Bonding Grounding Electrode Conductor to Transformer

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GrummanWildcat

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To provide temporary construction power, the contractor chose to terminate the Grounding Electrode Conductor from building steel to a bolted lug on the outside of a dry transformer case which is through-bolted to a neutral lug on the inside of the case. Both lugs connect to a common bolt separated by the sheet metal housing.

The transformer is a delta/wye 480/120-208 and mounted on a mobile skid with secondary panel attached to the side of the transformer housing. Primary power feeds into a safety switch mounted on the opposite side of housing as the panel. Secondary panel feeds power cords to spider boxes and other job site temporary power.

The question I ponder is if the GEC termination on the outside of the transformer meets the intent of NEC 250.30. NEC Handbook provides two illustrations depicting the GEC terminating at a common lug or buss inside either the transformer or the secondary panel. I would prefer the illustrated scenario with a common lug. However, my job is to determine if the existing by the contractor meets code.

Another variation to consider: If the exterior GEC lug was bolted to the neutral lug inside the transformer, does that change the outcome?
 
GrummanWildcat said:
To provide temporary construction power, the contractor chose to terminate the Grounding Electrode Conductor from building steel to a bolted lug on the outside of a dry transformer case which is through-bolted to a neutral lug on the inside of the case. Both lugs connect to a common bolt separated by the sheet metal housing.

The transformer is a delta/wye 480/120-208 and mounted on a mobile skid with secondary panel attached to the side of the transformer housing. Primary power feeds into a safety switch mounted on the opposite side of housing as the panel. Secondary panel feeds power cords to spider boxes and other job site temporary power.

The question I ponder is if the GEC termination on the outside of the transformer meets the intent of NEC 250.30. NEC Handbook provides two illustrations depicting the GEC terminating at a common lug or buss inside either the transformer or the secondary panel. I would prefer the illustrated scenario with a common lug. However, my job is to determine if the existing by the contractor meets code.

Another variation to consider: If the exterior GEC lug was bolted to the neutral lug inside the transformer, does that change the outcome?
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Not exactly the way I would prefer it be done either, but I believe it does meet code.

First, what you are calling a neutral lug is more likely one end of the System Bonding Jumper. It would only be a neutral if it were connected in such a manner as to be a current carrying conductor (CCC), and being connected to the enclosure I will assume it is not a CCC. The other end of the conductor in this lug is likely connected to the X0 terminal, or by some other approved means, to a neutral conductor connected to X0.

This meets the code that I find applicable:
Regarding GEC connection, 250.30(A)(3) "... This connection shall be made at the same point on the separately derived system where the system bonding jumper is connected." Note there is no explicit requirement as to which end of the system bonding jumper (SBJ).

Regarding SBJ connection, 250.28(C) Attachment. Main bonding jumpers and system bonding jumpers shall be connected in the manner specified by the applicable provisions of 250.8

Under 250.8(A)(5), "Machine screw-type fasteners that engage not less thantwo threads or are secured with a nut" would apply.​

Not sure what to make of your variation. The way I read it, it is the same as the existing, Do you perhaps mean if the GEC and its lug were placed on the inside... using same bolt, nut, SBJ and its lug and hole thru enclosure?
 
maybe I'm missing something - I don't see a violation. doesn't this need to connect to all the required electrodes as required, though ? (not just building steel) (590.2 A, 590.4A)
 
nakulak said:
doesn't this need to connect to all the required electrodes as required, though ? (not just building steel)
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Yes... but only if they exist. In the case in new construction, they often don't exist at the time the temp power is set up. The OP does not elaborate on whether any of the other electrodes exist.
 
The connection is a violation. Both the grounding electrode conductor and the system bonding jumper must be connected to the grounded conductor at the same point. We do not have that in this installation. If the system bonding jumper is installed in the transformer, then both the GEC and the system bonding jumper must be connected to XO in the transformer.
 
Smart $ said:
Reference please?
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The same one that you cited. The GEC is required to connect directly to the grounded conductor. That did not happen in this installation. Also the bolt is being used as the GEC and that is not a permitted material for use as a GEC and it is a splice in the GEC that is not permitted.
 
don_resqcapt19 said:
The same one that you cited. The GEC is required to connect directly to the grounded conductor. That did not happen in this installation.
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I always do it that way myself... but for some unbeknownst reason I could not find it in the code... even though it was right under my nose :mad:

Embedded in the first sentance of 250.30(A)(3) is "...shall be used to connect the grounded conductor of the derived system to the grounding electrode..."

Yet if you were to follow this to a tee (i.e. to be technically correct), you cannot connect the GEC to X0, because it is a terminal, and not a busbar, and not the grounded conductor !!!

don_resqcapt19 said:
Also the bolt is being used as the GEC and that is not a permitted material for use as a GEC and it is a splice in the GEC that is not permitted.
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That is correct. Reference 250.64(C).
 
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Smart $ said:
I always do it that way myself... but for some unbeknownst reason I could not find it in the code... even though it was right under my nose :mad:

Embedded in the first sentance of 250.30(A)(3) is "...shall be used to connect the grounded conductor of the derived system to the grounding electrode..."

