conduit for ground in metal shop

Question

Ive run my EMT conduit and placed my boxes in my workshop and placed the wires. All is good except… my inspector says I cant use conduit as ground and must run a bare or green conductor to each box/outlet… I dont want to get into rules/lawyering but what NEC line tells me (him) that conduit is OK for residential grounding. My city (Tucson) is on the 2017 NEC rev.

Am I reading this wrong?:

250.118 Types of Equipment Grounding Conductors.  The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:
(1) A copper, aluminum, or copper-clad aluminum conductor. This conductor shall be solid or stranded; insulated, covered, or bare; and in the form of a wire or a busbar of any shape.
(2) Rigid metal conduit.
(3) Intermediate metal conduit.
(4) Electrical metallic tubing. ...

and this:

358.60 Grounding.  EMT shall be permitted as an equipment grounding conductor.

Harper - Reinstate Monica · Accepted Answer

Yeah, that's wrong. The inspector ought to know better; clearly does not inspect a whole lot of commercial installations.
Gently stand up on the point and show him the code, and leave him a path to keep his ego intact (that is less than you pulling a bunch of pointless ground wires).  That's part of negotiating.
By the way, if you do pull the trigger on pulling ground wires, the ground wires go to the boxes not the receptacles.  They land on a 10-32 ground screw (which doesn't need to be green), which goes into the hole in the back of the box already tapped 10-32.  When bringing a ground to any metal box, you must go to the box first. Once that's done, if you also want to bring ground to the recep, you can do that also e.g. via pigtailing. #1 mistake I see grounding metal boxes.
In cases like yours, where the recep will have hard flush metal contact between its yoke and the junction box mud ring or domed cover, that is a valid grounding path and ground wires are not needed.  So remove that little paper square that captures the receptacle screw!
On switches it's even easier, you don't even need to remove the paper square and you only need screw-head contact with the yoke.

JRaef · Answer

Legal or not, it's no longer a good practice to use only the conduit as the EGC (electrical grounding conductor) because of the predominance of electronic equipment. Electroni power supplies of all kinds create Common Mode Noise and that needs a solid ground path to avoid becoming a problem in your system. As conduit connections age and corrode, it adds resistance to the ground path and CM noise finds another path, sometimes through expensive sensitive equipment. The NEC is only concerned with safety, not equipment life.

Answered by JRaef on July 12, 2021

conduit for ground in metal shop

2 Answers

Add your own answers!

Ask a Question