Field Grounding vs. Factory Grounding

FlyWhale

Member
Location
USA
Occupation
Electrician
Hello all, I am having trouble understand the code reference to installing a ground lug in an enclosure. In this case it's a disconnect. I understand you have to scrape the surface clear of any paint or other similar coatings to ensure a good ground connection. When a disconnect is sometimes supplied with a nuetral bar kit, it has an option to be grounded with a ground screw that is supplied with the disconnect. The neutral bar kit is mounted with a plastic isolation bracket. This means that if I install the ground screw to bond the nuetral bar kit.....it's only grounded through the threads in the enclosure bad by the thread-forming ground screw. I'd like to install a double barrel lug to ground everything. What I don't understand is why I have to scrape the paint off the enclosure and yet if I just use the nuetral bar kit as a ground bar (no nuetrals involved...just ground) a threaded tap will be just fine. Aren't I basically doing the same thing by tapping the enclosure? Is just a different lug, isn't it? I've heard before it has to do with UL listing but it still doesn't make any sense to me.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
there is no need to scrap the paint. that is an old wive's tale.

the threads are what makes the connection. as long as you use a fine thread screw, it will be ok.
 

FlyWhale

Member
Location
USA
Occupation
Electrician
there is no need to scrap the paint. that is an old wive's tale.

the threads are what makes the connection. as long as you use a fine thread screw, it will be ok.

Ok, I see. I'm looking at 250.12
A part of the last sentence says...."or be connected by means of fittings designed so as to make such removal unnecessary". What are some fittings that would fit this description?
 

Nuber

State Certified Practitioner of Electrical Arts
Location
Colorado
Occupation
Master Electrician
there is no need to scrap the paint. that is an old wive's tale.

the threads are what makes the connection. as long as you use a fine thread screw, it will be ok.
I would disagree - 250.12 clearly states that non-conductive coatings shall be removed from threads AND other contact surfaces

OR

be designed by means of fittings to make such removal unnecessary - a machine screw is not a fitting and does not comply.

When you have a factory listed assembly, installing it in the manner described in the instructions (a factory ground bar) has been listed to be used in that manner 250.8(A)(7). Compliant via listing.

When installing a field bond or grounding you are using 250.8(A)(5) or (6) and the paint must be removed from the contact surface for the bond or grounding.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I would disagree - 250.12 clearly states that non-conductive coatings shall be removed from threads AND other contact surfaces

OR

be designed by means of fittings to make such removal unnecessary - a machine screw is not a fitting and does not comply.

When you have a factory listed assembly, installing it in the manner described in the instructions (a factory ground bar) has been listed to be used in that manner 250.8(A)(7). Compliant via listing.

When installing a field bond or grounding you are using 250.8(A)(5) or (6) and the paint must be removed from the contact surface for the bond or grounding.
there is no paint to be removed from where the threads are. the contact surface is the threads.
 

Nuber

State Certified Practitioner of Electrical Arts
Location
Colorado
Occupation
Master Electrician
there is no paint to be removed from where the threads are. the contact surface is the threads.
Just don't agree. The code clearly states "and other" in the requirement after describing the threads. That means they are referring to something other than the threads.

In any case around my neck of the woods, you will never pass an inspection if you don't scrape the paint when you are bonding the can. Never.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Just don't agree. The code clearly states "and other" in the requirement after describing the threads. That means they are referring to something other than the threads.

In any case around my neck of the woods, you will never pass an inspection if you don't scrape the paint when you are bonding the can. Never.
I agree, if you're field installing a terminal the paint needs to be removed. If the terminal if tested and listed by the manufacturer to simply rely on the screw for the connection then the paint can remain.
 

