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#91846 - 02/09/05 07:10 AM Bonding  
shortcircuit  Offline
Joined: Jun 2004
Posts: 608
If I were to use a piece of liquidtight flexible metal conduit to enclose service entrance conductors as allowed by 230.43(15)would I also be required to use bonding bushings on the liquidtight fittings along with the bonding jumper that is required to be routed with the liquidtight flexible metal conduit?


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#91847 - 02/09/05 09:15 AM Re: Bonding  
e57  Offline
Joined: May 2003
Posts: 2,876
Yes you would.... 250.92

Question though, Liquidtight flex service?

It's not something you would see everyday.

Mark Heller
"Well - I oughta....." -Jackie Gleason

#91848 - 02/09/05 09:31 AM Re: Bonding  
George Little  Offline
Joined: Jan 2004
Posts: 1,489
Michigan USA
My answer is Maybe. Since we are talking about Service Entrance conductors our conductor size is based on T. 250.66 or possibly 12.5% of the phase conductors. Depending on how the job is installed, you might end up with an external bonding conductor and bonding fittings on the flex. Actually I could use more details before a final call could be made.
Notice that if the entire run is LFNC no bonding conductor is required because the GroundED conductor takes care of that.

George Little

#91849 - 02/09/05 12:03 PM Re: Bonding  
cpal  Offline
Joined: May 2004
Posts: 162
Cohasset MA
The following paragraphs seem to apply:LFMC is a service raceway (230.43)The non current carrying metal parts would need to be bonded. This was pointed out some time ago in trade publications and proposals citing the discoloration of the outer jacket when the metal became a parallel path for stray current.I think 99 ROP for 250.30.

250.92 Services.
(A) Bonding of Services. The non–current-carrying metal parts of equipment indicated in 250.92(A)(1), (A)(2), and (A)(3) shall be effectively bonded together.
(1) The service raceways, cable trays, cablebus framework, auxiliary gutters, or service cable armor or sheath except as permitted in 250.84.

The method of bonding on the line side of the service equipment should comply with the following. I think in your case Item 4 will work but again I haven't seen the installation.

(B) Method of Bonding at the Service. Electrical continuity at service equipment, service raceways, and service conductor enclosures shall be ensured by one of the following methods:
(1) Bonding equipment to the grounded service conductor in a manner provided in 250.8
(2) Connections utilizing threaded couplings or threaded bosses on enclosures where made up wrenchtight
(3) Threadless couplings and connectors where 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


#91850 - 02/09/05 07:45 PM Re: Bonding  
shortcircuit  Offline
Joined: Jun 2004
Posts: 608
thanx for the replies guys...230.43(15)specifies that a equipment bonding jumper is to be routed with the LFMC or FMC enclosing service entrance conductors...which is allowed either inside or outside the raceway.

With this bonding jumper installed it will provide a properly sized parallel path for the neutral current to flow if the grounded conductor is interrupted for whatever reason.This bonding jumper is required because we do not want the metal of the LMFC or FMC to carry this stray current.

So with this properly installed bonding jumper...which is continuous either outside or inside the flex...I must also bond the associated LFMC or FMC and fittings again...which would provide a third path for stray current.

Do I got this right?

(I know I could just put in LFNC and forget the bonding, but I want to understand the correct bonding method for the above)


#91851 - 02/09/05 07:56 PM Re: Bonding  
cpal  Offline
Joined: May 2004
Posts: 162
Cohasset MA
I see your point but on the other hand what would happen if the metal of the liquidtight were to be come part of the circuit and it was isolated. Fault current might attempt to seek the grounded conductor at the service point and there could be arcing at loose fittings (interconnecting metal enclosures for example). I would expect carbonization and poor conductivity. Possibly a lower current flow than that required to cause OCP to clear a fault.

A unabated current flow will obviously raise the potential to ground on all of the parts of the system , create heat, we could have an electrocution or cause combustion.

250.92(A) seems to me to take the guess work out of our hands. It's metal, it's part of the raceway system and it's on the line side of the service.


[This message has been edited by cpal (edited 02-09-2005).]

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