NEC 250.134 (A) with respect to bonding enclosures w/ bolt

[phebejtsov]

Does the handbook allow for bonding bonding separate enclosures with bolt? In summary, can two enclosures standing side-by-side be bonded w/ a bolt threading through both panel enclosures?

Looking all over the handbook & the closet section I've found to is in 250.134(A). "Equipment Fastened in Place or
Connected by Permanent Wiring Methods"

However, it refers to 250.118, which states that only busbars, rigid conduits & metal raceways area allow to to be consider grounding paths.

Any suggestions? Thanks

 

[Little Bill]

Does the handbook allow for bonding bonding separate enclosures with bolt? In summary, can two enclosures standing side-by-side be bonded w/ a bolt threading through both panel enclosures?

Looking all over the handbook & the closet section I've found to is in 250.134(A). "Equipment Fastened in Place or
Connected by Permanent Wiring Methods"

However, it refers to 250.118, which states that only busbars, rigid conduits & metal raceways area allow to to be consider grounding paths.

Any suggestions? Thanks

Assuming one of the enclosures is properly grounded & bonded, 250.96(A) might be what you are looking for.

 

[ActionDave]

I would say no, but you could use a RMC nipple or the like.

 

[don_resqcapt19]

Both 250.110 and 250.134 require a connection from an EGC to the enclosure. A bolt is not an EGC and using it as one would be a code violation.

 

[Twoskinsoneman]

Both 250.110 and 250.134 require a connection from an EGC to the enclosure. A bolt is not an EGC and using it as one would be a code violation.

I understand this may not be popular but I disagree with this statement. A don't see anything that says a bolt cannot be an EGC.
First of all 250.118 specifically describes what types of EGCs have to be run with the circuit conductors... to me there is a distinction between EGCs that have to run with circuit conductors and EGCs that can be used to connect other non-current carrying metal parts.

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

Look at this example: other metal non-current-carrying parts that can serve as EGC?

250.96 Bonding Other Enclosures.
(A) General. Metal raceways, cable trays, cable armor,
cable sheath, enclosures, frames, fittings, and other metal
non?current-carrying parts that are to serve as equipment
grounding conductors,

Look at this example: equipment is considered grounded if "secured" to a structure that is connected to an EGC?
Very likely this equipment is being grounded by bolts, or screws.

250.136 Equipment Considered Grounded. Under the
conditions specified in 250.136(A) and (B), the normally
non?current-carrying metal parts of the equipment shall be
considered grounded.
(A) Equipment Secured to Grounded Metal Supports.
Electrical equipment secured to and in electrical contact
with a metal rack or structure provided for its support and
connected to an equipment grounding conductor by one of
the means indicated in 250.134. The structural metal frame
of a building shall not be used as the required equipment
grounding conductor for ac equipment.

Here the code allows a strap to be used to ground equipment:
(Something else not listed in 250.118)

250.138 Cord-and-Plug-Connected Equipment. Non?
current-carrying metal parts of cord-and-plug-connected
equipment, if grounded, shall be connected to an equipment
grounding conductor by one of the methods in 250.138(A)
or (B).
(A) By Means of an Equipment Grounding Conductor.
By means of an equipment grounding conductor run with
the power supply conductors in a cable assembly or flexible
cord properly terminated in a grounding-type attachment
plug with one fixed grounding contact.
Exception: The grounding contacting pole of groundingtype
plug-in ground-fault circuit interrupters shall be permitted
to be of the movable, self-restoring type on circuits
operating at not over 150 volts between any two conductors
or over 150 volts between any conductor and ground.
(B) By Means of a Separate Flexible Wire or Strap. By
means of a separate flexible wire or strap, insulated or bare,
connected to an equipment grounding conductor, and protected
as well as practicable against physical damage,
where part of equipment.

Anyway this may be considered semantics I know but not allowing a bolt (which I believe would create a fine low-impedance path) because it does not specifically say "bolt" in 250.118 is short-sighted.