Nuber

State Certified Practitioner of Electrical Arts
Location
Colorado
Occupation
Master Electrician
I agree, if you're field installing a terminal the paint needs to be removed. If the terminal if tested and listed by the manufacturer to simply rely on the screw for the connection then the paint can remain.
Isn't it crazy how we must think like lawyers at times to do our jobs? Petersonra's type of installation would probable function as intended, yet all of us schmucks in the field have to take the paint off while a worker in a factory can drill and tap the hole, then paint the can anyway.

Kind of silly really, but that is how the code reads.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Isn't it crazy how we must think like lawyers at times to do our jobs? Petersonra's type of installation would probable function as intended, yet all of us schmucks in the field have to take the paint off while a worker in a factory can drill and tap the hole, then paint the can anyway.

Kind of silly really, but that is how the code reads.
The factory guy is installing it in the same way that it was tested in a lab. If you drill a hole and nut and bolt the terminal to the paint there is no way of know whether or not that will be sufficient to carry the fault current. It's accepted that if the paint is removed and metal to metal contact is made that the connection should be sufficient to carry the fault current.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
The factory guy is installing it in the same way that it was tested in a lab. If you drill a hole and nut and bolt the terminal to the paint there is no way of know whether or not that will be sufficient to carry the fault current. It's accepted that if the paint is removed and metal to metal contact is made that the connection should be sufficient to carry the fault current.

250.8 Connection of Grounding and Bonding Equipment.
(A) Permitted Methods. Equipment grounding conductors,
grounding electrode conductors, and bonding jumpers shall be
connected by one or more of the following means:
(1) Listed pressure connectors
(2) Terminal bars
(3) Pressure connectors listed as grounding and bonding
equipment
(4) Exothermic welding process
(5) Machine screw-type fasteners that engage not less than
two threads or are secured with a nut
(6) Thread-forming machine screws that engage not less than
two threads in the enclosure
(7) Connections that are part of a listed assembly
(8) Other listed means
Seems like (5) specifically allows it.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Seems like (5) specifically allows it.
Yes it does after the paint is removed.
250.12 Clean Surfaces. Nonconductive coatings (such as paint, lacquer, and enamel) on equipment to be grounded shall be removed from threads and other contact surfaces to ensure good electrical continuity or be connected by means of fittings designed so as to make such removal unnecessary.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Wouldn't the two thread engagement qualify as a "means of fittings designed so as to make such removal unnecessary"?
Is a screw a fitting? Even if it is it would need to be designed for the purpose like when you purchase an equipment ground bar fr a panel and it comes with the mounting screws. If you drill a hole for a nut and bolt the paint is required to be removed.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Is a screw a fitting? Even if it is it would need to be designed for the purpose like when you purchase an equipment ground bar fr a panel and it comes with the mounting screws. If you drill a hole for a nut and bolt the paint is required to be removed.
I think a screw meets the definition of a fitting. Go look at the definition.

Besides I don't see how you can claim that something that is specifically allowed by the code is somehow not allowed due to an old wives tale.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
I've wondered in past the bonding in a painted box with ground applied as suggested by screw only, tested continuity from cover screw to main ground conductor at breaker panel, reading 0.003ohm, on tone setting I get tone, seemed to be bonded to me.
Also think about a breaker panel that has optional g/n bonding by installing the green screw, the only thing making the bond is the screw threads.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
By the way, I am not suggesting that this practice is in any way harmful, and I understand that it may be a common thing and in the grand scheme of things a little bit of extra labor is not that big a deal. But I question whether it's actually required by the code.

How many of you remove the paint from beneath an accessory ground bar kit if you end up installing one in a panel board? I bet you there aren't all that many people that remove the paint from the threads before they install the accessory ground bar kit.

How many remove the paint from around a knockout hole when you enter a box?
 

Nuber

State Certified Practitioner of Electrical Arts
Location
Colorado
Occupation
Master Electrician
I think a screw meets the definition of a fitting. Go look at the definition.

