panel board as an EGC

[GoldDigger]

IMO the fact that under some circumstances the code does not require use of a grounding/bonding bushing or other special hardware to connect a raceway to a box constitutes implicit recognition that the box may then act as part of the EGC path.

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[petersonra]

So you cannot connect an EGC to a metal cabinet or enclosure? Same thing to me.

you can bond the cabinet with an EGC. I don't see anywhere in 250 where it says you can use the box as part of the EGC though, despite it being a common practice. Normally I would say the code allows you to do whatever is not prohibited but since the code restricts you to using certain things as an EGC, and a metal box is not one of them, I don't see how it is not legalistically a code violation.

 

[kwired]

You do not need a wire type jumper from EGC bar to EGC bar. When you purchase the listed EGC bar it comes with two screws to connect it to the enclosure that's all that's required. You do not even need to remove any paint the deign of the screws does that for you.

If you install the bar in a spot designed to install the bar, if installing the bar in some other spot in the panel or even some other manufacturer's bar - you may need to remove paint behind the bar.

the screws bond the bar to the box. nothing says that makes the box a legal EGC.

I am inclined to agree that it is just something that is done but actually not allowed by the code.

However, for EMT and other metal conduit, the code allows the conduit or EMT to be an EGC. I think you can make a good argument that the UL listing effectively makes the box part of the EGC since the box is part of the conduit/EMT system.

IMO, as for using an enclosure as an EGC in general, such as the situation the OP mentioned, you don't really have any good argument other than it is a common practice.

If you have a panel that contains the service disconnecting means and bonding screw installed in the grounded conductor bus, do you make jumpers from the grounded conductor bus to any EGC bars installed in the panel, or are they bonded via the cabinet? Most will say they are bonded via the cabinet and no additional jumpers are needed, if you install additional jumpers then the bonding screw shouldn't be needed, and is one way to do the bonding if you lost the screw.

 

[infinity]

If you install the bar in a spot designed to install the bar, if installing the bar in some other spot in the panel or even some other manufacturer's bar - you may need to remove paint behind the bar.

I agree that is why I initially stated the listed EGC bar with its screws from the manufacturer. Any deviation like using a lug or other EGC bar would require the paint to be removed.

 

[texie]

If you install the bar in a spot designed to install the bar, if installing the bar in some other spot in the panel or even some other manufacturer's bar - you may need to remove paint behind the bar.

If you have a panel that contains the service disconnecting means and bonding screw installed in the grounded conductor bus, do you make jumpers from the grounded conductor bus to any EGC bars installed in the panel, or are they bonded via the cabinet? Most will say they are bonded via the cabinet and no additional jumpers are needed, if you install additional jumpers then the bonding screw shouldn't be needed, and is one way to do the bonding if you lost the screw.

I had this same question as the OP come up the other day and have had this question a number of times. I'm with you, I think a panel used as service equipment illustrates that no jumper would be required between ground bars just like you would not use one in a service rated panel. Another example that illustrates that the enclosure is an EGC is when you need to bond a conduit entry to an enclosure you can use a bonding bushing with a jumper to the enclosure and then continue the conduit out another KO with another bonding bushing and jumper. I think all of these types of examples clearly imply that a metallic enclosure is an approved EGC.

 

[mwm1752]

it appears that a screw could be considered a bonding jumper & all terminals are connected to the same metal surface - no bonding between terminals are required IMHO

250.28 Main Bonding Jumper and System Bonding Jumper. For a grounded system, main bonding jumpers and system bonding jumpers shall be installed as follows:
(C) Attachment. Main bonding jumpers and system bonding jumpers shall be connected in the manner specified by the applicable provisions of 250.8.
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:
(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

 

[jaggedben]

One could argue that a box or the case of a panelboard is a raceway, in which case if your box or panelboard is listed then you can use it as an EGC as long as you don't otherwise violate the listing instructions.

As for the fact that everyone sometimes uses metal boxes that aren't listed.... Yeah, that's one of those things everybody does even though there isn't a legalistic justification in the code.

 

[petersonra]

One could argue that a box or the case of a panelboard is a raceway, in which case if your box or panelboard is listed then you can use it as an EGC as long as you don't otherwise violate the listing instructions.

