Seal-tite (LFMC) connectors in concentric K/Os

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Johnnybob

Senior Member
Location
Colville, WA
Good afternoon, everyone, and thanks in advance for your time:)
So a question came up yesterday while installing a couple of disconnects. When using LFMC connectors in concentric KO's in an enclosure, do I need to use grounding/bonding bushings? If so, can I please have a code reference? I avoided the issue by drilling holes, but I would realy like to know so I can give/reference correct information!
Thank you,
JC
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I assume this is not for a service so for circuits over 250v to ground see 250.97 otherwise I don't believe you will need bonding bushing. Is there an equipment grounding conductor in the flex? If not look at 250.118
 

Johnnybob

Senior Member
Location
Colville, WA
I assume this is not for a service so for circuits over 250v to ground see 250.97 otherwise I don't believe you will need bonding bushing. Is there an equipment grounding conductor in the flex? If not look at 250.118
No, not service. Remote disconnects in a sawmill, 480V.
Thank you, Dennis
 

Carultch

Senior Member
Location
Massachusetts
Good afternoon, everyone, and thanks in advance for your time:)
So a question came up yesterday while installing a couple of disconnects. When using LFMC connectors in concentric KO's in an enclosure, do I need to use grounding/bonding bushings? If so, can I please have a code reference? I avoided the issue by drilling holes, but I would realy like to know so I can give/reference correct information!
Thank you,
JC

It is concentric knockouts remaining that matters. If you use up all concentric ko's, it is the same bonding condition as if they never were there to begin with.

Given that it is not a service raceway and no GEC's are present
>250V to ground nominal - yes, unless KOs are otherwise listed for grounding at this voltage
250 V to ground nominal and less, no. Standard locknuts and connector locknuts suffice for electrical continuity.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Disconnect switches do not have their KO's evaluated as suitable for grounding for over 250 volts. From UL:

Other Types of Metallic Enclosures
Cabinets and cutout boxes, in accordance
with NEC Article 312, as well as junction and
pull boxes, in accordance with NEC Article
314, may also employ concentric or eccentric
knockouts, and are evaluated for UL Listing
in accordance with UL 50, the Standard for
Safety for Enclosures for Electrical Equipment
(CYIV and BGUZ).
In contrast with metallic outlet boxes, these
other types of metallic enclosures with
concentric or eccentric knockouts are not
required to be subjected to a short time cur-
rent test. As such, NEC Section 250.97 would
require that bonding jumpers be used unless
all concentric or eccentric knockouts were
removed. For UL Guide Information, please
refer to pages 69 and 84 of the 2008 Edi-
tion of the UL White Book for these product
categories, or view this information online
at www.ul.com/database. Enter “CYIV”
or “BGUZ” into the database field for “UL
Category Code.”


http://forums.mikeholt.com/showthread.php?t=173541
 

kwired

Electron manager
Location
NE Nebraska
I do not believe that changes the requirements of 250.97
If the raceway in question contains an EGC, IMO only one side of the raceway needs to comply with that section, the raceway still has suitable conductivity to a properly bonded box the raceway is bonded.

If the raceway is used as the EGC, then I think you have no choice, both ends need to comply.

There should be nothing wrong with one end landing at a non metallic enclosure or adapted to NM raceway either - as long as the other end sees proper bonding, or other means are used to accomplish bonding it.
 

kwired

Electron manager
Location
NE Nebraska
I knew what you meant and i think your logic is sound I still don't think that changes the requirements in 250.97
I can see your interpretation of it.

I don't think it is worded clearly enough to claim either way is what may have been intended.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
If the raceway in question contains an EGC, IMO only one side of the raceway needs to comply with that section, the raceway still has suitable conductivity to a properly bonded box the raceway is bonded.

If the raceway is used as the EGC, then I think you have no choice, both ends need to comply.

