Grounding and Bonding of electrical remote or sub panels in detached buildings
(HawleyHomeInspectionsLLC.com) Grounding and bonding is required with the exception of outbuildings containing only one 120 volt grounded branch circuit. Electric systems at detached buildings require bonding and a separate grounding electrode system (GES),which is commonly a grounding electrode (ground rod) in our area. See attachment for wiring illustration. One illustrates a 3 wire feeder and one illustrates a 4 wire feed.
When inspecting the service panel (main breaker/fuse box) you will need to determine that it is the first disconnect in the system downstream from the meter. There are two common exceptions.
The first would be in rural systems where the meter and a service panel / disconnect are located on a pole and not the house or shed and are more than ten feet apart.
Second the meter and inside breaker panel may be separated by a considerable distance (usually 10 feet or more) with a disconnect located directly below or close to the meter.
The second is most often found in duplexes and apartments but may also be the result of adding a garage or room addition and moving the meter but not the breaker box. In this case a disconnect is located near the meter. Make sure the service wires to the remote are in conduit.
Grounding and Bonding for Remote or Sub Panels
In both of the above cases what most people would refer to as the main breaker panel is actually a “remote panel” (please use remote not “sub panel”). If the wires feeding the remote panel are H H N G it is a 4 wire feed and neutrals must be isolated and grounds separated and bonded to the panel body.
If it is a three wire feed H H N no ground from the supplying panel (this includes metallic conduit) then it is a 3 wire system. A three wire remote panel is treated the same as a service panel with grounds and neutrals allowed on the neutral buss. (Otherwise there is no connection to ground).
In this case the neutral bus containing both neutrals and ground wires would be bonded to the panel body. We recommend upgrading a three wire system to a 4 wire system for safety.
To be clear ground rods do not provide ground fault clearance for the breakers. The earth ground will only allow about 4.8 amps to flow to ground at 120 v and this will only energize the ground wire but will not trip a breaker. The ground rod is to help dissipate electricity overloads from lightning strikes and power surges.
Grounding and Bonding Requirements
Grounding and bonding requirements are set by the National Electrical Code. However there are many different acceptable grounding options from metallic water pipes, driven ground rods, buried ground rings and using the rebar in a foundation. Each method must be approved by the local code officials due to the different soil types and moisture contents around the country.
Three wire feeds were allowed by the National Electrical Code until the 2008 edition. The NEC, as with all codes is constantly changing as new problems and solutions are reviewed. Many municipalities do not adopt the current code (new) for several reasons.
It is common practice for the authority having jurisdiction (AJH) to wait and see if the new changes to a code are revised, removed, modified or generally accepted by other jurisdictions. This may mean the local AHJ may be three to twelve years behind the current code cycle.
With a few exceptions code changes usually only apply to new construction and/or remodeling work that requires a permit.
We recommend reviewing any electrical issue with a qualified electrical contractor. Many issues are involved in upgrading an electrical system. Cost must be weighed against possible safety issues and the benefits to be gained.
Some changes are relatively inexpensive and can have a very large affect on safety and efficiency and others may require extensive demolition and reconstruction with little if any improvement in safety or efficiency.
The other issue to consider is whether the local code enforcement officials (AHJ) will require the upgrade. The National Electrical code is only a standard put out for everyone to use. The enforcement to the code is up to the city, township, county or state you live in.
Safety is always a top priority when dealing with electricity because it does not care were it goes or how it gets there. Nor does it care if it gets their by way of human contact. We will never be able to make electricity completely safe but upgrading to current code standards when possible will go a long way towards saving lives and property.