Yet if you were to follow this to a tee (i.e. to be technically correct), you cannot connect the GEC to X0, because it is a terminal, and not a busbar, and not the grounded conductor !!!


That is correct. Reference 250.64(C).
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Exception No. 1: Where the system bonding jumper specified in 250.30(A)(1) is a wire or busbar, it shall be permitted to connect the grounding electrode conductor to the equipment grounding terminal, bar, or bus, provided the equipment grounding terminal, bar, or bus is of suffıcient size for the separately derived system.

​
 
weressl said:
Exception No. 1: Where the system bonding jumper specified in 250.30(A)(1) is a wire or busbar, it shall be permitted to connect the grounding electrode conductor to the equipment grounding terminal, bar, or bus, provided the equipment grounding terminal, bar, or bus is of suffıcient size for the separately derived system.

​
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Not so :mad: now, but still disappointed in myself for not being able to counterpoint on my own :D
 
Laszlo,
Are you saying the exception makes this installation legal? I don't see it that way. The bolt is not the "equipment grounding terminal bar or bus".
 
don_resqcapt19 said:
Laszlo,
Are you saying the exception makes this installation legal? I don't see it that way. The bolt is not the "equipment grounding terminal bar or bus".
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First, your quote is not an accurate quote. It should be "...equipment grounding terminal, bar, or bus, ..." The commas clearly separate three possible termination types.

From there, please cite reference(s) which prohibits or otherwise discredits the bolt as an "equipment grounding terminal" (other than it not have a green nut under 250.126(2); "Quick, someone paint that nut." :rolleyes:).

Aside from that, I've never known a bolt to actually be considered the terminal by itself. It is usually the surface to which a conductor is terminated that is the terminal. The bolt is simply part of the connection. A lot of terminal lugs wouldn't be much good without fasteners. ;)
 
I would red tag it. I don't see a bolt as meeting the intent of the code section. Also unless the EGC(s) are also connected to the same terminal (bolt) point, the conductor is not a "system bonding jumper" and the exception would not apply.
 
Smart $ said:
...Aside from that, I've never known a bolt to actually be considered the terminal by itself. It is usually the surface to which a conductor is terminated that is the terminal. The bolt is simply part of the connection. A lot of terminal lugs wouldn't be much good without fasteners. ;)
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Yes, you may need a bolt and a nut to connect a terminal, but that really makes my point that the bolt is not the terminal. I wouldn't even say that the surface is the terminal...the terminal is the device that connects the conductor to the surface. Where a conductor is directly connected to the surface, there is no terminal.
 
don_resqcapt19 said:
Yes, you may need a bolt and a nut to connect a terminal, but that really makes my point that the bolt is not the terminal. I wouldn't even say that the surface is the terminal...the terminal is the device that connects the conductor to the surface. Where a conductor is directly connected to the surface, there is no terminal.
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It seems there is conflicting points of view as to what actually constitutes a terminal :rolleyes:

There is no concise NEC definition.

Webster's Online Dictionary was no help.

Webster's Revised Unabridged Dictionary (1913) has this as one of 4 definitions:
Terminal
(n.)
Either of the ends of the conducting circuit of an electrical apparatus, as an inductorium, dynamo, or electric motor, usually provided with binding screws for the attachment of wires by which a current may be conveyed into or from the machine; a pole.
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This supports my opinion that a terminal is more a part of the equipment than it is the conductor.

110.14(A) also seems to support this conclusion at the start, "Connection of conductors to terminal parts..."

110.14(C)(2) also seems to support this conclusion, by calling conductor terminals separately installed pressure connectors.

...and out of all the transformers I've worked in, I recall only a extermely low percentage as actually having a designated equipment grounding terminal, bar, or bus.
 
don_resqcapt19 said:
Laszlo,
Are you saying the exception makes this installation legal? I don't see it that way. The bolt is not the "equipment grounding terminal bar or bus".
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Yes Don, (if) it is identified and marked so on the equipment, in the installation drawings and other documentation. A throughbolt that has threaded extensions on both the inside and outside of an electrical equipment and is often welded to the wall is a common way to provide equipment grounding terminal.
 
don_resqcapt19 said:
I would red tag it. I don't see a bolt as meeting the intent of the code section. Also unless the EGC(s) are also connected to the same terminal (bolt) point, the conductor is not a "system bonding jumper" and the exception would not apply.
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As I picture the OP situation, there are no wire-type EGC's within the transformer enclosure.

One of the problems with the Code is it only infers that a metal enclosure can be an EGC. For instance, you have a panelboard with all appropriate connections as designed. No wire-type EGC's are run with the circuit conductors, utilizing the metal conduit as the EGC. When the conduit is not required to be bonded, how can the panelboard enclosure not be an EGC?
 
weressl said:
Yes Don, (if) it is identified and marked so on the equipment, in the installation drawings and other documentation. A throughbolt that has threaded extensions on both the inside and outside of an electrical equipment and is often welded to the wall is a common way to provide equipment grounding terminal.
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I have never seen such a bolt on a dry transformer. Even if that is the case, unless the system bonding jumper and the EGC(s) are connected to the inside part of the bolt, it is still an violation.
 
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