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Electric service grounding employs a conductor that
provides a low impedance path to the earth. The ground protects
equipment and most importantly people. The ground conductor from the
main service panel ground lug or bus should be attached to an 8’ long
copper rod driven completely into the ground and connected to another
8’ long driven rod at least 6 feet apart. The connection should be
secure and protected. It is recommended that the ground conductor is
copper and not spliced. The proper size for 150 amp service is #6 AWG.
Over 150 amperes should be #4 AWG.
Bonding refers to joining two or more electric
conductors together.
Bonding provides protection by connecting all of the
metal parts (Gas pipe, water pipe, metal cased equipment, etc.) that
are not supposed to carry current and bringing them together to the
same electrical potential. No current flow can take place between
bonded components because their potential is equal. When all electrical
conductors, including people and equipment, have the same electrical
potential, no discharge can occur. Bonding by itself does nothing to
protect equipment unless the bonded wire is also connected to the
system ground. Bonding creates a low impedance path back to the source,
forcing a large current flow, which will cause the fuse to blow or the
circuit breaker to trip.
A bond conductor should extend from the main service
panel to the water pipe. We recommend the connection is made at the
street side of the meter on a metal pipe because many houses are
plumbed with plastic pipe. Even if a house is mostly metal pipe, a
dielectric union or a section that was replaced with plastic will
interrupt the ground path. A bond wire should be connected between the
cold & hot water pipes and the gas service. Obviously if the water
pipes are plastic type this would not apply. In this case, a bond
conductor would be attached from the metal water pipe where the initial
bond from the panel was made.
What should a home inspector be looking for?
- A
ground conductor from the main electric service panel properly connected
to two driven rods (you will only see one because the rods are joined
underground)
- The
connection on the ground rod should be secure and in an area where it can
not be damaged (unlike the photo)
- A
bond conductor from the main electric service panel to the water pipe,
preferably the street side of the meter (see photo)
- A
bond connection (often times near the hot water tank) joining the cold
& hot water pipes and gas pipes (see photo)
- All
CSST pipe should be grounded with no smaller than a 6 AWG copper wire or
equivalent. The length of the grounding conductor should be less than 75
feet.
- Gas
pipe should never be used as a ground
- The ground
and neutral lug / bus in the main
service panel must be joined together and bonded to the panel
- The
ground and neutral busses in a sub
panel must be separate
- All
electric sub-panels must be supplied with 4 wire conductor feeder
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