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2018 National Home Improvement Estimator, All Rights Reserved Page 409

Chapter 15, Electrical

Most older homes have electrical systems that are in perfectly good working order – but completely
inadequate by modern standards. They have too little power, too few circuits and far too few outlets.
Even if the electrical service in the home has been upgraded in the last 25 years, more circuits may be
needed to keep up with the demand created by today’s multitude of electrical conveniences.

Few homes built before World War I were wired for electricity. Circuits were added later, usually gouged
into plaster walls or run behind baseboards. In the 1920s and 1930s, most new homes were planned for
40 amps. The next jump was to four 15-amp circuits, or 60 amps total power. Many rooms had only a
single duplex receptacle and a switched light fixture. By the 1950s, 100 amps was considered adequate
power, unless the plan included an electric range or electric heat. Since the 1970s, 150 amps has been
considered the minimum for a small home and 200 amps a better choice for most homes.

Enough Power?
The primary electrical shortcoming in older homes is too little amperage. Your first task is to determine
how much power is available at the distribution panel (or fuse box). There are three ways to find out:

•The first limitation is the current-carrying capacity of the service entrance wire. The wire gauge may be
marked on the insulation where the wire enters the weatherhead or where the cable emerges from
underground conduit. If there’s no marking, an electrician can measure the wire gauge and compute the
maximum amperage. If you see only two wires, rather than three, running to the service head or
emerging from underground conduit, there’s no hope. Three wires are required for a modern 240-volt
electrical system.

•Second, check the manufacturer’s data plate or service disconnect. It will identify the maximum
amperage of the main electrical panel.

•And third, the main circuit breaker will be marked with an amperage rating. It’s always the same or less
than the service drop and electrical panel.