There should be nothing wrong with one end landing at a non metallic enclosure or adapted to NM raceway either - as long as the other end sees proper bonding, or other means are used to accomplish bonding it.

I am wondering if your reply is the same thing I am thinking...

Under 250 volts to ground is a no brainer. Concentric KO's or exact sized hole you have the same rules.

Over 250 volts to ground (which the OP has) and you have additional rules. First off, the enclosure, if metallic, can't rely on the flex as the sole source of bonding regardless of its length. So, a green or bare grounding conductor must be run with it, or a properly installed bonding locknut or bond bushing or other approved method must be used.

Second and separate code section issue. Exposed metal parts of the raceway, such as the fitting, must be properly bonded. The concentric knockout does not provide this bond for the flex, so if the other end of the flex is properly bonded to the grounding system, then you are right back to needing the above bonding, even if a separate ground conductor is run. So, for example. if the home run is PVC, up out of the ground with a rigid metal stub and the a piece of flex, the stub and the flex aren't bonded and a bond has to be provided.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
I use RE washers to cover the largest KO in the disconnect, required or not. I've seen too many pieces of flex hanging by the wires....
 

iwire

Moderator
Staff member
Location
Massachusetts
I use RE washers to cover the largest KO in the disconnect, required or not. I've seen too many pieces of flex hanging by the wires....

Literally just did the same yesterday with an RMC, much easier to put washers on now than later when it breaks.
 

Carultch

Senior Member
Location
Massachusetts
If the raceway in question contains an EGC, IMO only one side of the raceway needs to comply with that section, the raceway still has suitable conductivity to a properly bonded box the raceway is bonded.

If the raceway is used as the EGC, then I think you have no choice, both ends need to comply.

There should be nothing wrong with one end landing at a non metallic enclosure or adapted to NM raceway either - as long as the other end sees proper bonding, or other means are used to accomplish bonding it.

I've wondered about this myself. Whether there is a difference between a fitting-to-enclosure connection that is electrically discontinuous (non-metal enclosure), and the contrary which is a fitting-to-enclosure connection of insufficient electrical continuity (as is the case with ring KOs remaining and >250V-g). Both in the context of not needing this continuity.

If a wire EGC is present, I would think that non-service metal conduit only needs to bonded on one end, to establish that it is a non-current carrying conductor that is grounded.

However, fault current takes all paths possible, and not just the "preferred" wire EGC path. If some of it passes through the ring KO with insufficient continuity, is the excess heat a problem? That is the reason a conservative solution is to add more substantial grounding fittings, and avoid building with a "dead end" conduit ground. This wouldn't happen when it terminates on a nonmetal enclosure, because there isn't continuity. But in concept, it could happen on a metal enclosure with insufficient ring KO continuity.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
If the raceway in question contains an EGC, IMO only one side of the raceway needs to comply with that section, the raceway still has suitable conductivity to a properly bonded box the raceway is bonded.

If the raceway is used as the EGC, then I think you have no choice, both ends need to comply.

There should be nothing wrong with one end landing at a non metallic enclosure or adapted to NM raceway either - as long as the other end sees proper bonding, or other means are used to accomplish bonding it.

I agree, once you interject the nonmetallic portion of the conduit run argument into the conversation it makes sense to say that bonding on one end is sufficient.
 

iwire

Moderator
Staff member
Location
Massachusetts
I agree, once you interject the nonmetallic portion of the conduit run argument into the conversation it makes sense to say that bonding on one end is sufficient.

Except that we are not talking about plastic here.

You and kwired seem to be looking at 250.97s function as only continuing an EGC, I feel it is more than that.


Regardless of the internal EGC you could have arcing between the LFMC and the enclosure.


See this thread for some semi related discussions about arcing even with a complete wire EGC. http://forums.mikeholt.com/showthread.php?t=174148
 
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infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
If the raceway contains a solidly connected EGC on both ends I don't see how there would be any arcing. We can all agree that the wording is not clear.
 
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