When to use SP or DP Switched Sockets?

Discussion in 'Electricians' Talk' started by Poucha, Jul 7, 2015.

  1. Poucha

    Poucha Member

    I'm looking to completely change out all my switches/sockets for nice new ones so I want to understand whether there are any circumstances where you actually need double pole.

    I understand what SP and DP mean but haven't been able to find any guide or rule which says when you should use each type. Some people say DP is "better" or safer but there doesn't seem to be any evidence of that (and apparently DP can sometimes cause RCD trips).
    It's not just about the cost - I don't mind spending more if there's a good reason for it.

    ...so intelligent answers/advice please!... and yes, I know I should employ a qualified electrician for some circuits :)
     
  2. Risteard

    Risteard Screwfix Select

    If you have a neutral/earth fault in an appliance causing the RCD to operate, and you simply disconnect the phase conductor by switching the socket off trying to locate the problem, then you have left the fault in circuit.
     
    Geeeham likes this.
  3. seneca

    seneca Screwfix Select

    I can't think of any particular case where DP switching of sockets is needed especially in the domestic environment.
     
  4. Coloumb

    Coloumb Screwfix Select

    The only dp isolator I know of that has to be there is the one in the cu, I think even then it's only so the install can be tested. Not 100% sure tbh. Maybe one needed for motor ctts, eg fans?
     
  5. Risteard

    Risteard Screwfix Select

    It's not only so it can be tested. It is the emergency switching for the installation, which in a domestic premises requires all live conductors to be broken.
     
  6. nigel willson

    nigel willson Screwfix Select

    All sockets are double pole just unplug them !!
     
  7. unphased

    unphased Screwfix Select

    Haven't read all the other replies dude but double pole completely isolates the load from the circuit whereas single pole is more of a functional thing. BS7671 requires that only the live is switched in a circuit if its single pole else both live and neutral if double pole. Its just an added belt and braces point of isolation.
     
  8. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    Pull the plug, best isolation you can get
     
  9. unphased

    unphased Screwfix Select

    In fact, there is no requirement to have a switch at all on a socket, its something that has crept in over the years and people think it is now compulsory. Unswitched sockets are still available, still fully compliant with Regs and still covered by a BS. You won't get decorative unswitched sockets but there is really no need for dp switched sockets. The best idea is, like Si-fi said, pull the plug out and the load is disconnected. Simples. It is a functional convenience to be able to switch off a socket and leave the plug in. That's all.
     
  10. Owain

    Owain Member

    You must use a DP switched socket or an unswitched socket for the supply to a central heating boiler, this is so it is isolated when the switch is off, as plumbers can't be relied upon to unplug the plug.
     
  11. Risteard

    Risteard Screwfix Select

    You can.
     
  12. unphased

    unphased Screwfix Select

    Well whoopee.
     
  13. sparky Si-Fi

    sparky Si-Fi Screwfix Select


    See 537.3.25

    and

    537.3.2.6

    No reference to DP switching whatsover
     
  14. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    How many times have you turned up on an IR test and the person says " I have turned everything off so you should be fine"

    Tell them to pull the plugs out the wall and watch them frown!

    They just don't get it
     
  15. flateric

    flateric Well-Known Member

    Get some new sockets stick em on make sure the connections are sound job done. If you are not confident get a competent person in, job done................................. or read the post after post after post ............
     
  16. Ian beadnall

    Ian beadnall New Member

    So a bit of a follow up, I'm buying the sockets etc for my electrician to fit in our new coffee shop....he tends to go a little off piste when it comes to choices of personal taste.
    I understand I think about the double pole being another level of safety. We were going to fit the 2G sockets with 2 USB plugs, these don't seem to be available in DP. Any reason for this?

    Also can someone confirm any situation why it would matter to me personally or any of my customers in the coffee shop whether the sockets were SP or DP.

    Thanks a lot! Best answer gets a free coffee....must be able to collect in person!
     
  17. Coloumb

    Coloumb Screwfix Select

    I would be more worried about rcd protection than sp v's dp.
     
  18. Ian beadnall

    Ian beadnall New Member

    Yep, thats been done cheers, any chance you could reply to the actual post now? ;-)
     
  19. stateit

    stateit Screwfix Select

    MK sockets with USB outlets are DP, for one. I guess other manufacturers who use SP sockets are just trying to shave pennies off the build cost.

    In non-TN-S or TN-C-S systems (537.2.1.1) (ie TT or IT sytems) a switch for isolation has to be double pole (537.2.21). If the isolator for a piece of equipment is a switch in a 13A socket, it should be DP. (Table 53.4 - 13A plug & socket as isolator)
     
    Last edited: Oct 18, 2015
    FatHands likes this.
  20. Ian beadnall

    Ian beadnall New Member

    Cheers for that Stateit, so screwfix are doing 2 for £18 SP, whereas MK's are £25 each. I can't justify that and don't really see how there could could be a problem with customers just plugging in, using an then leaving. All our sockets that are in permanent use for say, till and grinders smoothie makers will be DP.

    Am I missing something tho?
     

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