Liquid tight flexible metal conduit

[alfre]

Hello. I'm working as and Quality Assurance inspector at a mass transportation system project (electrical train). Since I do oversight inspections for the fixed facilities at the stations, I've encountered all sort of situations in which the code applies, but there is one situation I've not been able to refer to the code. The electrical contractor has begun using liquid tight flexible conduit for the electrical runs that are to be embedded. I could not find whether the code permits or rejects this .

Thanks.

 

[tom baker]

Re: Liquid tight flexible metal conduit

See section 350.10:

350.10 Uses Permitted.
LFMC shall be permitted to be used in exposed or concealed locations as follows:
(1) Where conditions of installation, operation, or maintenance require flexibility or protection from liquids, vapors, or solids
(2) As permitted by 501.4(B), 502.4, 503.3, and 504.20 and in other hazardous (classified) locations where specifically approved, and by 553.7(B)
(3) For direct burial where listed and marked for the purpose

By contrast see under RMC 334.10
344.10 Uses Permitted.
(A) All Atmospheric Conditions and Occupancies. Use of RMC shall be permitted under all atmospheric conditions and occupancies. Ferrous raceways and fittings protected from corrosion solely by enamel shall be permitted only indoors and in occupancies not subject to severe corrosive influences.
(B) Corrosion Environments. RMC, elbows, couplings, and fittings shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition.
(C) Cinder Fill. RMC shall be permitted to be installed in or under cinder fill where subject to permanent moisture where protected on all sides by a layer of noncinder concrete not less than 50 mm (2 in.) thick; where the conduit is not less than 450 mm (18 in.) under the fill; or where protected by corrosion protection and judged suitable for the condition.
(D) Wet Locations. All supports, bolts, straps, screws, and so forth, shall be of corrosion-resistant materials or protected against corrosion by corrosion-resistant materials.

Section 300.6 states:
(B) In Concrete or in Direct Contact with the Earth. Ferrous or nonferrous metal raceways, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, fittings, supports, and support hardware shall be permitted to be installed in concrete or in direct contact with the earth, or in areas subject to severe corrosive influences where made of material judged suitable for the condition, or where provided with corrosion protection approved for the condition.

However the answer to your question is in the UL General Information Directory:
LTFMC suitable for direct burial and in poured concrete is marked "direct burial" ....

Next check a manufacturers catalog such as T&B and see if the flex and fittings are described as being suitable for concrete encasement.
I suggest you call UL and get a copy of the White Book, Green and Red Book. They may give you a set or you might have to buy them. for what you are doing it would be very valuable.

[ June 10, 2003, 10:36 PM: Message edited by: tom baker ]