Question about bonding over 250 Volts

[JJWalecka]

I'm installing 277 volt Metal-clad Cable (MC) with the use of connectors that do not use a locknut. The connectors have a screw that when tightened it compresses the metal-clad cable and secures it in the panel, box, etc. Would those type of connectors be listed for such a use.

250.97 bonding for over 250 Volts. For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in 250.92 (B) except for (1)
Exception (d) Listed fittings that are identified for the purpose. I appreciate your input.

Justin W

 

[George Stolz]

Re: Question about bonding over 250 Volts

http://www.bptfittings.com/catalog/metal_clad.shtml

Can you put up a picture of one? If you know the part number, you can probably look it up online.

 

[infinity]

Re: Question about bonding over 250 Volts

Sounds to me like 250.97 would allow the use of these connectors on MC cable since the outer metal sheath is not a listed equipment grounding conductor. If you were to use Armored Cable (BX) where the outer metal sheath were used as the grounding conductor than the connector would need to contain one locknut as it says in Exception (3). That is unless the fitting itself were listed for bonding over 250 volts with out a locknut. All of this is contingent upon, that the KO in the box, cabinet etc. is punched for the exact size if the fitting. Oversized, concentric or eccentric KO's would require the use of additional bonding equipment.

 

[mc5w]

Re: Question about bonding over 250 Volts

If your MC cable has interlocking armor then the sheath is not a qualified equipment grounding path. However, the sheath still needs to be grounded and to be paranoid you should clean the sheath with some silicon carbide paper and stick some Noalox(R) or Penetrox(R) A or A13 on it to facilitate contact with the box connector.

Even with Corruclad(R) I would want to have a green wire inside of the cable so that I have 2 grounding paths even on 120 volts. Same goes for any kind of metal conduit. I have opened up enough walls and reconnected a conduit box connector enough times (once) to know why the British require redundant grounding conductors in all metal conduits in all occupancies and not just in hospitals.

Using just the sheath and grounding strip of type AC cable is asking for trouble. On short circuits type AC cable without a green wire inside heats up tremendously.

 

[JJWalecka]

Re: Question about bonding over 250 Volts

Georgestolz, Infinity, and MC5W thank you for your time.
The connectors are Steel MC/AC/FMC E-Z Lock Connectors. The Application states:
Used to connect steel interlocked, aluminum interlocked and aluminum corrugated metal clad cable, 3/8" FMC (570-MC & 575-MC) or 1/2" FMC (577-MC) to box or enclosure. Insulator rated 105? C.
It also states a UL Listed number that I would presume would or wouldn't list it for the application of connecting 250 Volts or greater. If I have time I will try to look up the UL Listed number.

Justin W.