Service raceway bonding- 250.92 & fittings for large conduits

[greenspark1]

Hi all, our typical service is a few sets of 4"C so they are run into the service panel via punched openings. They're often in rigid conduit, and use a compression fitting to secure them to the main panel/switchboard. I have read 250.92 (B) several times and can't understand if a 'regular' compression fitting is acceptable or needs additional bonding. (B)(3) seems to mean that they ARE acceptable since we make them up tight.
Does the threaded part of the fitting with a regular locknut provide enough bonding?
I've read the handbook commentary, EC&M article, etc but it seems unclear for this application/example. Thank you!

 

[infinity]

Like an EMT connector those fittings would require bonding beyond the standard locknuts for a metal raceway that contains service conductors. Many guys use bonding locknuts although some say they're not listed for use with connectors. You could use a bonding bushing.

 

[letgomywago]

Like an EMT connector those fittings would require bonding beyond the standard locknuts for a metal raceway that contains service conductors. Many guys use bonding locknuts although some say they're not listed for use with connectors. You could use a bonding bushing.

I've always used bonding bushings on these never the locknuts since they do a poor job imo. They make split bonding bushings too if these are already installed

 

[LarryFine]

They make split bonding bushings too if these are already installed

I have use a grounding or bonding wedge that is a ring with a gap that can be installed around the wires and clamped down by the lock-nut, then it gets a lug and a wire.

 

[greenspark1]

Thanks! Yes 2-part bonding bushings are handy. Any other comments are welcome.
We're confused by (B)(3) which seems to explicitly ALLOW these for bonding the service raceway "threadless couplings and connectors if made up tight for metal raceways and metal-clad cables". (2024 NEC)
How are we mis-reading/understanding this?
FWIW I've never seen other contractors use any sort of bonding wedge/locknut on the service.

 

[LarryFine]

FWIW I've never seen other contractors use any sort of bonding wedge/locknut on the service.

It was when an inspector required it in an existing commercial service. It merely jumped from the incoming service conduit to the trough with less than a foot of wire.

 

[infinity]

We're confused by (B)(3) which seems to explicitly ALLOW these for bonding the service raceway "threadless couplings and connectors if made up tight for metal raceways and metal-clad cables"

It's confusing because the first part of 250.92(B) says that standard locknuts cannot be used. The standard locknut even with a threadless connector can only be used for the mechanical connection.

250.(B) Method of Bonding at the Service
Bonding jumpers meeting the requirements of this article shall be used around impaired connections, such as reducing washers or oversized, concentric, or eccentric knockouts. Standard locknuts or bushings shall not be the only means for the bonding required by this section but
shall be permitted to be installed to make a mechanical connection of the raceway(s). Electrical continuity at service equipment, service raceways, and service conductor enclosures shall be ensured by one or more of the following methods:
1. Bonding equipment to the grounded service conductor by an applicable method in
250.8(A)
2. Connections made up wrenchtight using threaded couplings, threaded entries, or listed
threaded hubs on enclosures
3. Threadless couplings and connectors if made up tight for metal raceways and metal-clad
cables
4. Other listed devices, such as bonding-type locknuts, bushings, or bushings with bonding
jumpers

 

[wwhitney]

It's confusing because the first part of 250.92(B) says that standard locknuts cannot be used. The standard locknut even with a threadless connector can only be used for the mechanical connection.

The bolded sentence doesn't say that standard locknuts can't be part of a compliant bonding path, just that (two) standard locknuts shall not be the only means of bonding. A threadless connector is a listed fitting that uses a locknut as part of the fitting; it does not consist of "only" standard locknuts.

A threadless rigid connector is listed to UL Standard 514B "Conduit, Tubing, and Cable Fittings," while a bonding bushing or locknut is also listed to UL 467 "Grounding and Bonding Equipment." Both standards require what UL 514B calls a "current test" and UL 467 calls a "short-time current test." Up through conductor size 3/0 Cu and trade size 4", the test requirements of the two standards are identical, as far as what current is required to be withstood for what time period. (For 4" that's 5050A for 9 seconds). UL 467 has higher requirements for equipment intended for use with conductors larger than 3/0 Cu, while UL 514B's requirements do not increase for sizes beyond 3/0 Cu.

So it seems to me that a threadless connector, in conjunction with the provided locknut, does meet the requirements 250.5(B)(3), and is not prohibited for 250.5(B) bonding by the clause that excludes "standard locknuts" as the "only means" of bonding. Moreover, in terms of actual test performance, up through trade size 4", a bonding bushing listed to UL 467 has not been tested to a higher standard than a threadless rigid connector has been.

Cheers, Wayne

 

[david]

Hi all, they are run into the service panel via punched openings.

So you are using a knock out punch? So there would be nothing compromising the connection?

 

[greenspark1]

So you are using a knock out punch? So there would be nothing compromising the connection?

That's correct, no compromised connection.

 

[greenspark1]

The bolded sentence doesn't say that standard locknuts can't be part of a compliant bonding path, just that (two) standard locknuts shall not be the only means of bonding. A threadless connector is a listed fitting that uses a locknut as part of the fitting; it does not consist of "only" standard locknuts.