 

[Little Bill]

Both 250.110 and 250.134 require a connection from an EGC to the enclosure. A bolt is not an EGC and using it as one would be a code violation.

I didn't read the OP as asking about the EGC. He asked about bonding the two panels.

 

[jumper]

Nice post Twoskinsoneman. Good detail for your argument.:thumbsup::thumbsup::thumbsup:

 

[Little Bill]

I understand this may not be popular but I disagree with this statement. A don't see anything that says a bolt cannot be an EGC.
First of all 250.118 specifically describes what types of EGCs have to be run with the circuit conductors... to me there is a distinction between EGCs that have to run with circuit conductors and EGCs that can be used to connect other non-current carrying metal parts.



Look at this example: other metal non-current-carrying parts that can serve as EGC?

Originally Posted by NEC

250.96 Bonding Other Enclosures.
(A) General. Metal raceways, cable trays, cable armor,
cable sheath, enclosures, frames, fittings, and other metal
non?current-carrying parts that are to serve as equipment
grounding conductors,

Anyway this may be considered semantics I know but not allowing a bolt (which I believe would create a fine low-impedance path) because it does not specifically say "bolt" in 250.118 is short-sighted.

That is why I told the OP to look at 250.96 in my first post.

 

[renosteinke]

You've hit on one of the weaknesses in the 'rules,' as it were. Let's look at a couple twists on the situation ....

In the first 'twist,' imagine a panel with a second ground bar added. Is there any requirement or need to connect the two ground bars with a wire, or is the sheet metal of the panel case sufficient? Personally, I don't see any code rule that requires a wire, but I use one anyway- usually a #12 to match the circuits using the bar.

In the second 'twist,' imagine that one of your two panels is the 'main' panel. Do you separate the neutral from the ground at the adjoining panel? I spent one Thanksgiving troubleshooting a building that had suffered severe voltage fluctuations; the cause turned out to be that the 21-yr. old lock nuts connecting the two panels had come loose. Those lock nuts were, in essence, acting as the neutral wire between the two panels. (Inspecting is a funny art; I noticed the use of a green screw on the neutral buss before I noticed that there was no neutral wire between the panels!)

I've encountered a few assemblies where the 4-square boxes were bolted together as you describe. Doing so always results in the two box covers / mud rings interfering with each other. There's also the fine point of one of the boxes having a 'sharp' screw tip sticking into it.

Would the use of such a bolt allow you to eliminate a bonding jumper to one of the boxes? I don't think so. Code language requires such a jumper according to the circumstances of each box, without regard to what other boxes may be in the run, or how they're all tied together.

 

[don_resqcapt19]

...Anyway this may be considered semantics I know but not allowing a bolt (which I believe would create a fine low-impedance path) because it does not specifically say "bolt" in 250.118 is short-sighted.

An EGC is required to be run with the circuit conductors to the equipment in question. 300.3(B)
I don't see how I can use a bolt as the EGC for the equipment as there is no way to run it (the bolt) with the circuit conductors.

 

[phebejtsov]

250.28 Main Bonding Jumper and System Bonding Jumper, Section A & B

250.28 Main Bonding Jumper and System Bonding Jumper, Section A & B

Great discussion. I believe I've stumbled on to the answer, in conjunction with 250.96 as stated earlier, 250.28 indicates the use copper or corrosive-resistive screw w/ green finish identifier.

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:
(A) Material. Main bonding jumpers and system bonding
jumpers shall be of copper or other corrosion-resistant material.
A main bonding jumper and a system bonding jumper
shall be a wire, bus, screw, or similar suitable conductor.
(B) Construction. Where a main bonding jumper or a system
bonding jumper is a screw only, the screw shall be identified
with a green finish that shall be visible with the screw
installed.

