Residential Grounding & Bonding

By Brian Tregoning


What are grounding and bonding?  This is one of the easiest hard questions to answer.  Even electricians find it difficult to follow and keep current the extensive NEC codes.  As a homeowner you are not expected to know the entire code, that’s why we have electricians that are licensed.  This article is meant for informational purposes only for the homeowner and is not an exhaustive overview of the actual electrical code.  Always consult a qualified electrician with questions or before modifying your homes electrical system.

Now that we have the disclaimers out of the way, let’s start with grounding. There are many definitions for grounding but, I prefer the definition of grounding according to National Home Inspection Manual. It states that “Grounding provides an alternate path for current to return to its source, in an electrical power system, the source is the transformer belonging to the utility company, and ultimately the power plant.”  Essentially the grounding system helps deal with uncommon voltage surges such as lightning or if a higher voltage circuit contacts the electrical system.  The grounding system simply provides a safe low resistance path to dissipate those uncommon surges or mishaps that may accidentally charge a metal object such as a refrigerator cabinet or your new flat screen. 

Generally, bonding has the biggest impact for a homeowner at the outlets and switches, also referred to as branch circuits.  If your home was built after the early 1960’s you will most likely have outlets with three slots.  These are bonded/grounded outlets and you are good to go for modern electronics. (Beware, it is easy to put a three prong plug on a two-wire system and the plug will operate just fine but, it is still a two-wire plug.  (If you are not sure your house has grounded plugs you can pick up an inexpensive outlet tester at your local hardware store.)   Until about 1960, grounding was found only at the service panel (electric box).  Up to then, most homes operated on a two-wire system that only consisted of 1 hot and 1 neutral wire.  These two wire systems utilized plugs with only two slots.  These two slot plugs were the common practice for years and are not technically “wrong”, they are just not grounded and therefore, do not have the added protection of a grounded plug.  This makes the two prong outlets more susceptible to power surges and electric shocks.  This can result in electrical shock to your fingers when plugging or unplugging a cord, mostly it is a detriment to all the modern electronic devices such as computers and TVs that are susceptible to surges.  If you have a two-wire system currently and would like to have the benefits of grounded outlets, you have two options. You can upgrade your electric system or you can install a GFCI circuit breaker in the electrical panel or a GFCI outlet at the first outlet from the electric box.  In short, grounding/bonding gives electricity a safe place to go if there is a surge or something that should not be electrified is electrified by accident.

Grounding and bonding are often thought of as similar terms and often mistakenly used interchangeably.  Although they are used in conjunction with each other, they have distinctly different roles.  As we discussed above, grounding provides a safe path to ground for excess electricity.  Bonding is described in the NHIE Home Inspection Manual as, “The process of connecting, both physically and electrically, all metal components of the electrical system that are not intended to carry electrical current.  While grounding gives a low resistance back to its source, bonding ensures that any metal components in the home all have the same electrical potential.  There is a myth that electricity takes the path of least resistance, the reality is it takes all paths.  By bonding all the metal components together such as water and gas piping everything bonded has the same electrical potential.  Higher voltage is not passed to a lower voltage path because it all is equal. If someone were to create a ground fault, (grabbing a toaster while doing dishes,) the electricity will all return back to its source utilizing everything that is bonded together, the first stop being at the breaker or fuse.  Just think about those tall power lines with birds perched from one end to the other.  By sitting on one wire they are not touching any anything of a different potential.  Therefore, the electricity will not flow through them and they live to fly south for another winter.

For the homeowner, this translates down to this.  Grounding acts as a surge protector for the home when unpredictable things happen.  Bonding makes everything have the same potential so you do not become the low resistance path to ground.


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