Flex Conduit as a ground path

[Dustin Foelber]

Good Morning
I have an apartment project that is currently in flex conduit. There is no ground in branch circuits or feeder pipes. My assumption is at some point flex was considered an adequate ground path in which no ground conductor was required. My question is primarily on the sub-feeds. If we replace the sub panel will I be required to pull a ground for the sub feed. Current wire size is adequate for load and properly protected. I had planned on putting a ground bushing on the flex connector and install a bonding jumper to the panel ground bus. Is this a violation? Also if a ground is needed am I allowed to drive a rod for each 6 units and ground sub panels to that? Or does the ground need to be in the sub feed conduit and go from panel to meter bank individually. I appreciate any input.

 

[kwired]

Flex that is composed of a spiraled metallic tape (so to speak) is not a very effective grounding conductor. I don't know how long the current requirements have been in the code. I do know that early versions of AC cable did use the sheath as a grounding conductor and they had found that there is an increased impedance in longer pieces of this and this results in poor performance as an equipment grounding conductor.

If I were to guess, I would have to say that if it was allowed to be used as an EGC in any significant length it likely would have been at least 60+ years ago.

How old is your existing installation?

 

[petersonra]

Good Morning
I have an apartment project that is currently in flex conduit. There is no ground in branch circuits or feeder pipes. My assumption is at some point flex was considered an adequate ground path in which no ground conductor was required. My question is primarily on the sub-feeds. If we replace the sub panel will I be required to pull a ground for the sub feed. Current wire size is adequate for load and properly protected. I had planned on putting a ground bushing on the flex connector and install a bonding jumper to the panel ground bus. Is this a violation?

I don't see how it could be a violation assuming you used fittings listed for the purpose. I don't know what you mean by "flex conduit". There are a bunch of different flexible conduit products out there, some are suitable for using the sheath as the EGC, some are not. IIRC, at one time Greenfield sheaths were considered adequate EGCs.

Also if a ground is needed am I allowed to drive a rod for each 6 units and ground sub panels to that? Or does the ground need to be in the sub feed conduit and go from panel to meter bank individually.

I think you are possibly confusing the EGC with a GEC. The sub-panels likely do not need a GEC, but they do need an EGC. Adding a ground rod to a sub-panel does not really deal with the lack of an effective EGC if that is your problem.

 

[kwired]

I don't see how it could be a violation assuming you used fittings listed for the purpose. I don't know what you mean by "flex conduit". There are a bunch of different flexible conduit products out there, some are suitable for using the sheath as the EGC, some are not. IIRC, at one time Greenfield sheaths were considered adequate EGCs.



I think you are possibly confusing the EGC with a GEC. The sub-panels likely do not need a GEC, but they do need an EGC. Adding a ground rod to a sub-panel does not really deal with the lack of an effective EGC if that is your problem.

Flexible metal conduits are suitable for equipment grounding, but with conditions. The main condition is the 6 foot length limitation. You can have runs longer than that, but must have an additional equipment grounding conductor installed.

 

[Dennis Alwon]

FMT is not the same as FMC. Which is it? FMC is 6' and no more than a 20 amp OCPD to use it as an EGC. 250.118

I thought I read tubing in there but don't see it now. :?