 

[don_resqcapt19]

Great discussion. I believe I've stumbled on to the answer, in conjunction with 250.96 as stated earlier, 250.28 indicates the use copper or corrosive-resistive screw w/ green finish identifier.

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:
(A) Material. Main bonding jumpers and system bonding
jumpers shall be of copper or other corrosion-resistant material.
A main bonding jumper and a system bonding jumper
shall be a wire, bus, screw, or similar suitable conductor.
(B) Construction. Where a main bonding jumper or a system
bonding jumper is a screw only, the screw shall be identified
with a green finish that shall be visible with the screw
installed.

I don't see how a rule for the main or system bonding jumper applies to a question about the equipment grounding conductor.

 

[Little Bill]

I don't see how a rule for the main or system bonding jumper applies to a question about the equipment grounding conductor.

Don, the way I read the OP is, he is asking about "bonding" the two enclosures together, not about an EGC. As I stated earlier, this depends on if he has properly grounded/bonded one of the panels, meaning EGC ran already.

 

[don_resqcapt19]

Don, the way I read the OP is, he is asking about "bonding" the two enclosures together, not about an EGC. As I stated earlier, this depends on if he has properly grounded/bonded one of the panels, meaning EGC ran already.

If both of the enclosures have an EGC connection, I would not see an issue. If only one does, then the bolt is being used as the EGC for the second panel and I see no provision in the code to permit that.

 

[Little Bill]

If both of the enclosures have an EGC connection, I would not see an issue. If only one does, then the bolt is being used as the EGC for the second panel and I see no provision in the code to permit that.

With the absence of the OP, we could speculate forever. I suppose to answer his situation correctly, we need more info from him. I will add this, if the OP had two separate panels, both with an EGC, I would see no need to bond the two enclosures together.

 

[petersonra]

This can be argued forever. there is nothing in the code that says you can use an enclosure as part of your EGC either but it is done routinely.

 

[Twoskinsoneman]

I will admit it gets a little fuzzy for me.
Why can't the bolt between the two panels be a equipment bonding jumper?

 

[Twoskinsoneman]

I guess what I meant by fuzzy is I feel like the grounding/bonding section in the NEC is grown way too complicated and convoluted.

Here's an example.

This Section states receptacles need an equipment bonding jumper on the grounding terminal.

250.146 Connecting Receptacle Grounding Terminal to
Box. An equipment bonding jumper shall be used to connect
the grounding terminal of a grounding-type receptacle
to a grounded box unless grounded as in 250.146(A)
through (D).

This section states if a receptacle has an EGC terminal it has to be connected to EGC

404.6(B) To Be Grounded. Receptacles and cord connectors
that have equipment grounding conductor contacts shall
have those contacts connected to an equipment grounding
conductor.

Are equipment bonding jumpers and EGCs the same?
250.102 says equipment bonding jumpers can be a screw or anything suitable.

When things aren't exactly clear I would defer to common sense. Any inspector that wants a wire run from one panel to another when the two are bolted together may be too caught up in the technicalities to remember what we are trying to accomplish. He probably wouldn't be happy even if they were welded together. So I'll run the wire and take out on my dog when I get home!

 

[elohr46]

I look at it this way; If they don't allow the "grounded conductor" to be connected via metal enclosure(art.200.2(B) 2008NEC) then they shouldn't allow the "grounding conductor" to be either. They both are responsible for carrying fault currents.

 

[phebejtsov]

Clarification

Clarification

Don, the way I read the OP is, he is asking about "bonding" the two enclosures together, not about an EGC. As I stated earlier, this depends on if he has properly grounded/bonded one of the panels, meaning EGC ran already.

Little Bill, you've hit it on the spot. To clarify the original post:

I'm envisioning a series of free-standing enclosures bolted side by side with at least one of the enclosure having a EGC. Instead of drilling additional holes to pass a EGC through each panels, suffice to say will the bolts pass a bonding element?

I interpret the NEC guidelines that it does.