Wiring in Hazardous area

Can someone offer a little help.I recently came across SY/CY cable used to wire some permanent fitted lights in a Hazardous area, they were also plugged in for some reason and switched on/off by twisting the EX plug. My question which I am struggling to find the answer to is SY or CY suitable for use in hazardous area? 

  • (Really just adding a reply to bring the thread to the first page so others will more likely see it)

    I presume the twisting action is a means of operating an interlocked switch on the socket (traditional caravan club site hookup style).

      - Andy. 

  • Michael,

    60079-14 the design and selection and erection standard for Haz areas indicates the following for cables for fixed wiring:

    Regarding plug/socket arrangement:

    My own opinion would be that SY/CY cable would not be suitable as the fixed wiring, nor would they meet the requirements for flexible cables due to the poor mechanical resistance.

    Apart from the UV degradation, the designer/installer also needs to ensure the cable materials will not be affected or degraded by exposure to whatever the hazardous chemical material may be.

    As long as the Plug/socket arrangement is a certified ATEX arrangement and the plug is compatible with the socket then all should be ok. For Exd protection you should never be able to remove the plug without activating the isolator on the socket and they are likley always interlocked that you cant unplug when socket is energised.

    An Exed socket and plug arrangement could be slightly diffrent.

    Hope that helps, Regards GTB

  • Having seen the specification from GTB, which PVC sheathed cable do you think is any better than SY, which will more than meet the tensile strength specification, is thermoplastic sheathed TWICE, and is probably at least as robust as the others in the list. The only one missing is a polyurethane sheathed cable, and these are more robust than any of those listed, being very tough and thermosetting. Your hazardous area is presumably an area with a potentially explosive / flammable atmosphere, and with the correct glands many kinds of cables would be suitable.

    SY can be obtained which is made to BS6500, and has BASEC approval, so I see no reason for it to be unsatisfactory, and would be a good choice if the cables are subject to movement, which you say they are when being plugged in, and vibration could also be a problem. There are not a lot of alternatives available, and polyurethane cables are unusual and expensive and again do not have a BS!

  • GTB, I too do not think SY/CY cable is not suitable for a fixed wire installation in a hazardous area. It is a PVC PVC cable This is where the plot thickens, from an inspectors point of view the lighting circuit is fixed . From the clients point of view it is a temporary installation as it is plugged in. 

  • SY or CY cable may or may not be suitable for a hazardous area- it all depends on the specifics of the hazard.

    For example Is there strong UV  -perhaps used to set adhesives or to sterilize things - though actually this makes all soft skilled PVC unsuitable, not just SY/CY  There are cables more common in the middle east and other sunny places of a screened construction but with a black UV bllocking outer. The outer sheath fails in a few years anyway of course but the inner does not start to degrade until it does.

    Are there solvents present that will attack PVC - note that most do not -  things like most kinds of paint thinners and petrol are OK in small doses.

    The flexible construction is a good thing if the cables are being twisted or wound and unwound on a regular basis. This precludes a more rigid armour or coarser stranded cores.

    Then there is the question of glanding and termination. If you have aggressive or explosive vaporous present you need glands that form an all round compression seal, much like a stuffing gland, and these may need to be of specific materials that will not be attacked, At the same time the braid of the CY or SY should be earthed to obtain maximum benefit from it, otherwise you may as well use a more conventional flex with a strength core such as the sort used for railway works. The braid should not be the sole CPC however, as it is the first part to suffer from mechanical damage.

    So what hazards are present in the area - is it just a store for jet fuel or something, or a bigger problem ?


  • Michael,

    Thanks for your comments. I also think what did the designer think? Under DSEAR 2002 and Schedule 6 the duty holder must control all sources of ignition! in other words the hierachy is dont put anything electrical in a known hazardous area, if you do then should be the absolute Minimum. As such if there was an explosion on this site and the plug/socket arrangement found to be the uncontrolled source of ignition either due to incorrect materials/equipment/poor installation etc. I would be asking why the circuit cable did not go directly into the luminaire that way you only have one certified gland to suit the fixed wiring cable and keep the Ex protection concept of the luminaire.

    By adding a plug/socket arrangement, you have now increased the Ex equipment items by two and also cable glanding/terminations by another two, hence more sources of potential ignition.

    The whole idea is to keep it simple and minimum.

    I would certainly not be putting SY/CY in this install. Then again I would likley deisgn the installation to avoid the plug/socket arerangement if I could.