flexible metal conduit

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Re: flexible metal conduit

Stew if that was the entire question it is unfair.

Where the flexible metal conduit and the fittings listed for grounding?

If yes as long a distance as you want.

250.118(5)Flexible metal conduit where both the conduit and fittings are listed for grounding.
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If the flexible metal conduit was not listed for grounding then these rules apply.

250.118(6)Listed flexible metal conduit that is not listed for grounding, meeting all the following conditions:

a.The conduit is terminated in fittings listed for grounding.

b.The circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.

c.The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground return path does not exceed 1.8 m (6 ft).

d.The conduit is not installed for flexibility.
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Re: flexible metal conduit

From the UL Guide for listed flexible metal conduit.
Flexible metal conduit no longer than six ft and containing circuit conductors protected by overcurrent devices rated at 20 A or less is suitable as a grounding means. Flexible metal conduit longer than six ft has not been judged to be suitable as a grounding means.
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Don
 
Re: flexible metal conduit

I knew this was not truley a fair question but what do you do during an interview. Rather than argue the point I answered 6 ft as I knew that FMT was ok at that length per 250.118(8). The reqyuirement for fmc however is in 348.60 and it states where used for flexibility and equip grn cond must be installed . All lengths as far as I can see. So it seems that the answer should have beeen that no length is acceptable WITHOUT an equip gnd cond.
Except that now that I reread 250.118 6 c as long as listed fitting are used then 6 ft is proper. My next question is under d they state where it is NOT for flexibility. In motor applications that is precicley the reason that flex is used so it seems a bit cornfusing.

[ April 22, 2005, 07:39 PM: Message edited by: stew ]
 
Re: flexible metal conduit

let me give a stab on the flex issue. I look at flex in two ways, 3/8" for fixture, can whips, that should not require a GC, but that depends on what town you're in, and most do require pulling a ground no matter what length, fittings, etc. The second way would be for pumps, motors, compressors, etc where in this case the size will always be over 3/8" and a gc will always be pulled through, and the reason for use is due to the vibration and movement issues.

Hank

N. Il
 
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