Showers again - RCBO or RCD?

Discussion in 'Electricians' Talk' started by stu22, May 19, 2004.

  1. stu22

    stu22 New Member

    Hello,

    Please could one of you kind Pro's help me out of my confusion - i am trying to understand the protection needed for a 10.5kW shower (NO, i will not be doing any wiring, but i'm just trying to understand the jargon!)

    My questions/confusions are:

    Would an RCBO offer better protection than an RCD?

    Would you put the RCBO on the RCD side of a split CU? WHy?

    Do RCBO's come as 2 pole, or are they only concerned with the phase wire? (Please can someone explain this a bit? I thought it's be better to cut off live and neutral in the event of a fault?). If they are available, who makes them?

    For a 10.5kW shower, 10mm cable, would 50A RCBO in the 63A RCD side of the split CU make sense (i know it doesn't leave much room for other things on the RCD side of the CU).

    I'm just trying to understand, but my brain is running down the side of my head!

    Thankyou for any help,

    Stu.
  2. plugwash

    plugwash New Member

    a rcbo is essentially a rcd and a mcb in one unit so there is no point in putting one in the rcd side of the CU

    given the low rating of the rcd in your cu i would use a rcbo in the non-rcd side

    rcbos come with 2 short wires which link to the neutral and earth bars

    the cuircuit live and neutral both go into the rcbo and the cuircuit earth goes direct to the earth bar
  3. pyrotenax

    pyrotenax New Member

    An RCD is not required on a shower in a bathroom.

    REG 601-09-02 The following fixed equipment may be installed in zone 1 if it is suitable for that zone.
    a water heater
    (ii) a shower pump.
  4. plugwash

    plugwash New Member

    sure its not required by wiring regs
    but
    1: most shower manaufacturers tell you to to do it
    2: do you really wan't a cuircuit on the largest fuse in your house near a place where you will be naked and soaked without rcd protection
  5. unphased

    unphased Screwfix Select

    >
    My questions/confusions are:

    Would an RCBO offer better protection than an RCD?
    >
    Essentially one and the same (see below). RCD is a generic term used to identify a device which will "break" circuit under certain fault conditions. They are used principally to protect against earth leakage type faults.

    Would you put the RCBO on the RCD side of a split CU?
    WHy?


    An RCBO is a device which combines the functions of an RCD and overcurrent protection. If you wanted to use an RCBO it would be on a non-RCD protected circuit as a convenient means of providing one.

    Do RCBO's come as 2 pole, or are they only concerned
    with the phase wire? (Please can someone explain this
    a bit? I thought it's be better to cut off live and
    neutral in the event of a fault?). If they are
    available, who makes them?
    >

    RCBO's are a double pole device which will isolate the phase and neutral when they operate. Because of the way they monitor the circuit for a fault they need to be connected to the phase and neutral on the SAME circuit. (An RCD switch will be monitoring faults on ALL groups of circuits connected on the RCD side of the switch connected to the same neutral bar). They look for an imbalance in the phase and neutral currents and see this as a fault and will trip. You can get single module devicces to sit in the same space as an MCB but RCD's used as main switches will generally be a two module type. (Four pole versions are used on 3 ph supplies). The vast majority of protective devices utilise phase as the the conductor to isolate and it is illegal to switch a neutral conductor instead. You are correct that isolation of both ph an n is "better" but total isolation is rarely necessary at every point on a circuit only at the origin is it needed.

    For a 10.5kW shower, 10mm cable, would 50A RCBO in
    the 63A RCD side of the split CU make sense (i know
    it doesn't leave much room for other things on the
    RCD side of the CU).
    >

    The cable size is correct but as discussed previously no need to double up an RCD with an RCBO. You would use a 63A 30mA rated RCD and a standard 50A MCB on the circuit as a fuse.

    I'm just trying to understand, but my brain is
    running down the side of my head!


    Yuch!

    > Thankyou for any help,

    Your welcome.

    Stu.
  6. unphased

    unphased Screwfix Select

    pyro this point has been subject an FAQ on the forum. Yes you dont technically require to have a shower on an RCD but the shower manufacturers and most sensible sparkies think they are a good idea to have.
  7. stu22

    stu22 New Member

    Thankyou everyone! I now have a better understanding of what people are talking about.

    Best Regards,

    Stu.

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