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Compliant?

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Is this arrangement compliant or not?


Consumer unit. R.C.D. protected shower circuit supplied by a B40 M.C.B. which runs to a cord ceiling switch  in the shower room in 6.0mm2 T&E. Old electric shower removed. New power shower installed with water supplied from tanks. 0.63 Amp transformer in loft to feed new integral shower pump motor. Loft transformer fed via 3 Amp fused switched fused connection unit on a 1.0mm2 T&E cable from old shower ceiling cord switch. 1.0 mm2 T&E run 2.5 metres.


P.S. The switched fused connection unit is at the end of the supply cables.


Confirmation or condemnation by regs. please.


Z.
  • 0
    I know!  The “tanks” are the military variety and we are pumping fuel?
  • 0

    Thanks Andy,

                          the 1.0mm2 T&E is running on glass fibre flameproof insulation in a very clean and tidy environment with no rubbish or detritus near it at all. It does not run over any timber joists. I can not see any way that it can be damaged as it is under a tank stand and in an inaccessible area at the end of a loft. 



    A fault can occur in many ways - not just physical damage to the cable. In your situation I'd still be worried about the wiring behind the FCU - a fault there will still expose the full length of the first 1mm² to excessive fault current/duration. I'm sure most of us have come across the results of faults behind sockets or FCUs at some time or other - either from basic insulation having been trapped and squashed, seemingly OK at first but eventually going bang perhaps decades later; or due to loose connection or internal flaw in the accessory causing overheating and melting the insulation. The wiring to the incomer of CUs etc is usually much better than BS 1363 type accessories in that respect as the individual conductors can be run separate from each other and there's no need to squash them all into the backbox after termination, so chances of a fault can be much reduced even if the basic insulation fails. You've certainly satisfied (i) and sounds like you're happy with (iii) as well - but it still sounds to me like you might have a problem with (ii) - and BS 7671 requires all three to be satisfied.


       - Andy.
  • 0

    AJJewsbury:




    Thanks Andy,

                          the 1.0mm2 T&E is running on glass fibre flameproof insulation in a very clean and tidy environment with no rubbish or detritus near it at all. It does not run over any timber joists. I can not see any way that it can be damaged as it is under a tank stand and in an inaccessible area at the end of a loft. 



    A fault can occur in many ways - not just physical damage to the cable. In your situation I'd still be worried about the wiring behind the FCU - a fault there will still expose the full length of the first 1mm² to excessive fault current/duration. I'm sure most of us have come across the results of faults behind sockets or FCUs at some time or other - either from basic insulation having been trapped and squashed, seemingly OK at first but eventually going bang perhaps decades later; or due to loose connection or internal flaw in the accessory causing overheating and melting the insulation. The wiring to the incomer of CUs etc is usually much better than BS 1363 type accessories in that respect as the individual conductors can be run separate from each other and there's no need to squash them all into the backbox after termination, so chances of a fault can be much reduced even if the basic insulation fails. You've certainly satisfied (i) and sounds like you're happy with (iii) as well - but it still sounds to me like you might have a problem with (ii) - and BS 7671 requires all three to be satisfied.


       - Andy.

     




    Thanks Andy,

                              The connections in the fused connection unit in an insulated pattress are perfectly made off. No squeezing or squashing of conductors involved at all in the generously deep pattress. The pattress and accessory are made of flameproof urea formaldehyde. The load is 0.63 Amps maximum and fused at 3 Amp. The transformer is a B.E.A.B. approved type of excellent quality with perhaps an internal over temperature cut out. (I will have to check on that). The supply conductors have "re-enforced" electrical insulation as both are separately electrically insulated. If an earth fault occurs the 30 mA R.C.D. will swiftly disconnect the supply. I think that 434.2.1 (ii) is complied with as a L to N short circuit is almost impossible with this arrangement and very small intermittent load. that will not stress the fused connection unit.


    Also, the 1.0mm2 T&E is only live when the shower is in use, as the users will turn off the ceiling cord switch which supplies it immediately after use, to let the transformer cool down. The transformer has only a 25 per cent duty cycle according to the instructions, 15 minutes use then 45 minutes off to cool they state.


    The shower kit is an Aqualisa kit. The transformer is supplied in the kit and comes from APL Transformers of Westerham, Kent. Type 243501.


    Z.

  • 0
    Even though the power shower should be fed via a double pole isolator, the isolator should not be used during normal operation. It should be permanently connected in order for a controlled shut down to take place. The cord switch invites incorrect operation.
  • 0

    Foffer:

    Even though the power shower should be fed via a double pole isolator, the isolator should not be used during normal operation. It should be permanently connected in order for a controlled shut down to take place. The cord switch invites incorrect operation. 




    I expect that the plumber installer will discuss operation with the customers Foffer, and leave the user's instructions with them as well.


    Z.

  • 0
    Are the hot and cold supplies to the pump  properly earth bonded?
  • 0

    Foffer:

    Are the hot and cold supplies to the pump  properly earth bonded?




    The cold feed is from a plastic loft tank so is not an extraneous-conductive-part, or an exposed-conductive part as it can not be touched.


    The hot pipe is well bonded by previous installers who bonded just about every copper pipe in the airing cupboard, including the shower room metal radiator pipes and the pipes to the heated towel rail above it. All is good. 


    Z.

  • 0
    Is there still something that we've all missed?  Please let me know, it's driving me mad!  I've been retired for three years but your question has prompted me to order a copy of the 18th ed.  Should I wait for it to arrive and spend some times searching through it, or do you consider that it is compliant?
  • 0

    Is there still something that we've all missed?  Please let me know, it's driving me mad!  I've been retired for three years but your question has prompted me to order a copy of the 18th ed.  Should I wait for it to arrive and spend some times searching through it, or do you consider that it is compliant?



    I think we've agreed that the B40 can't be relied upon to provide fault protection (either L-N or L-PE) to the 1.0mm² cable. (The 30mA RCD probably won't help much either, even for L-PE faults - above 575A the energy let-though (I²t) of the RCD for 40ms will exceed the withstand (k²S²) of the cable (13,225A²s for 1mm² with k=115).)


    So we're looking at whether the three conditions of 434.2.1 to allow fault protection to be positioned downstream of the reduction of c.s.a. are satisfied. If it helps at all that particular regulation seems not to have changed for a very long time - it's practically identical to 473-6 in the 15th Ed.


    (i) 3m rule - at 2.5m long that's an easy pass.

    (ii) and (iii) are the stumbling blocks - whether it's installed in such a manner to reduce the risk of faults, fire and danger to persons, to a minimum.  I'm still not comfortable that it is - the whole setup feels to me a order of magnitude away from the situations where this regulation is normally applied, but perhaps Z (who as see it of course) is more comfortable with it?


      - Andy.

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