Conduit / Best practices for a shared ground between branch circuits in residential?

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viggy

Member
Location
California
Occupation
engineer
According to NEC 2014 250.130 :

Article 250 - Grounding and Bonding
VII. Methods of Equipment Grounding

250.130 Equipment Grounding Conductor Connections. Equipment grounding conductor connections at the source of separately derived systems shall be made in accordance with 250.30(A)(1). Equipment grounding conductor connections at service equipment shall be made as indicated in 250.130(A) or (B). For replacement of non–grounding-type receptacles with grounding-type receptacles and for branch-circuit extensions only in existing installations that do not have an equipment grounding conductor in the branch circuit, connections shall be permitted as indicated in 250.130(C).


(C) Nongrounding Receptacle Replacement or Branch Circuit Extensions. The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension shall be permitted to be connected to any of the following:
(1) Any accessible point on the grounding electrode system as described in 250.50
(2) Any accessible point on the grounding electrode conductor
(3) The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle or branch circuit originates
(4) To an equipment grounding conductor that is part of another branch circuit that originates from the enclosure where the branch circuit for the receptacle or branch circuit originates
(5) For grounded systems, the grounded service conductor within the service equipment enclosure.
(6) For ungrounded systems, the grounding terminal bar within the service equipment enclosure

This allows for a non grounded branch circuit to borrow a ground from another branch circuit.

My question would be what would be the best way to bond it? Run THHN inside a conduit? Is a conduit necessary? Is bare copper bad? Should I use a bonding lug on the outside of a box? Should you wrap the conduit in green tape? Can you use green THHN without a conduit? Is it bad to use romex and just cut off the non-grounding wires?

I'm trying to think of the best way to do it without confusing future electricians too much.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Welcome to the forum.

Interesting questions. As for the wiring method, there's no one best answer.

It would depend on the existing wiring method(s) in use, and the construction of the building.

Do you have a specific installation situation here?
 

viggy

Member
Location
California
Occupation
engineer
Do you have a specific installation situation here?

I have an opportunity to ground some old circuits after a new panel installation, and new circuits ran from it (with ground) to a blower/heater unit and a bathroom remodel.

The home was built in the 50s and is mostly 2-wire (non ground) with that grey fabric weaved insulation. However through the years some of the end-connections were replaced with modern romex (for switches, new lights, receptacles) with ground connections in place. Just trying to "complete" the ground runs here.

Shared ground bonding would occur in the attic crawlspace between junction boxes.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
So, it's NM wiring in a residence. Is this part of your job, or is it work on your own home?

They're understandably concerned here with providing how-to information to DIYers who are not professionally qualified.
 

viggy

Member
Location
California
Occupation
engineer
Well that's understandable. If information is only available to licensed electricians here, I'll go look for other sources.

Thank you for your time
 

Dennis Alwon

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I am closing this thread, in accordance with the Forum rules. This Forum is intended to assist professional electricians, inspectors, engineers, and other members of the electrical industry in the performance of their job-related tasks. However, if you are not an electrician or an electrical contractor, then we are not permitted to help you perform your own electrical installation work.

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