A threadless rigid connector is listed to UL Standard 514B "Conduit, Tubing, and Cable Fittings," while a bonding bushing or locknut is also listed to UL 467 "Grounding and Bonding Equipment." Both standards require what UL 514B calls a "current test" and UL 467 calls a "short-time current test." Up through conductor size 3/0 Cu and trade size 4", the test requirements of the two standards are identical, as far as what current is required to be withstood for what time period. (For 4" that's 5050A for 9 seconds). UL 467 has higher requirements for equipment intended for use with conductors larger than 3/0 Cu, while UL 514B's requirements do not increase for sizes beyond 3/0 Cu.

So it seems to me that a threadless connector, in conjunction with the provided locknut, does meet the requirements 250.5(B)(3), and is not prohibited for 250.5(B) bonding by the clause that excludes "standard locknuts" as the "only means" of bonding. Moreover, in terms of actual test performance, up through trade size 4", a bonding bushing listed to UL 467 has not been tested to a higher standard than a threadless rigid connector has been.

Cheers, Wayne

Thank you for this, the details about UL testing are very interesting. Which (to me) means a standard compression connection is compliant. @infinity, curious of your thoughts. Thx!

 

[infinity]

Thank you for this, the details about UL testing are very interesting. Which (to me) means a standard compression connection is compliant. @infinity, curious of your thoughts. Thx!

My opinion is the same. The section clearly states that the standard locknut that comes on the connector can only be used for the mechanical connection.

 

[wwhitney]

The section clearly states that the standard locknut that comes on the connector can only be used for the mechanical connection.

It does not say that. It says that standard locknuts shall not be "the only means of bonding". That refers to using two locknuts on a threaded piece of conduit. Locknuts under UL 514B are only subjected to mechanical tests, IIRC.

But a connector and its included locknut is not "only locknuts," it is a connector plus a possibly non-standard locknut. It is subjected under UL 514B to the same current test as a grounding bushing or grounding locknut is subjected to under UL 467. Adding a grounding bushing or grounding locknut to a listed connector is redundant and not required by the text of 250.92(B).

I was under the same impression as you until I closely read the words you bolded and decided to check the UL standards.

Cheers, Wayne

 

[electrofelon]

It does not say that. It says that standard locknuts shall not be "the only means of bonding". That refers to using two locknuts on a threaded piece of conduit. Locknuts under UL 514B are only subjected to mechanical tests, IIRC.

But a connector and its included locknut is not "only locknuts," it is a connector plus a possibly non-standard locknut. It is subjected under UL 514B to the same current test as a grounding bushing or grounding locknut is subjected to under UL 467. Adding a grounding bushing or grounding locknut to a listed connector is redundant and not required by the text of 250.92(B).

I was under the same impression as you until I closely read the words you bolded and decided to check the UL standards.

Cheers, Wayne

Interesting

 

[letgomywago]

It does not say that. It says that standard locknuts shall not be "the only means of bonding". That refers to using two locknuts on a threaded piece of conduit. Locknuts under UL 514B are only subjected to mechanical tests, IIRC.

But a connector and its included locknut is not "only locknuts," it is a connector plus a possibly non-standard locknut. It is subjected under UL 514B to the same current test as a grounding bushing or grounding locknut is subjected to under UL 467. Adding a grounding bushing or grounding locknut to a listed connector is redundant and not required by the text of 250.92(B).

I was under the same impression as you until I closely read the words you bolded and decided to check the UL standards.

Cheers, Wayne

This could be a game changer if I can get some more substantiation. That'd mean rigid box connectors wouldn't need bushings over 250v to ground then

 

[wwhitney]

FWIW, this article agrees that a threadless connector suffices for service bonding for terminating a metal raceway to a metal enclosure, per 250.92(B)(3):

Grounding and Bonding — Part 1 of 3

New 2011 NEC revisions clear up confusion between bonding and grounding

www.ecmweb.com

"The NEC gives you the choice of four methods for ensuring electrical continuity at service equipment, service raceways, and service conductor enclosures [250.92(B)]: . . . (3)Threadless fittings. Terminate metal raceways to metal enclosures by threadless fittings (if made tight)."

I think Mike Holt agrees, although his comment "(3)Terminate metal raceways to threadless fittings" is a bit more terse than the above.

Bonding and Grounding, based on the 2020 NEC

CLICK HERE to read the newsletter; please share it with your colleagues.

www.mikeholt.com

Cheers, Wayne

 

[Dsg319]

My opinion is the same. The section clearly states that the standard locknut that comes on the connector can only be used for the mechanical connection.

How about locknuts on LFMC connectors? Are they only made for the mechanical connection I have never even bothered to look it up.

 

[letgomywago]

How about locknuts on LFMC connectors? Are they only made for the mechanical connection I have never even bothered to look it up.

The actual conduit is only good for bonding up to 20a for 6ft anyways under 150v to ground. Thats not different in a positive way from standard locknut

 

[Dsg319]

The actual conduit is only good for bonding up to 20a for 6ft anyways under 150v to ground. Thats not different in a positive way from standard locknut

Gotcha I should have thought about that. I’m always required to pull a wire type EGC in my line of work anyways. Since the LFMC has limitations to being used on a raceway EGC is bonding bushings ever required in these connectors?