LFMC ground

[lbartsch]

Our design calls for a 10" piece of 3/4" LFMC to be installed between an LB and the equipment. The conduit contains six 8 awg THHN/THWN conductors.
I would like to use the LFMC as the grounding conductor since including a 10 awg conductor inside the LFMC will exceed the fill limit of 40%. I believe that I meet all of the requirements of 250.118(7) but I'm not sure about 250.118(7)(e). There is no vibration and no expected movement, the LFMC is used to permit ease of alignment. Am I in compliance?

On another note, if I can use the LFMC as a chase nipple as per chapter 9, note (4), I can use 60% fill. Problem is, does the conduit body constitute a box or similar enclosure?

 

[tom baker]

Re: LFMC ground

Is this a NEC application? It sounds more like a UL 508 or NFPA 79 application.
However the answer to your question is in Chaper 9 Note (4). You are not limited to 40% fill for that length....

 

[lbartsch]

Re: LFMC ground

Tom,

Sorry if this was vague, yes it is an NEC issue. I should have noted that the 3/4" LFMC is between the LB conduit body (on the end of a 1" IMC run) and the user equipment.

Larry

 

[don_resqcapt19]

Re: LFMC ground

If you have installed supports as required by 350.30, then you are in compliance with the code. If there are no supports, then it must be because flexibility is required an you will have to provide a bonding jumper around the LFMC.
Don

 

[tom baker]

Re: LFMC ground

Good point by Don. I very seldom see LT flex supported as required.

 

[lbartsch]

Re: LFMC ground

I should be compliant with 350.30. The LFMC is only 10" long and should not require additional support. Its the definition of flexibility that seems to be the sticky point. We are using the LFMC to permit misalignment, is that the same as flexibilty? I do not think so. There's no vibration or movement in the equipment, its stictly for ease of installation.

 

[don_resqcapt19]

Re: LFMC ground

I don't think that you can count the flex connectors as support. It needs a support within 12" of the connectors. There is no exception that says short lengths do not require support. The only permission not to install this support that would apply in your case is Exception #2 to 350.30. This is the flexibility exception. If you don't have a support, a bonding jumper is required.
Don

 

[bennie]

Re: LFMC ground

Flexible means capable of being moved. A motor that has to be moved for belt tightening is flexible. A garbage disposal, may vibrate, but it remains in the same location, therefore it is not flexible.

 

[don_resqcapt19]

Re: LFMC ground

Bennie,
Vibration is movement, only on a small scale.
don

 

[lbartsch]

Re: LFMC ground

Don't forget, I can't support an LFMC within 12" of the connector if its only 10" long. Therefore, as I see it, since I'm not using the LFMC for "flecible" conditions (just alignment) I can use the LFMC as my bond.

Thanks to all thus far for the help...

 

[don_resqcapt19]

Re: LFMC ground

lbartsch,

Don't forget, I can't support an LFMC within 12" of the connector if its only 10" long.

Why not? A single support anywhere on the LFMC will meet the requirements of the rule. There is not an exception to the support rule, just because of the length of the conduit. In my opinion, the only reason that you are pemitted to omit the support required by 350.30(A) is by the use of Exception #2 to 350.30(A). If the support is not installed, a bonding jumper is required by the code rules. If you install the required support, the bonding jumper is not required.
Don

 

[roger deas]

Re: LFMC ground

I agree with Bennie, this connection is for the purpose of flexibility whether during the running of the equipment or for adjustments.

Roger

 

[bennie]

Re: LFMC ground

A 150 KVA transformer, connected with flex, is for sure not flexible. A transformer also vibrates.