ground screws in metal boxes

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jerm said:
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).
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I can just see you exsplaining this in court.If they are all tight then it didnt come apart.How will you exsplain the one that did come apart ?Guess one of your men missed one (it does happen).But thats fine keep doing as you wish and i will keep runing a ground.Our company is not the low bidder.We offer a bit more than required.
 
al hildenbrand said:
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.
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They are not auto ground, just regular, small-square-of cardboard- holding the -screw receptacle. And no, the cardboard was not removed in these flush mounted receptacles.
 
Dennis Alwon said:
The OP said chase nipple but also said there was a locknut on either side. I took that to mean a nipple.
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There is a total of two locknuts - one in each of the boxes, intended to push the boxes towards each other.
 
jerm said:
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:
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That is the correct situation.


jerm said:
I say the inspector got it wrong. Every box with any MC terminating into it requires a ground screw.
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I agree, just never heard of this until today.
 
Chase nipples are not listed for grounding/bonding. Our inspectors will fail it even with locknuts on both sides, don't ask me how I know. We have to use pipe nipples with locknuts and plastic bushings, or else land the EGC in each enclosure.
Some guys like to take off with an LB using a chase nipple and a locknut on the inside, but it won't work for our inspectors.
 
One of the parts I don't get about this is why bother using one EGC terminted to the ground screw? I would have thought you either used two or none, depending on if you find the nipple acceptable. Weird.

Wasn't my job so I did not want to butt in or take any of the inspectors time, but it sure raised my eyebrows...
 
Energize said:
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.
Thoughts?
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I do this all the time! Chase into the adjoining box, and pig-tial one ground into the other, and pig-tail those with one to a ground screw. Often with 1900's, the screw will even go through to the other box anyway not to mention be effectively grounded by the nipple and direct contact to the other box. Technicaly the EGC's all all tied together anyway, and the box without a green screw by 250.118 via 250.136. I see this as no different than the fact that there is no EGC connected to the plaster ring either, all are firmly in contact with eachother, and all supplimented by an EGC as a fault path.

Either way, if you did need to put a silly green screw in each box you would need to tap both.
 
Jim W in Tampa said:
....I never ever run emt without a green
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We will omit the green conductor on jobs where the building is all steel, and all boxes, straps, etc. are fastened directly to the steel.

We will not omit it, however, in other cases where the EMT can become isolated from the steel infrastructure.
 
Chase nipples are not accepted as grounding nipples here either. Nipples are ok but not chase nipples no matter how many nuts are on them. As for the green wire in EMT, I put it in if the customer specs it and pays for it. I won't bid putting in there against other contractors who don't. And copper is getting way to expensive to throw it in for free. EMT is listed and accepted as an EGC. That is good enough for me.
 
Metal raceway actually has less impedance than a copper EGC, assuming the raceway is mechanically continuous/sound.

However, I need a reference for this (I've heard it on the forum but I can't remember where/when.)
 
Found this guy (This thread had me wondering... I have a few on the truck right now - yet to use one....
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From the Arlington fittings site....
Arlington's metallic SNAP-TITE? products have been tested and listed by UL in accordance with UL's ground fault requirements.
N.E.C. 2002. 250-97. Bonding for over 250 volts. For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in Sections 250-94(1) through (4). Exception: Where oversized, concentric, or eccentric knockouts are not encountered, or where concentric or eccentric knockouts have been tested and the box or enclosure is listed for the use, the following methods shall be permitted:
  1. Threadless couplings and connectors for cables with metal sheaths.
  2. Two locknuts, on rigid metal conduit, or intermediate metal conduit, one inside and one outside of boxes and cabinets.
  3. Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors, flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets.
  4. Listed fittings.
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From thier justification a chase nipple would fit "c" above....
 
Here's something to think about: (I ran into this in the field once)

Mount two 1900's back to back, with a chase or close nipple between them. Use the old style boxes before they started raising up the ground screw hole- remember those? Align the ground screw hole so that you can access it from the *other* box.

Use a ground screw in the front box, screwed into the threaded hole in the back box. Now your copper is physically against and inside the front box (and the head of your screw is in there too) but you're grounded via threads to the back box.

What code would this violate (110.12 is a cop out, don't give me that) and which box is your stinger really grounding to?

(answers: 1. I don't know 2. your stinger is outside the box it grounds to I think. That's got to be a violation of some sort.)

BONUS QUESTION: What year did the 1900 manu's start raising the ground hole up?
 
e57 said:
Found this guy (This thread had me wondering... I have a few on the truck right now - yet to use one....
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From the Arlington fittings site....
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I've never seen those. But I like the looks of it. Does it say it's listed for grounding on the box they come in?
 
Those are called "spacing nipples" I believe.

It would seem, based on the information I've seen, that nipples with threads on both ends (i.e., requiring locking bushings on both ends) are listed for grounding, while chase nipples are not. For instance the spacing nipple or an offset nipple is okay. Am I close to being right about this?
 
OK Who says chase nipples are not approved for grounding - SHOW YOUR SELF!!!! :grin:

Someone said 'Ryan' earlier (same Ryan of whom at one point mentioned that green 'Ground' screws are not listed?) - if so please justify this with something before internet lore becomes law of the land....

I see it as no different than any other die-cast fitting with shoulders that rest firmly against the box, and a lock-nut on the other side....
 
e57 said:
OK Who says chase nipples are not approved for grounding - SHOW YOUR SELF!!!! :grin:

Someone said 'Ryan' earlier (same Ryan of whom at one point mentioned that green 'Ground' screws are not listed?) - if so please justify this with something before internet lore becomes law of the land....

I see it as no different than any other die-cast fitting with shoulders that rest firmly against the box, and a lock-nut on the other side....
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Actually I said it. But what I should have said was "Our inspectors insist chase nipples are not APROVED for grounding/bonding"
 
Jim W in Tampa said:
Have you never seen it where it comes apart ?
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Yes.

Have you ever seen a splice come apart?

I have seen many more instances of splices coming apart then conduits coming apart.
 
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