ground screws in metal boxes

[Energize]

Noticed something I need another view on in a commercial application Not my job, got rained out and just visiting a buddy when inspector showed up. 4 square metal boxes ran back to back. Have a chase nipple connecting in the center of the boxes with a lock ring on either side. On one side, there is a green ground wire attached to a green ground screw in the back of the box (typical). The other side has ?.nothing.

The MC is installed on the box without the ground wire. The inspector said it was fine, as the MC had a ground inside and they could pigtail from that in one side and feed it through to the other, using the chase nipple as the continuation of the ground.

I always thought 250.148 (C) meant you had to use the screw or a clip. Inspector says the chase nipple, the ground wire in the MC cable and/or the MC flex conduit satisfies the ?listed grounding device? requirement in this section.

Thoughts?

 

[Physis 3]

From what you've said the nipple between the boxes satisfies the bonding between those two things but if you're using MC or NM you'll need to land the grounding conductors for every cable.

I'm not really seeing an issue here other than, why is your inspector allowing your cable grounds to not be landed on the rough in?

 

[raider1]

I agree with you,

250.148 requires that when circuit conductors are spliced within a box, or terminated on equipment within or supported by a box, any equipment grounding conductor(s) associated with those circuit conductors shall be spliced or joined within the box or to the box in accordance with 250.148(A) thorugh(E).

So if I have an EGC of the wire type and I splice or terminate the circuit conductors within a metal box I must also connect the EGC to the metal box in accordance with 250.148(A)

Chris

 

[al hildenbrand]

Energize,

What kind of devices are spec'ed for your friend's job? Are they auto-ground?

If so, an auto-ground device(s) in the box without the ground screw would be fine, as the chase nipple and box extend the MC EGC to the device.

There wouldn't even be the need for a pigtail in the box with the ground screw if auto-ground device(s) are used in it also. The MC EGC would only need to be under the ground screw or clip in the box the MC is connected to.

Just a thought.

 

[celtic]

Inspector says the chase nipple, the ground wire in the MC cable and/or the MC flex conduit satisfies the “listed grounding device” requirement in this section.

Thoughts?

I think the install is fine...the nipple would carry the ground as per 250.118 ..HOWEVER...I question the MC's suitablity to be called an EGC ~ is it listed and labeled as such: 250.118(11)

 

[Dennis Alwon]

The nipple is no different than a piece of emt between the boxes. A ground wire may be desired or speced but it is not necessary to be code compliant. Basically you have changed raceway methods from the mc to the nipple. The second box would only require a bond from the box to the device if you were installing a device that required grounding.

 

[al hildenbrand]

I question the MC's suitablity to be called an EGC ~ is it listed and labeled as such: 250.118(11)

Huh?

the MC had a ground inside and they could pigtail from that

250.118 (10) . . . is there MC with a ground wire that is not an EGC that is easy to get?

 

[iwire]

I agree with Chris.

Each box needs a ground screw no matter how redundant the chase nipple makes it.


BTW.......I think Ryan pointed out before that chase nipples are not listed for grounding but I may well be mistaken about it.

 

[Dennis Alwon]

BTW.......I think Ryan pointed out before that chase nipples are not listed for grounding but I may well be mistaken about it.

The OP said chase nipple but also said there was a locknut on either side. I took that to mean a nipple.

BTW-- I think you are correct about chase nipples not being suitable for grounding. I heard that somewhere also.

 

[celtic]

I question the MC's suitablity to be called an EGC ~ is it listed and labeled as such: 250.118(11)

Huh?250.118 (10)

I think I missed the word sheath there :roll:...the sheath of the MC must be listed and labeled per 250.118(10)

. . . is there MC with a ground wire that is not an EGC that is easy to get?

I dunno :grin:...but there is MC w/o a ground that has the sheath listed as an EGC that is easy to get.


(I really need to stop referencing the '02 ~ 250.118(11) is 250.118(10) in the '05)

 

[jerm]

The MC is installed on the box without the ground wire. The inspector said it was fine, as the MC had a ground inside and they could pigtail from that in one side and feed it through to the other, using the chase nipple as the continuation of the ground.

