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  • FIRST POST
    • dargoon
    • By dargoon 15th May 17, 10:00 PM
    • 8Posts
    • 2Thanks
    dargoon
    new breaker required
    • #1
    • 15th May 17, 10:00 PM
    new breaker required 15th May 17 at 10:00 PM
    just had a service call to our Mira shower and afterwards the chap gave me a paper stating that the breaker in the MK c.u.was 40 and should be 45. I have no idea how to change it but it seems such a small but quick job for an electrician. Assuming I can get somebody any idea of the likely cost ( Thames Valley) tia.
Page 1
    • Risteard
    • By Risteard 15th May 17, 11:43 PM
    • 661 Posts
    • 212 Thanks
    Risteard
    • #2
    • 15th May 17, 11:43 PM
    • #2
    • 15th May 17, 11:43 PM
    What is the rating of the shower?

    It's also possible that a 45A device does not exist for that distribution board. Also it will depend on the cross-sectional area and installation method of the cable. So it may not simply be a matter of uprating the protective device.
    • macman
    • By macman 16th May 17, 10:15 AM
    • 41,321 Posts
    • 16,984 Thanks
    macman
    • #3
    • 16th May 17, 10:15 AM
    • #3
    • 16th May 17, 10:15 AM
    45A MCB is a fiver or less, plus your sparky's min charge.
    No free lunch, and no free laptop
    • Risteard
    • By Risteard 16th May 17, 12:23 PM
    • 661 Posts
    • 212 Thanks
    Risteard
    • #4
    • 16th May 17, 12:23 PM
    • #4
    • 16th May 17, 12:23 PM
    45A MCB is a fiver or less
    Originally posted by macman
    Or more, or not available. (Or not appropriate.)

    You don't know what type/csa of cable is there; how it is installed; what make of distribution board is there; the rating of the shower or whether additional protection has been provided.
    • MisterP123
    • By MisterP123 16th May 17, 1:16 PM
    • 161 Posts
    • 180 Thanks
    MisterP123
    • #5
    • 16th May 17, 1:16 PM
    • #5
    • 16th May 17, 1:16 PM
    Woaah there. Slow down.

    Listen to Risteard, you can't just go chopping and changing MCB's.

    Have you ever had any problems with the shower tripping? Assuming it's a B Curve breaker and you haven't, I wouldn't touch it.

    If it's a C, it probably needs investigating as to whether disconnection times are being met.

    But we'd need a whole lot more information before recommending you replace the MCB with a 45A type B
    • shaun from Africa
    • By shaun from Africa 16th May 17, 1:22 PM
    • 9,492 Posts
    • 10,664 Thanks
    shaun from Africa
    • #6
    • 16th May 17, 1:22 PM
    • #6
    • 16th May 17, 1:22 PM
    Woaah there. Slow down.

    Listen to Risteard, you can't just go chopping and changing MCB's.

    Have you ever had any problems with the shower tripping? Assuming it's a B Curve breaker and you haven't, I wouldn't touch it.

    If it's a C, it probably needs investigating as to whether disconnection times are being met.

    But we'd need a whole lot more information before recommending you replace the MCB with a 45A type B
    Originally posted by MisterP123

    But macman didn't suggest that the OP replaced the breaker themselves.
    If they are getting an electrician in to do the work then surely those considerations would be something for that electrician to look into.
    • MisterP123
    • By MisterP123 16th May 17, 1:53 PM
    • 161 Posts
    • 180 Thanks
    MisterP123
    • #7
    • 16th May 17, 1:53 PM
    • #7
    • 16th May 17, 1:53 PM
    But macman didn't suggest that the OP replaced the breaker themselves.
    If they are getting an electrician in to do the work then surely those considerations would be something for that electrician to look into.
    Originally posted by shaun from Africa
    The OP hasn't suggested that there's a problem with the shower tripping so if it's a type B, there's no reason to change anything.

    If it's a type C, then perhaps the original installation was checked for disconnection times and still complies.

    Look at the MCB, if it's says B40 on the front, just leave it alone if you're not having any problems.
    • dargoon
    • By dargoon 16th May 17, 9:23 PM
    • 8 Posts
    • 2 Thanks
    dargoon
    • #8
    • 16th May 17, 9:23 PM
    • #8
    • 16th May 17, 9:23 PM
    Thanks to all for replies,I'll try and answer questions where possible. The shower is 9.5 or 10.8kw I am unsure which, I had 10mm cable fitted. It is exposed from the MK c.u. under the stairs through the airing cupboard to the loft and I saw the man check the length of the cable run beforehand. we called Mira because the shower ran cold only one morning. we had no prior faults recently. The engineer came and fitted a thermal trip assembly. On this visit he checked the consumer unit and this resulted on the paper with the 45mcb recommendation.
    • GDB2222
    • By GDB2222 16th May 17, 10:39 PM
    • 14,002 Posts
    • 75,302 Thanks
    GDB2222
    • #9
    • 16th May 17, 10:39 PM
    • #9
    • 16th May 17, 10:39 PM
    If 10mm cable is surface clipped to the wall, not covered at all, it should be good for over 60 A. 64 according to my chart, to be precise.
    No reliance should be placed on the above! Absolutely none, do you hear?
    • MisterP123
    • By MisterP123 17th May 17, 9:53 AM
    • 161 Posts
    • 180 Thanks
    MisterP123
    Are you having issues with the MCB tripping?

    If you're not, just leave it. Seems an unnecessary waste of time and money.

    Remember;
    "If it's not broke, don't fix it."

    Not as we say in work;
    "If it's not broke, fix it until it is!"


    You only need to change it if it's giving you problems. My partner's sister just moved into her late gran's house. Gran had lived there for years with a shower on a 40A MCB, no problems at all. Sister and two kids move in, multiple showers one after the other and MCB trips. I was around at the time and checked it. 45A MCB was needed and could be safely installed, so was done.
    • Ectophile
    • By Ectophile 17th May 17, 11:04 PM
    • 2,734 Posts
    • 1,676 Thanks
    Ectophile
    If it's a 9.5kW shower, assuming that the rating is quoted at 240V (even though we are officially on 230V these days), then the maximum current is 9500/240 = 39.5A. So no problem on a 40A breaker.

    If it's a 10.8kW, then that's 10800/240=45A exactly. A 40A breaker probably won't trip. But it's a bit poor relying on that.
    If it sticks, force it.
    If it breaks, well it wasn't working right anyway.
    • Risteard
    • By Risteard 17th May 17, 11:07 PM
    • 661 Posts
    • 212 Thanks
    Risteard
    A 40A breaker probably won't trip.
    Originally posted by Ectophile
    Actually, it's guaranteed not to trip. A circuit breaker to BS EN 60898 MUST NOT operate before 1.13 times its rated current, and must operate within 1 hour at 1.45 times. That said, it is wrong and non-compliant to fit an underrated circuit breaker and it may run hotter than intended.
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