Sizing a bonding screw

jim dungar said:
Manufacturers that get their equipment Listed do not need to follow NEC.
You can drive yourself crazy trying to figure out why manufactures can do stuff you can't.
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I thought all electrical installations were governed (at least in the USA and a few other international countries that have adopted it) by the NEC. Article 110.3 says even if you get it tested and listed, it’s still under the guidelines of the good old NEC.
 
Light Sabre said:
I thought all electrical installations were governed (at least in the USA and a few other international countries that have adopted it) by the NEC. Article 110.3 says even if you get it tested and listed, it’s still under the guidelines of the good old NEC.
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The requirements used to get the product listed do not need to comply with the NEC they only need to comply with the requirements of the listing which may or may not be the same as the NEC.
 
infinity said:
The requirements used to get the product listed do not need to comply with the NEC they only need to comply with the requirements of the listing which may or may not be the same as the NEC.
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The back and forth hurts my brain… but are you saying that the bond screw shipped with the listed assembly has been tested to be ok to be the main bonding jumper, and the GEC’s in these type of listed enclosures are allowed to terminate to the EGC bus without the use of a wire or busbar connection?
 
Light Sabre said:
The back and forth hurts my brain… but are you saying that the bond screw shipped with the listed assembly has been tested to be ok to be the main bonding jumper, and the GEC’s in these type of listed enclosures are allowed to terminate to the EGC bus without the use of a wire or busbar connection?
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No I'm not saying that. In fact I mentioned just the opposite several times already in this thread. The bonding screw shipped with the panel is adequate only as the MBJ.
 
Ok! That’s what I was thinking… it just gets confusing sometimes when it seems like “the assembly” that has a screw shipped with it is somehow “listed” for the purpose of taking the place of the wire or busbar connection. At least this is what a lot of people’s interpretation is, and I’m just trying to clear up my own interpretation. Thanks for your help!!!
 
I will always look for a wire or busbar connection between the GC bar and the EGC bar if the GEC’s are going to the EGC bus… it is a code violation otherwise
 
Light Sabre said:
I thought all electrical installations were governed (at least in the USA and a few other international countries that have adopted it) by the NEC. Article 110.3 says even if you get it tested and listed, it’s still under the guidelines of the good old NEC.
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Yes, the installation of the Listed equipment is subject to NEC requirements.
But the internal parts of the equipment are subject to the Listing requirements.
 
Light Sabre said:
I will always look for a wire or busbar connection between the GC bar and the EGC bar if the GEC’s are going to the EGC bus… it is a code violation otherwise
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From an inspection perspective I would start with where is the GEC landed if on the neutral then the MBJ can be a screw. If the GEC is landed on the EGC bus then MBJ cannot be a screw.
 
Just to help my interpretation a bit more… Is it a fair statement to say that bonding screws are really only meant to be used for bonding equipment grounding conductors?
 
Light Sabre said:
Just to help my interpretation a bit more… Is it a fair statement to say that bonding screws are really only meant to be used for bonding equipment grounding conductors?
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The Article 100 definition sums it up nicely.

Bonding Jumper, Main.
The connection between the grounded circuit conductor and the equipment grounding conductor, or the supply-side bonding jumper, or both, at the service.
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infinity said:
The NEC doesn't tell you what size the screw used as a MBJ must be. It's likely part of the UL listing where it must be tested using certain parameters. The screw that comes with the panel is adequate as the MBJ. It is not adequate to allow the GEC to be connected to the EGC bus.
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it will make you crazy trying to figure out how these kinds of things are determined. UL has actually tested them under short circuit conditions and they work as needed.
 
I think It makes pretty good sense to me… The screw has probably been tested for the highest fault it can take based from the size of the how big of a main breaker the panel it’s listed with is rated for. Correct me, but I believe the intent of testing the screw is meant for a fault within the system in a building/ structure that the listed assembly is serving. The electrodes are where we are trying to dissipate the excess current into the earth when a fault occurs (Or a possible lightning strike… bummer)… In the event of a fault current, whatever available power coming from the transformer (let’s say 50kva) has just found a path that we do not want it to take. If the electrodes do not have a large enough, low resistance path that we install by using a wire or busbar, and only rely on a screw, then bad things can happen. We need to make sure to try and dissipate the fault into the earth as fast as possible. The connection is intended by 250.24(A)(4) to either make a direct connection to the grounded conductor with the electrodes, or if you need to take the electrodes to the equipment ground’s busbar, then a more robust connection than just the screw it is listed with, to get that fault dissipated, such as a wire or busbar… right?
 
Light Sabre said:
… right?
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Sorry, wrong. Earth has nothing to do with it, other than lightning.

The real purpose of the EGC system is so that a fault from an energized line to a normally-grounded (non-energized) surface mimics a fault from an energized line to the neutral (which happens to be earthed).
 
LarryFine said:
Sorry, wrong. Earth has nothing to do with it, other than lightning.

The real purpose of the EGC system is so that a fault from an energized line to a normally-grounded (non-energized) surface mimics a fault from an energized line to the neutral (which happens to be
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So, then what’s the difference where the electrode goes? Is there a difference from a neutral fault or a ground fault if they are mimicking each other?… the fault can occur on either. Then why the wire or busbar connection, when the grounding conductors aren’t required to terminate directly to the grounded conductor? The equipment grounding conductors are allowed to go to either by using anything in 250.28, and yet the electrodes are not allowed. Why is this?
 
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