Grounding a Panel in a Detached Building
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The Electrical Codes for the Grounding System of a Sub Panel in a Detached Building Explained © By: Dave Rongey |
Grounding a Panel
Electrical Project: What are the Electrical Codes for the Grounding System of a Sub Panel in a Detached Building?
Eric in Arizona asks:
- I have a home with a house and a detached garage, both were built in 2000. the main panel is grounded (an ufer ground) and in the main panel the neutral and ground are bonded together. the detached garage has a sub panel. the garage has its own UFER ground. The main panel has three feeders running to the sub panel, two hots and a neutral. the hots run to the two hot legs and the neutral attaches to a neutral bar. The neutral bar is bonded to the ground bar in the sub panel, just like the main panel. I can’t see anywhere that the ground is bonded to the case at at the sub panel or the main panel.
- It is my understanding that prior to 2005, this was considered an appropriate configuration, but subsequent to 2005, a second ground was required to run back to the main panel and the ground and neutral at the sub panel should be isolated from each other and the ground should be bonded to the case.
- My question is:
Short of running that fourth wire to act as a ground running back to the panel, which would be a relatively expensive project in this particular installation (it is about 150 feet long and all the wires would have to be pulled and re-installed in order to add the fourth wire) – can I just leave this alone? - Everything I read tells me grounds and neutrals should never be bonded in a sub panel, but that seems to be wrong in an older installation like this one, is that correct? Is this configuration as safe as it is possible for it to be or is there some change I should make (again, short of adding the fourth wire, which I may do someday, but right now do not want to do).
- Also, should the case be bonded to the ground in both the main and the sub panels, or just the sub panel or neither (again, assuming no fourth wire)?
- Finally, how big should the connector be that bonds a case to the ground? I can’t seem to find an answer to that no matter how hard I try.
Thanks for your consideration.
Dave’s Reply:
Thanks for your electrical wiring question Eric.
Grounding a Sub Panel in a Detached Building
Application: Installing a Sub Panel in a Detached Building or Garage.
Skill Level: Advanced – Best performed by a Licensed Electrical Contractor, or Certified Electrician.
Electrical Tools Required: Basic Electricians Pouch Hand Tools, Voltage Tester, and appropriate Safety Gear.
Estimated Time: Depends on the personal level experience, ability to work with tools, install electrical circuit wiring, and the available access to the project area.
Electrical Safety: Identify the electrical power source to the Sub Panel, turn it OFF and Tag with a Note before working with the electrical wiring.
Electrical Wiring Parts and Materials: Electrical parts and materials for the Sub Panel should be approved for the specific project and compliant with local and national electrical codes.
Electrical Codes and Inspections: Installing or changing home electrical wiring should be done according to local and national electrical codes as adopted in Arizona. A permit and inspections may also be required.
Electrical Code for a Sub Panel in a Detached Garage
This electrical wiring project is about the NEC Electrical Code for a Sub Panel in the Detached Garage.
NEC Code Terminology Clarification:
A Detached Building refers to a building that is not physically attached to another structure. In this example, this refers to a garage that is not attached to the home.
Sub Panel Electrical Code General Question
- Eric, from the information you have provided, the 2017 NEC article 250.32(A) states that the grounding system requirements are the same for the detached building sub panel as for the main service equipment, which means an approved ground system should be installed at the detached building and the neutral and ground should be bonded together.
- Also, the 2017 NEC 230.71(A) states that if there are more than 6 circuit breakers in the detached building’s sub panel then a main breaker is required.
- It should be noted that when the electrical wiring is altered or added, the project then falls under the current electrical codes that apply, and the codes that have been adopted for the specific area and local jurisdiction.
More about Grounding a Panel for a Detached Building
The following article discusses the topic of grounding for a detached building in detail:
Installing a Sub Panel for a Detached Building
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