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

[kwired]

We quite often have metal service raceways (or even non service raceways for that matter) with an entrance cap on them and almost never provide bonding at the entrance cap end as long as the other end is electrically continuous with a proper fitting/cabinet/other enclosure that is also bonded.


Sure current will take all available paths, including metal components of other items not related to the electrical system. Mount a metal raceway or enclosure to sheet metal covered wall and there very well is some current at some level in that sheet metal when there is fault current in the raceway or enclosure.

 

[Carultch]

We quite often have metal service raceways (or even non service raceways for that matter) with an entrance cap on them and almost never provide bonding at the entrance cap end as long as the other end is electrically continuous with a proper fitting/cabinet/other enclosure that is also bonded.


Sure current will take all available paths, including metal components of other items not related to the electrical system. Mount a metal raceway or enclosure to sheet metal covered wall and there very well is some current at some level in that sheet metal when there is fault current in the raceway or enclosure.

Good point. I would imagine that if you'd need to bond your entire service riser/mast, that weatherheads would come with a provision to attach a direct burial lug. I don't think I've ever seen this, and I don't see anyone putting a bonding U-bolt or bonding band at the top.

 

[Fulthrotl]

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.

yep. concentric ko's suck.

for that matter, i've never used sealtite as a ground....
we are talking 6' of wire saved, and i've seen enough
sealtite in disarray to want a proper ground wire thru it.

concentric KO's, or for that matter, pre stamped KO's period,
are something best done without. then i can lay out the holes
i need, where i need. once you get past the level of j boxes,
factory ko's are just a hinderance to a clean install.

 

[ActionDave]

concentric KO's, or for that matter, pre stamped KO's period,
are something best done without. then i can lay out the holes
i need, where i need. once you get past the level of j boxes,
factory ko's are just a hinderance to a clean install.

:thumbsup::thumbsup:
And if there were an emoticon for applause I would put that in this response as well.

 

[tom baker]

All KO's are listed for bonding over 250V to ground.

KOs that are listed for over 250V to ground are hard to remove the concentrics, we often see these KOs on 4S boxes

 

[kwired]

KOs that are listed for over 250V to ground are hard to remove the concentrics, we often see these KOs on 4S boxes

Must be the brand you buy?

I mostly have used RACO boxes with more of an eccentric type KO, though I think they have a different name for it, that is listed for over 250 to ground and they punch out fairly easy.

Milbank and Midwest cabinets seem to have the worst ones I run into.
Getting the inner KO on those to break free is a pain, once it is out the others usually aren't too bad to deal with.

 

[iwire]

If the raceway contains a solidly connected EGC on both ends I don't see how there would be any arcing.

During a short circuit a loose connection at one end of LFMC could arc due to the voltage drop on the wire EGC. Don't forget the current on during a short circuit is high.

We can all agree that the wording is not clear.

I am not seeing it but I can agree to disagree.

 

[kwired]

During a short circuit a loose connection at one end of LFMC could arc due to the voltage drop on the wire EGC. Don't forget the current on during a short circuit is high.

As it could through any other conductive path that wasn't intended to carry current that is otherwise subject to this voltage drop.

You don't see any new foil backed fiberglass insulation these days but is kind of scary if you ever see it carrying stray currents from such events.

 

[iwire]

As it could through any other conductive path that wasn't intended to carry current that is otherwise subject to this voltage drop.

Unless you bond around it.

IMHO it comes down to this, you and Rob look at the 250.97 requirements only function is to continue the EGC path down the line (and certainly that is part of it) while I feel it has more to do with bonding a raceway to the enclosure.

Consider this, 250.97 is in part V. Bonding of the NEC, EGC requirements are in part VI. Equipment Grounding and Equipment Grounding Conductors

 

[iwire]

As it could through any other conductive path that wasn't intended to carry current that is otherwise subject to this voltage drop.

Actually when I think more on this statement I do not follow it.

We would not expect arcing at an EMT coupling during a ground fault as those are listed and test for grounding over 250 volts.

 

[kwired]

Actually when I think more on this statement I do not follow it.

We would not expect arcing at an EMT coupling during a ground fault as those are listed and test for grounding over 250 volts.

My comment intended to mean non electrical system items that may potentially end up carrying current during abnormal conditions. Metal siding, foil backing on insulation, metal studs, ceiling grid are just a few items that could carry fault current in addition to raceways and wire type EGC's. The more voltage drop there is in the EGC the more current may find it's way onto those other items.