Page 516 - 2018 National Home Improvement

2018 National Home Improvement Estimator, All Rights Reserved Page 411

If the home has a basement, most of the service upgrade can be done there. Replace the old fuse box
or boxes with a modern breaker panel. Then disconnect circuits running to the fuse box and reconnect
them at the breaker box. Attach each circuit to a breaker with the correct capacity. The new breaker
panel should have enough breaker spaces for existing circuits, plus a few extra for expansion. Most
homes will need a 150- or 200-amp service panel.

Because the electrician’s part of the work is done in the basement or outside, it can be done after all
the carpentry and interior finishing is complete. However, any wiring that has to be run in the walls must
be completed before drywall is installed. Otherwise, electrical wire has to be fished down between the
studs.

Wiring Residences
Nearly all new homes today are wired with non-metallic sheathed cable, but that may not be what you
find when you work on an older house. Depending on its age, you may have some surprises.

Knob and Tube Wiring
Homes built before about 1930 usually had knob and tube (K&T) wiring. Wires were strung between
porcelain insulators driven into studs and joists. If wire had to pass through framing, a hollow porcelain
tube was inserted in a hole drilled through the stud or joist. Conductors were usually single strands
covered with cloth insulation. You won’t find a ground wire on K&T. In those days, only lightning rods
were grounded.

K&T that’s given trouble-free service for nearly a century could probably do the same for another
century, if no further demands were made on the system. But that’s not likely. Because it isn’t
grounded, doesn’t have enough capacity, and its insulation isn’t worthy of the name, some insurance
policies exclude coverage for homes with K&T wiring. For that reason alone, many of these older homes
have already been upgraded.

If you find K&T wiring and the owner isn’t willing to replace it, just by-pass the K&T. Work around it with
new circuits. Don’t extend it. If possible, don’t even touch it unless you find an actual or impending
emergency.

Aluminum Wiring
Aluminum wire is another type that’s no longer used for interior home electrical systems. Aluminum is a
good and durable conductor and is usually less expensive than the more popular copper. However, late
in the 1970s, electricians and code officials began to recognize a problem developing in homes with
aluminum wiring. When aluminum wire carries current, it warms up and expands, just like copper. When
it cools, the aluminum contracts, just like copper. But unlike copper, aluminum connections oxidize
during the cool-down phase, creating resistance where conductors join. With time, the resistance grows
into arcing – a spark that passes through the corrosion (gap) between the wire and the connector. Given
the right conditions, that spark can ignite a fire.