As for the fact that everyone sometimes uses metal boxes that aren't listed.... Yeah, that's one of those things everybody does even though there isn't a legalistic justification in the code.

where does it say in the code that metal boxes have to be listed?

 

[JJspark]

I talked to the inspector today about this. He said it is not UL listed to be an EGC.

 

[texie]

I talked to the inspector today about this. He said it is not UL listed to be an EGC.

Let's look at a garden variety service rated Panel. You put the neutral bond screw in. You install a factory ground bar because you want the extra terminals for equipment grounding conductors (that you could otherwise connect to the neutral bar in this case). Is he the then saying that you need a bonding jumper from the EGC bar to the neutral bar? How would this be any different than the case of multiple EGC bars?

 

[mwm1752]

I talked to the inspector today about this. He said it is not UL listed to be an EGC.

State Inspector?

 

[texie]

I talked to the inspector today about this. He said it is not UL listed to be an EGC.

As I ponder this further, the more absurd it is. Let's try another example. Let's say you have sub panel fed with a metallic raceway that qualifies as an EGC and you have no wire type EGC in the feeder. Then you add branch circuits that have a wire type EGC so you add a factory ground bar kit to land them on. It should be obvious that whether you have 1 or 4 ground bars with a jumper between them the enclosure will still have to carry the short circuit current back to the feeder conduit. I would ask this inspector would he require a bonding jumper if you only had 1 ground bar and if so where would you connect each end?

 

[infinity]

I talked to the inspector today about this. He said it is not UL listed to be an EGC.

Well he's incorrect, now is up to you to decide if you want to fight him on it by going over his head or just add the jumpers. What size jumpers did he say that you're "required" to use?

 

[kwired]

I talked to the inspector today about this. He said it is not UL listed to be an EGC.

He might be correct, only because it was never tested for that specific purpose, but no real need to if NEC recognizes it as being suitable to use as part of the EGC path.

 

[jaggedben]

where does it say in the code that metal boxes have to be listed?

250.118.

It doesn't have to be listed to use it as a box, but it has to be listed if you want to use it as an EGC. That is, if it's not one of the other items identified in that section.

 

[wwhitney]

There's a fundamental conflict between the definition of EGC, 250.118, and common practice:

(2017) Grounding Conductor, Equipment The conductive path(s) that provides a ground-fault current path and connects normally non-current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both.

(2017) 250.118 Types of Equipment Grounding Conductors. The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more of a combination of the following:

Now "metallic equipment enclosures" clearly "enclose circuit conductors" yet are not listed in 250.118. But common practice is to rely on metallic equipment enclosures as a component of the "ground-fault current path". Hence the conflict.

This could easily be resolved by adding "metallic equipment enclosures" to the list in 250.118. Right now everyone behaves as if that were the case.

Cheers, Wayne

 

[Ponchik]

I talked to the inspector today about this. He said it is not UL listed to be an EGC.

If the enclosure is not UL listed to be EGC then essentially what he requires is all of the metallic conduits to have a grounding bushings as they enter the enclosure.

 

[macmikeman]

250.96 (A) specifically mentions enclosures, which allows the practice .


I think this is merely a case of that inspector once read that the building steel is not to be used as a bonding path. A panel board is not '' building steel'', but of course many inspectors once countered with that will begin with the '' we interpret this to mean the panel boards are what this is referring to.....

 

[necGuru]

This could easily be resolved by adding "metallic equipment enclosures" to the list in 250.118. Right now everyone behaves as if that were the case.

Cheers, Wayne

I kind of agree with you. BTW - They don't use the term "metallic" anymore - now they will only use the term "metal." I'm going to try to add that like you say.

This debate has gone on for far too long and it should be made much clearer in the code one way or the other. I should point out that nobody here in this forum saw what the inspector saw. If the EC attempted to use a different ground bar (one that is not listed for that particular panel) :jawdropr if they didn't use the factory threads, of if they didn't use the correct machine screws, the inspector would be 100% correct in requiring the bonding jumper. So while it is easy to generalize, in all reality - we just don't know.

:thumbsup: Got to run, thanks.

 

[nickelec]

How many panels, cabinets have provisions for multiple egc bars? I have seen some with 2 different possible mounting locations, if you install an EGC bar say with self tappers anywhere wouldn't that voilate the ul listing of that can by not using it the way it was intended?

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