As I read the OP, the mc goes into the box on the back of the box with the ground screw- that is, it terminates into a box without a ground screw. While the chase nipple continues the ground from the box with the ground screw to the box without (just like emt would), the MC's ground must make up to the box it terminates in, not the "next box down the line", per 250.148:

250.148 requires that when circuit conductors are spliced within a box, or terminated on equipment within or supported by a box, any equipment grounding conductor(s) associated with those circuit conductors shall be spliced or joined within the box or to the box in accordance with 250.148(A) thorugh(E).

I say the inspector got it wrong. Every box with any MC terminating into it requires a ground screw.

 

[al hildenbrand]

there is MC w/o a ground that has the sheath listed as an EGC that is easy to get.

Yup.

With auto-ground devices, there's no ground wire, screw or clip to muss with in generic settings.

 

[lordofpi]

BTW.......I think Ryan pointed out before that chase nipples are not listed for grounding but I may well be mistaken about it.

Let us take MC out of the equation for a moment and consider an EMT run where the entire circuit is permitted to use the EMT as the EGC path per Article 3xx.xx (see how good my memory is). For the sake of argument, the EMT terminates into a junction box and then a few nipples go out to a couple of adjacent 4" square receptacle boxes (all metallic). Surely the connections of the receptacles to the EGC-path will be made by a pigtails to grounding screw in their respective boxes, thus it follows that the nipples must be an approved grounding path.

I've implemented variations of this scenario countless times in service work wherein an EGC was never pulled by the original installer and the EMT is the grounding path, and I nipple some receptacles off of a junction box. Be this non-compliant, I am willing to hear it; no inspector has yet to cite it.

 

[jerm]

where the entire circuit is permitted to use the EMT as the EGC path per Article 3xx.xx (see how good my memory is).

358.60. One of my favorites. Stupid green #12 required in EMT by architects, not NEC...

 

[Jim W in Tampa]

358.60. One of my favorites. Stupid green #12 required in EMT by architects, not NEC...

I dont see it as stupid and wish it was required.EMT by itself may or maynot work.So much as one piece comes loose and we have no ground.I never ever run emt without a green

 

[jerm]

CMPs for the last 100 years (or so) disagree with you. EMT is good enough.

 

[lordofpi]

358.60. One of my favorites.

Haha, "one of my favorites" -- it sounds like we are quoting verses of Hamlet or the Bible.

Hmmm... you know, I was reading through Article 110 today, and I was really moved by Section 110.12. I mean, the poetic language really struck me, and the use of metaphor -- "neat and workmanlike" is like, you know, an allegory for the archetype of what it means to be an electrician.

 

[Jim W in Tampa]

CMPs for the last 100 years (or so) disagree with you. EMT is good enough.

Have you never seen it where it comes apart ?Now if its a metal building chances are high that building steel will pick it up.Thankfully its not an issue for me as by boss requires it even if specs dont.Any man on my crew will learn fast,simply is no need to be that cheap or lazy.If someone gets hurt or killed its not the cmp's they sue

 

[jerm]

Haha, "one of my favorites" -- it sounds like we are quoting verses of Hamlet or the Bible.

lol... one day on break we started re-writing the NEC in KJV. An ambitious project, yes.

110.12 "And the Lord came down and saw the neat and workmanlike manner in which it had been done, and He said 'It is Good and Well, that they may all be safe and powered with 120 volts"

"Honour thy Hot and thy Neutral, make them ungrounded and grounded. Inasmuch as you do this unto them, it shall be done unto you."

 

[jerm]

Have you never seen it where it comes apart ?

People get sued all the time. If it meets code then it doesn't matter and that's a weak response.

Law of inertia says that EMT screws that are made up properly won't spontaneously unscrew themselves. EMT screws that are unscrewed are the result of LAZY electricians who didn't bother screwing them in the first place. Electricians using EMT as a grounding means are not lazy.

You think it's so unsafe then submit the proposal to change it. It will be rejected like all those before it as there are no grounds (pun not intended).