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Discussion Starter · #1 ·
In the 2017 Edition of the National Electric Code, (1) in (B) and (1) in (C) both in Section 250.32 specify, "An equipment grounding conductor, as described in 250.118, shall be run with the supply conductors and be connected to the building or structure disconnecting means and to the grounding electrode(s)." However, it does not specify whether they have to connect directly or indirectly. Furthermore, typically, the EGC is connected to the main bonding jumper (typically a neutral bus bar), which in turns connects to the GEC, which in turns connects to the grounding electrode(s). That means the EGC is indirectly connected to the grounding electrode(s). According to the standard practice of EGC installations, 250.32(B)(1) and 250.32(C)(1) allow indirect connections as much as direct connections.

250.130(A) also says that the EGC for grounded systems must be bonded to the GEC and system grounded conductor (neutral wire). Again, it does not specify whether of not the bonding has to be direct or indirect. Again, the standard EGC is bonded indirectly to both the GEC and system grounded conductor, because it first needs to go through the main bonding jumper. So, this effectively also allows indirect bonding as much as direct bonding.

So, is one allowed to connect an EGC directly to any GEC that connects to the main bonding jumper at the other end? This way, the EGC in indirectly connected with the disconnecting means, just like with the grounding electrode(s), GEC, and system grounded conductor. Furthermore, a GEC is electrically way better than a regular EGC because it has a way lower resistance and is tougher. That way, the section of the GEC between the EGC and main bonding jumper is not classified as an EGC for official purposes, just like the main bonding jumper, though they both in essence function as one.

For example, the GEC can be a standard structural metal frame of a building, which has practically zero resistance (practically infinitely higher current carrying capacity) compared to a normal wire, but does not qualify as an EGC under 250.118. That way, if one classifies in the plan for the frame as only a GEC, one can circumvent the requirement of 250.118 and the prohibition in 250.136(A) of the frame being used as an EGC, as well as save large amounts of money, if the equipment is directly connected to an EGC before being connected to a GEC on the way to the disconnecting means.
 

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So, your question is why the structural steel of a building can't be used for an EGC as prohibited by 250.136(A)

The structural metal frame of a building shall
not be used as the required equipment grounding conductor
for ac equipment.
The structural steel is bonded to the grounded service conductor to prevent it from becoming energized just like any other metallic system like plumbing might be. Structural steel is not intended to be a current carrying conductor in the event of a fault, it's only bonded to prevent it from becoming energized. It's often not a low resistance or low impedance path as you believe. In my experience I have found large voltage differences between building steel and the EGC of a receptacle, so much so that it destroyed the equipment that was plugged into the receptacle and also required to be grounded to the building steel. Likely that voltage difference was cause by the voltage drop on the neutral someplace between the receptacle, subpanel(s) and service where the steel was bonded.

-Hal
 

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Discussion Starter · #4 ·
So, your question is why the structural steel of a building can't be used for an EGC as prohibited by 250.136(A)



The structural steel is bonded to the grounded service conductor to prevent it from becoming energized just like any other metallic system like plumbing might be. Structural steel is not intended to be a current carrying conductor in the event of a fault, it's only bonded to prevent it from becoming energized. It's often not a low resistance or low impedance path as you believe. In my experience I have found large voltage differences between building steel and the EGC of a receptacle, so much so that it destroyed the equipment that was plugged into the receptacle and also required to be grounded to the building steel. Likely that voltage difference was cause by the voltage drop on the neutral someplace between the receptacle, subpanel(s) and service where the steel was bonded.

-Hal
Are you kidding me!? I do not believe that a building frame would be possible to not have a low impedance. That is because the building frame has a huge mass and its members have a huge combined cross-sectional area in any plane, which is at least 10,000 times greater than that of a large copper wire. Assuming that structural steel has an impedance per unit mass of cross-sectional area of 1/10 of that of a copper wire (reasonable estimate), it still has as little as 1/1000 of the total impedance. If the impedance per unit is 1/20, then the total impedance is 1/500.
 

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Discussion Starter · #5 ·
Also, if the building frame were not low impedance, then why would 250.68(C)(2) explicitly allow it to be used as a grounding electrode conductor, which has even higher current-carrying capacity requirements compared to an equipment grounding conductor?
 