Besides I don't see how you can claim that something that is specifically allowed by the code is somehow not allowed due to an old wives tale.
In 250.8(A)(5) it specifically calls out a machine screw as a fastener - not a fitting. Old wives have nothing to do with it. Code says we must do this.
 

Nuber

State Certified Practitioner of Electrical Arts
Location
Colorado
Occupation
Master Electrician
By the way, I am not suggesting that this practice is in any way harmful, and I understand that it may be a common thing and in the grand scheme of things a little bit of extra labor is not that big a deal. But I question whether it's actually required by the code.

How many of you remove the paint from beneath an accessory ground bar kit if you end up installing one in a panel board? I bet you there aren't all that many people that remove the paint from the threads before they install the accessory ground bar kit.

How many remove the paint from around a knockout hole when you enter a box?
With sheet metal enclosures there simply isn't an easy way in the field to ensure that you have engaged two full threads. The gauge of metal and the size of the screw and the thread pitch of the screw make for a crazy field calculation. Scraping the paint - and I fully believe that it is required by code - is an additional measure to ensure positive bonding.

For me - I always scrape the paint under a field installed bar. I never scrape the paint for a raceway because I use locknuts (250.12) that do the scraping for me - they are the only kind I buy.

As you say, scraping paint isn't that much labor, but is sure isn't fun so I avoid it when I can.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
With sheet metal enclosures there simply isn't an easy way in the field to ensure that you have engaged two full threads. The gauge of metal and the size of the screw and the thread pitch of the screw make for a crazy field calculation.
250.8 Connection of Grounding and Bonding Equipment.
(A) Permitted Methods. Equipment grounding conductors,
grounding electrode conductors, and bonding jumpers shall be
connected by one or more of the following means:
(1) Listed pressure connectors
(2) Terminal bars
(3) Pressure connectors listed as grounding and bonding
equipment
(4) Exothermic welding process
(5) Machine screw-type fasteners that engage not less than
two threads or are secured with a nut
(6) Thread-forming machine screws that engage not less than
two threads in the enclosure
(7) Connections that are part of a listed assembly
(8) Other listed means
So you always put a nut on the back side as required by 250.8 (5) in lieu of the two thread engagement?

In 250.8(A)(5) it specifically calls out a machine screw as a fastener - not a fitting. Old wives have nothing to do with it. Code says we must do this.
What makes you think it cannot be both?
Fitting. An accessory such as a locknut, bushing, or other part
of a wiring system that is intended primarily to perform a
mechanical rather than an electrical function.
I think I answered my own question here. A screw is not a "part" of a wiring system.
 

Nuber

State Certified Practitioner of Electrical Arts
Location
Colorado
Occupation
Master Electrician
Ahh, word games. Fun isn't it? Caveat - this is a respectful debate - I am not trying to bust on you specifically.

So you always put a nut on the back side as required by 250.8 (5) in lieu of the two thread engagement?
Don't have to. The code says "or" if I can't get two threads. I will use a nut whenever I can get it to fit, for both mechanical and electrical reasons. I am suggesting that the code making panel many moons ago made the additional requirement, or foresaw the need to, require the paint be removed as an additional safety factor. There are some questionable decisions made in the field from time to time and requiring paint removal for a grounding/bonding scenario seems to be justified as an added precaution. This is a guess on my part that seems reasonable, I wasn't there when it was added as a part of the code. I have only been using the code since the 1993 cycle, and the paint removal requirement has been there my entire career.

What makes you think it cannot be both?

I think I answered my own question here. A screw is not a "part" of a wiring system.
As referenced, the code's own language calls such an item a fastener - if they meant fitting I believe that they would have used that word.

I believe we have found a regurgitating loophole - a black hole of code application that we will never get out of absent an update to the definition of the word fitting or a clarifying revision of 250.8 and/or 250.12.

For me, and my crews, we take off the paint because my reading of the code requires that I do. And I won't pass an inspection if I don't. If you don't remove the paint, that is up to you and your AHJ.
 
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