How long does house wiring last?

House wiring does not come with an expiry date. It is judged by its type and its condition, and the parts that usually give out first are the insulation around the conductors and the connections at each outlet, switch and splice. How long a house's wiring stays safe depends on what kind it is, how hard it has been worked, and how much heat it has lived with.

It depends on the type

Knob-and-tube (before 1930). Knob-and-tube wiring dates from before 1930, so any that remains is among the oldest wiring still in use. It also limits what you can do around it: it can be a fire hazard when in contact with insulation.^[6]

Aluminum branch circuits (about 1965 to the mid-1970s). Homes built before 1965 are unlikely to have aluminum branch circuit wiring, but cable installed between 1965 and the mid-1970s may.^[1] Here the weak point is the connections. According to CPSC, several deterioration processes in aluminum wire connections raise their resistance to current, and the damage is cumulative.^[1] That added resistance makes the connection overheat, sometimes to hazardous levels, whenever current flows.^[1] Worse, failing aluminum connections seldom give easily detected warning signs.^[1] CPSC's permanent fixes are complete replacement with copper, or repairing every aluminum connection with a method CPSC recommends.^[1]

Plastic-sheathed cable (later decades). Most later houses use plastic-sheathed cable. When it fails, the cause is often something that has happened to it since it went in: a loose connection, an overloaded circuit, damage during a remodel, or an amateur addition.

What shortens wiring's life

Heat and overloading. Too much current makes wires hot.^[2] A March 2008 U.S. Fire Administration report warned that many older homes have outdated wiring that is deteriorating, inappropriately amended, or insufficient for the electrical loads of a typical 21st-century household,^[7] and that overloading will heat up wiring that already could be deteriorating, crumbling and no longer a good insulator.^[7] Cords and appliances crammed onto one circuit, all add heat, and the wrong size fuse can let too much current flow and overheat the wiring.^[2]

Insulation packed around old wiring. Knob-and-tube can be a fire hazard when in contact with insulation,^[6] so if you plan to insulate an older house, have the wiring checked first.

Loose connections. A loose screw holding a wire or a worn-out switch can lead to arcing, overheating or a fire.^[2]

Keeping an eye on your wiring

Looking after wiring, for a homeowner, is mostly watching for warning signs and calling an electrician early. None of it involves opening anything up.

• Do a regular walk-through. CPSC staff recommend inspecting the electrical products in your home every six months,^[2] looking at cords, outlets and switches for anything warm, loose, damaged or overloaded.
• Treat warmth as a warning. Unusually warm outlets or switches may mean a loose connection that can start a fire.^[2] Stop using one that feels warm until an electrician has checked it.
• Have the protective devices checked. CPSC says GFCIs can fail without showing any sign of failure and that AFCIs can stop working without showing one either,^[2] so ask the electrician to check them whenever they are working in the house.
• Stop living on extension cords. "Extension cords are not as safe as permanent house wiring."^[2] If a cord is in permanent use, have new outlets installed where they are needed.^[2]

When to have it checked

Have a licensed electrician evaluate the system when you buy a house, before a remodel or a large new load such as an EV charger or heat pump, before insulating walls or an attic in an older house, and whenever you see signs a house needs rewiring. A home inspection helps at purchase: under Virginia's rules a home inspection report covers the electrical system's readily accessible parts, including the conductors, and its list includes solid-conductor aluminum branch circuit wiring unless the inspection contract limits it.^[5] It cannot see inside closed walls, so an electrician's assessment is the follow-up when there is any doubt.

When to call a licensed pro

Call an electrician promptly for a burning smell, scorch marks, hot outlet or switch plates, flickering in several rooms, or circuits that have stopped working. Repairs, new circuits and rewiring are electrician's work, and in Virginia no individual may work as a tradesman unless licensed.^[4] New circuits and rewiring also need a permit, because a permit is required before work starts on electric wiring;^[3] like-for-like replacement of switches, dimmers, standard 15- or 20-amp 125-volt receptacles, light fixtures and ceiling fans in a house is an ordinary repair that needs no permit.^[3] You can check an electrician's licence on DPOR's record.

If the verdict is a rewire, see what rewiring an old house involves and what it costs in Virginia. Buying a house with old wiring? Read whether knob-and-tube is a problem when buying in Virginia.

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