The Difference Between Electric Service Grounding
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 mainservice panel must be joined together and bonded to the panel
- The ground and neutral busses in a sub panelmust be separate
- All electric sub-panels must be supplied with 4 wire conductor feeder
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