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Discussion Starter · #6 ·
Also, if structural metal were not low impedance, then why would vehicles be using them in essence (and probably officially too) as not only the equipment grounding conductor, but also the system grounding conductor? Yes, I know that vehicles, except RVs that have their interior circuits directly connected to the grid, are not covered by the NEC. However, land vehicles, non-fibreglass watercraft, and aircraft still wouldn't be using the body shell as both the ground and neutral, due to practical reasons of energy efficiency, if it were not low impedance.
 

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Discussion Starter · #7 ·
So, your question is why the structural steel of a building can't be used for an EGC as prohibited by 250.136(A)
Except that is not my question here. My question is about whether or not one can connect an EGC directly to a GEC in general, not just building frames, and in essence use the GEC as the required path for an EGC (and not even necessarily as an EGC per se) without counting it as a GEC in any legal manner.
 

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Are you kidding me!? I do not believe that a building frame would be possible to not have a low impedance.
Well, since you are so smart why don't you submit a proposal to the NEC and see if you can't get it changed?

Except that is not my question here. My question is about whether or not one can connect an EGC directly to a GEC in general, not just building frames, and in essence use the GEC as an EGC without counting it as a GEC in any legal documentation.
So, you want to use the neutral for an EGC? A first year apprentice knows the answer to that! Are you even in the trade??

-Hal
 

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Discussion Starter · #9 ·
So, you want to use the neutral for an EGC? A first year apprentice knows the answer to that! Are you even in the trade??

-Hal
Nope, I definitely do not want to use the neutral for an EGC. That is because the neutral wire has a non-insignificant impedance, and the NEC allows up to a 3% voltage drop. 3% of 240V is 7.2V, which is substantial. What I'm wanting is to use the structural components as both an EGC and neutral conductor. That is because the imepedance of the structural components is so low (as evidenced in cars, buses, trains, airplanes, ferries, and cruise ships) that the voltage drop is too low to be measured, so even ground loops for Hi-Fi equipment are practically nonexistent.
 

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Discussion Starter · #12 ·
I'm asking about the exact intent of the NEC by its creator (NFPA) or buildings department, and I thought there would be some people here that are part of those administrative boards. So, that is why I asked. If it is only electricians who are not part of permit-approving boards here, then of course it is pointless to ask here. However, one first needs to try on order to know. That is why I'm posting here to see if I can try to get any insider information from the authors of the NEC and electrical permit issuers.

So, is it normally only electricians here, or are there also a substantial amount of posts from NFPA staff and electrical permit issuers here?
 

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I'm asking about the exact intent of the NEC by its creator (NFPA) or buildings department, and I thought there would be some people here that are part of those administrative boards. So, that is why I asked. If it is only electricians who are not part of permit-approving boards here, then of course it is pointless to ask here. However, one first needs to try on order to know. That is why I'm posting here to see if I can try to get any insider information from the authors of the NEC and electrical permit issuers.

So, is it normally only electricians here, or are there also a substantial amount of posts from NFPA staff and electrical permit issuers here?
to my knowledge there are no people here who are affiliated or associated with NFPA or NEC in any manner
 

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I'm asking about the exact intent of the NEC by its creator (NFPA)
I know you asked this over at Holt's. I don't remember if it is Dennis (moderator here also) but there are a couple of guys who interact with the Code making panels. I can tell you that it's been that way so long there may not be any history on it.

I can also tell you that if you are going to be a know-it-all and contradict whatever we tell you, you'll get the boot...

-Hal
 

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Worked for years in a juice plant that's covered in stainless pipes and structural steel. Replaced motors, conduit, wire and 2 control panels that were completely destroyed by welders forgetting to move there ground clamps.
 

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Discussion Starter · #20 · (Edited)
Worked for years in a juice plant that's covered in stainless pipes and structural steel. Replaced motors, conduit, wire and 2 control panels that were completely destroyed by welders forgetting to move there ground clamps.
But this is only in practice though just because there are enough careless people that made this event not rare enough to not be a problem, as evidenced by you encountering this event, unless you were so lucky/unlucky to just happen to be the only person in the world to replace the equipment in this type of cause of failure. I do not have enough statistics, so I cannot comment on the rarity of the event. In principle, there is no risk at all if no one ever makes a relevant mistake. That is evidenced by pilots of most airlines and train drivers in Japan, where no pilot/driver ever makes a critical mistake outside of freak events.
 
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