not it’s installed safely, call a licensed electrician to evaluate it. He or she can make recommendations for any repairs that may be necessary. It is a small price to pay to ensure the safety of your home’s electrical system.

Wurtsboro Electric Service, Inc.

Licensed electricians serving Orange county, Sullivan county, and Ulster county in New York

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