SYSTEM SIZE: Most modern electrical systems
are at least 100 amperes for small homes, 200 amperes for
average homes (1,500 to 3,000 square feet), and 400 amperes for
very large homes. However, other sizes such as 125 amperes, 150
amperes and even 300 amperes can be found. Very old homes may
still only have a 60 amperes service.
So how do you tell? In most modern homes, the
main breaker inside the electric service panel generally is
marked with the amperage for that panel. This is generally the
maximum service coming into the home. Note that locating and
opening this panel will often reveal a final electrical
inspection sticker giving insight into when the home was
constructed, however, don’t be fooled by an inspection sticker
for a later addition to the home. The electric inspection
sticker will also often list the amperage of the service. In
older homes, the panel maybe a split-type system with no single
main breaker. In this case, look for an overall rating on the
inside door of the panel provided by the panel manufacturer.
The main entrance cable (from the electric
meter to the main panel) also provides clues into the size of
the electrical service; generally, the larger the cable, the
larger the service entering the home. The next time you are in
one of the larger lumber yards or electrical supply houses, look
at the service entrance cables sizes and their appropriate
amperages. Most modern entrance cables use aluminum wire which
is generally larger than copper counterparts for the same
amperage (aluminum is typically used due to its lower cost).
Also, don’t confuse voltage and amperage.
Voltage and amperage can best be understood by the water hose
analogy. Voltage is similar to the water pressure. Amperage is
similar to the amount of water flow. All modern electrical
systems utilize 120/240 volt systems in the home. In extremely
old homes it is possible to find 120-volt only systems, however,
these are rare and you will likely not encounter one. Electrical
systems supplied from ground-mounted transformers will be
120/240 volts based on their age. Older, overhead systems
typically will have three main conductors coming from the pole
to the house and indicate a 120/240-volt system. In the rare
case of a 120-volt system, only two main wires feed from the
pole to the main house.
MAIN SERVICE PANELS: The main service panel
provides protection for the interior wiring of the house in the
event of an electrical short or other excessive current draw.
The size of the wiring in the home as well as the rating of the
devices attached to the wiring, determines the maximum amperage
each circuit can carry. Resetable circuit breakers, or
disposable fuses in older homes, provide the safety feature to
prevent excessive amperage from flowing in any given circuit. If
the maximum amperage is exceeded due to a faulty breaker or
fuse, overheating of the wiring and/or devices can occur
resulting in a fire or damage to the devices connected to the
circuit.
NEVER OPEN A MAIN ELECTRIC SERVICE PANEL
BEYOND THE MAIN DOOR. Inside the main service panel, there are
many exposed points of contact that are virtually un-fused and
contact with them could cause serious injury or death.
It has been our experience that a number of
home insurance companies are requiring older fuse style panels
to be upgraded to more modern breaker systems before insuring
the home. You should also be aware that several breaker style
panels, such as Federal Pacific Stab-Lok, Zinsco, etc., are
considered by some experts to be defective and potentially
hazardous. The breakers have been shown to fail under certain
electric fault conditions leading to wire overheating and a
potential fire hazard. Breakers have even been known to pop out
of the panel when the cover was removed. Replacement with a new
panel is recommended.
OLDER WIRING: Most modern homes contain Romex
style interior wiring. This style of cable has been in general
use for more than 30 years and replaced a previous similar
fabric jacketed cable. Romex style cable contains two main
conductors and a third bare ground wire. This type of wiring is
safe and generally has been trouble free.
Older homes, from the 1950’s and 60’s
commonly used a fabric sheath cable containing two main
conductors. However, the ground wire was not always present. If
the ground wire is not present, the receptacles in the home
should be two-prong instead of the more modern three-prong
devices. If the older fabric style cable does contain a ground
wire and devices within the home are older two-prong units, they
can be easily upgraded by simply replacing the receptacle and
attaching the proper wiring. However, if a ground wire is not
present in the fabric cable, new wiring must be run for the
entire circuit.
When dealing with very old homes (more than
50 years), be alert for knob and tube wiring. Knob and tube
wiring typically utilizes a white porcelain to secure the wire
to the framing members. In addition, there are two wires each
run individually with its own tube to support it. These older
two-wire systems and the associated knob can generally be seen
in basements and attics. Often when a major rewiring has
occurred, the accessible knob and tube wiring has been replaced,
however, some may still remain inside the walls and ceilings.
Generally, the older wiring can only be seen at attachment
points within the basement or attic where the older wiring
continues up into the wall cavities. If functioning, grounded
receptacles are noted throughout the home, it is likely that
most of the knob and tub wiring has been eliminated.
Again, it has been our experience that many
insurance companies are requiring knob and tube wiring to be
replaced prior to insuring the home.
Next month we will continue our discussion of
electrical systems by addressing ground fault circuit
interrupters (GFCI), arc fault interrupters (ARI), and smoke
detectors.
