new breaker required

dargoon · 15 May 2017 at 10:00PM

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.

Risteard · 15 May 2017 at 11:43PM

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 · 16 May 2017 at 10:15AM

45A MCB is a fiver or less, plus your sparky's min charge.

Risteard · 16 May 2017 at 12:23PM

macman wrote: »

45A MCB is a fiver or less

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 · 16 May 2017 at 1:16PM

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 · 16 May 2017 at 1:22PM

MisterP123 wrote: »

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

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 · 16 May 2017 at 1:53PM

shaun_from_Africa wrote: »

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.

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 · 16 May 2017 at 9:23PM

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 · 16 May 2017 at 10:39PM

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.

MisterP123 · 17 May 2017 at 9:53AM

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 · 17 May 2017 at 11:04PM

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.

new breaker required

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