Wire Systems Old and New

A main difference between old electrical systems and new ones is the presence of a grounding conductor in contemporary wiring. Modern cable contains all three wires—hot, neutral, and ground—wrapped in protective thermoplastic insulation. Your house might have cable running through it rather than the old knoband-tube or metal-wrapped BX cable systems, but this is no guarantee that it’s got a grounding conductor. Cable installed in the 1950s only contained a hot wire and a neutral wire. The only way you’ll know for sure with your own cable is to check your electrical panel. You’ve already read that old wiring isn’t necessarily bad wiring, with the (sometimes) exception of BX cable, which can become damaged and be conducive to short circuits. The abuse usually occurs later as it gets hacked into. Replacing an entire system is expensive. New services installed in older homes usually incorporate some of the existing wiring into the new panel (unless it’s judged to be too corroded or unsafe). You and your electrician need to decide …

• If you can add any loads to your existing system.
• The compatibility of your current wiring with a new service panel.
• Whether your system is safe given its current usage.
• The practicality of completely rewiring your house.
• The cost versus the benefits.