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jhack (Mechanical)
4 Mar 11 14:53
Hello,

I have several automatic shutoff valve assemblies (see example below)which have both a solenoid and a proof of closure limit switch, both of which are rated for a class 1 div 2 application.  In a non hazardous environment we would typically run a short peice of liquid-tight flexible conduit from the solenoid to the switch and then bring a single cable back from the switch to my cabinet.  However, in my experience this type of polymer coated conduit is not allowed for this hazardous location. Either rigid or at flexible metal conduit with an outer metal braid is required.  I have not been able to find a flexible conduit which carries a class 1 div 2 rating, and I would prefer not to use rigid.  Has anyone run into a similar problem or have any suggestions?

Regards

jhack





The NEC 70 section which covers this is as follows:

(B) Class I, Division 2.

(1) General. In Class I, Division 2 locations, the following wiring methods shall be permitted:  
(1) All wiring methods permitted in Article 501.4(A).
(2) Threaded rigid metal conduit, threaded steel intermediate metal conduit.
(3) Enclosed gasketed busways, enclosed gasketed wireways.
(4) Type PLTC cable in accordance with the provisions of Article 725, or in cable tray systems. PLTC shall be installed in a manner to avoid tensile stress at the termination fittings.
(5) Type ITC cable in cable trays, in raceways, supported by messenger wire, afforded mechanical protection and run as open wiring, or directly buried where the cable is listed for this use.
(6) Type MI, MC, MV, or TC cable with termination fittings, or in cable tray systems and installed in a manner to avoid tensile stress at the termination fittings.

(2) Flexible Connections. Where provision must be made for limited flexibility, flexible metal fittings, flexible metal conduit with listed fittings, liquidtight flexible metal conduit with listed fittings, liquidtight flexible nonmetallic conduit with listed fittings, or flexible cord listed for extra-hard usage and provided with listed bushed fittings shall be used. An additional conductor for grounding shall be included in the flexible cord.
FPN: See 501.16(B) for grounding requirements where flexible conduit is used.

 
Helpful Member!  DRWeig (Electrical)
7 Mar 11 10:07
Hi JHack,

My read of those paragraphs has always been that liquidtight is OK but the fittings need to be listed.  

Southwire and Thomas & Betts in the US have such listed fittings, and even print the applicability of the flex in their data sheets.  Try googling the following for mroe manufacturers and sources:

liquidtight flexible nonmetallic conduit class 1 div 2

Most important, though -- ask the authority having jurisdiction how he or she interprets the code.

Good on ya,

Goober Dave
Helpful Member!  rbalex (Electrical)
7 Mar 11 14:38
The critical NEC issue for "standard" Liquidtight Flexible Metal Conduit (LFMC) in Classified locations is grounding and bonding. See Section 250.30; otherwise, plain ol' vanilla LMFC is fine in Division 2. As a side note; look at the UL label on a stick of listed rigid (Art. 344, RMC). Odds are, it won't mention that it's suitable for Classified locations. Nevertheless you know it is simply because the NEC says so. It also says listed LFMC is suitable in Division 2, marked for it or not.

Goober Dave's point is also well taken; all termination fittings must be listed. However, they must be listed whether in a Classified location or not. See 350.6. In a Classified location application they must also be listed for grounding/bonding.
rbalex (Electrical)
7 Mar 11 14:43
Error in Citation See Section 501.30 NOT 250.30 (I had Art 250 (Grounding and Bonding) on the brain.
jhack (Mechanical)
7 Mar 11 17:45
Thanks to both of you for your reply.  We usually use Thomas and Betts fittings and I was able to find the section in the spec sheet which states the suitability for Class 1 Div. 2 locations.  Unfortunately the NEC code I have is 2002 and seems to be missing section 501.30.  I assume this section refers to grounding the conduit.  I was planning on running a ground wire to from the solenoid to the limit switch and then carrying this back to my cabinet ground bus (cabinet is located within 10 ft. of the valves). This would ensure a proper ground on the limit switch and solenoid regardless of whether the conduit is grounded or not.  Is this an acceptable grounding method?

The other follow up question I have is: The limit switch is rated as explosion proof.  My understanding was that this would require an explosion proof fitting at any entry point.  While the fittings I have found are Class 1 div. 2 rated this does not mean they are explosion proof. (ie. an explosion in the switch could propagate through the fitting and ignite the outside environment) Are you aware of any explosion-proof liquid-tite fittings? I have a call in to Thomas & Betts to see if they offer such a product.
rbalex (Electrical)
7 Mar 11 19:47
For the 2002 NEC, the citation would be Section 501.16. (Read the whole Section)  It is really more an issue of bonding, but the NEC still hasn't quite gotten the issue of bonding versus grounding straight yet ;) They are still ocassionally used interchangably where they shouldn't be. Also be careful that "...Such means of bonding shall apply to all intervening raceways, fittings, boxes, enclosures, and so forth between Class I locations and the point of grounding for service equipment or point of grounding of a separately derived system." This is an extremely important issue in all Class I locations, both Division 1 and 2.

Actually, if the switch is in an explosionproof enclosure you will need a seal at the unit. See NEC[2002]Section 501.5(B)(1). Since it is already in an explosionproof enclosure it is likely "... required to be..."; probably per Section 501.6(B)(1)[switches in Division 2 that are required to be identified for Division 1]

Beyond the seal, "standard" Division 2 wiring methods may be used.

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