9.5 kw shower on 6mm cable - electrician says it's ok but tripping

[DetlefSchmitz]

If it were me I'd put a clamp current meter round the line wire and see how much current the shower was taking, and compare it with the MCB rating. Without doing something like that it's just guesswork. (You can get a clamp meter for under £8 on ebay.)

 

[MattB83]

The switch was refitted one week ago ,and it doesn't work properly / switch on and off ? Then replace it ,as said already. The shower on/ off may be a simple repair ,if it is not then fit a new one.
Seems odd that you have had two switches fail ,but in what time period ?

Sorry no the new switch was fitted about 3 months ago - I had to get a second electrician a week after the first one as it only worked for a few days - I asked the 2nd to replace the switch but he said it just needed reinstalled. We could get him back around to change the switch but I suspect, given the shower problems we're having, that there is something else wrong. The switch was just stiff - so we left it on rather than keep pulling it really hard.

 

[terryplumb]

Your having electrical problems ,electric switch on shower ,electric ceiling switch ,electric MCB......
You need an electrician !!!

 

[flameport]

We could get him back around to change the switch but I suspect, given the shower problems we're having, that there is something else wrong.

There is definitely something else wrong.
Even if the shower was a 10.5kW model, which would be in the region of 44 or 45 amps, that's still not enough to trip a 40A circuit breaker ever.
To trip a 40A on overload, it would need around 58 amps, and even then it would still require the shower to be switched on continuously for tens of minutes, certainly not immediately.

To trip immediately requires far more current, which would be caused by a fault between L&N or L&E - however a fault between L&E would trip the RCD, so that just leaves a fault between L&N which for some reason is intermittent. That's very likely to be inside the switch, somewhat less likely is a damaged cable or the connections inside the shower itself. All of those need to be checked.

If the switch has overheated before, the cables connected to it will also have overheated causing the copper to soften, and connecting any new switch to that will inevitably result in a loose connection. The cable must be cut back for a decent distance before connecting to a new switch.

 

[MattB83]

There is definitely something else wrong.
Even if the shower was a 10.5kW model, which would be in the region of 44 or 45 amps, that's still not enough to trip a 40A circuit breaker ever.
To trip a 40A on overload, it would need around 58 amps, and even then it would still require the shower to be switched on continuously for tens of minutes, certainly not immediately.

To trip immediately requires far more current, which would be caused by a fault between L&N or L&E - however a fault between L&E would trip the RCD, so that just leaves a fault between L&N which for some reason is intermittent. That's very likely to be inside the switch, somewhat less likely is a damaged cable or the connections inside the shower itself. All of those need to be checked.

If the switch has overheated before, the cables connected to it will also have overheated causing the copper to soften, and connecting any new switch to that will inevitably result in a loose connection. The cable must be cut back for a decent distance before connecting to a new switch.

Thank you - very helpful

 

[MattB83]

Your having electrical problems ,electric switch on shower ,electric ceiling switch ,electric MCB......
You need an electrician !!!

When you say it like that...

I guess the issue might be that we decide to go with running a shower straight off the boiler if that's a viable option in which case we'd get a plumber - rather than get a replacement electric shower.

The other issue I've found when I was replacing the washing machine this week was that the stop cock doesn't completely stop the water so I think I need a plumber before the electrician can do much in terms of replacing the shower.

We've spent a fortune on getting the electrics sorted in this house after numerous faults so I'm just a bit p***ed off with it all at the moment!

 

[terryplumb]

You must endeavour to persevere !!
As the electric shower only takes a mains cold feed , changing to a shower valve , involves ....hot feed would need to be plumbed to the shower valve position. If you have a gravity fed plumbing system the cold would also need to be run from storage ,not cold mains. So quite a bit to it .

 

[MattB83]

You must endeavour to persevere !!
As the electric shower only takes a mains cold feed a hot feed would need to be plumbed to the shower valve position. If you have a gravity fed plumbing system the cold would also need to be run from storage ,not cold mains. So quite a bit to it .

The other complication is that the stop cock doesn't stop the water completely (I remembered this as I got soaked changing a washing machine this week) so we will need a plumber out anyway. It is a coincidence that 2 appliances are tripping the power - but it was an old washing machine and the shower issue has happened before so I'm not reading too much into it.

I didn't realise the cold would have to be run from storage although I'm not sure of our setup - there is a tank in the loft.

 

[terryplumb]

Depends on your plumbing set up. Do you have a combi boiler ?

 

[endecotp]

To trip immediately requires far more current

But it doesn’t trip immediately - it trips “sometimes”, when his wife has a very long shower.

 

[securespark]

Most switches have one screw per terminal, which IMO is not the best for a high-current switch. Click make a 50A shower switch that has two screws per terminal. Much better for making a sound electrical connection.

 

[JohnW2]

... 44 or 45 amps, that's still not enough to trip a 40A circuit breaker ever.
To trip a 40A on overload, it would need around 58 amps, and even then it would still require the shower to be switched on continuously for tens of minutes, certainly not immediately.

As I wrote earlier an MCB is required not to trip below 1.13*In (hence 45.2 for a 40A one), so it wouldn't be impossible if it tripped at any current above that - although,, as you say, if not much above it might take a good while to trip.

To trip immediately requires far more current, which would be caused by a fault between L&N or L&E

True, but 'tripping immediately' seems definitely NOT what the OP is experiencing...

.... However it's still tripping the power occasionally - typically when my wife has has a long and (very) hot shower - has never tripped during my quick warm showers.

I have to say that, particularly if it really is a "9.5 kW" shower, I'm coming to think that a "trigger-happy MCB' might be the most likely explanation.

Kind Regards, John

 

[winston1]

The switch was just stiff - so we left it on rather than keep pulling it really hard.

It is not meant to be turned on and off regularly anyway. It is for isolation on the odd occasions the shower needs to be worked on.

There is no requirement to have one anyway.

 

[MattB83]

Depends on your plumbing set up. Do you have a combi boiler ?

Yes - combi boiler.

 

[MattB83]

As I wrote earlier an MCB is required not to trip below 1.13*In (hence 45.2 for a 40A one), so it wouldn't be impossible if it tripped at any current above that - although,, as you say, if not much above it might take a good while to trip.
True, but 'tripping immediately' seems definitely NOT what the OP is experiencing...
I have to say that, particularly if it really is a "9.5 kW" shower, I'm coming to think that a "trigger-happy MCB' might be the most likely explanation.

Kind Regards, John

Thanks John - I hope that is the case. Although I'm wondering if the fact that it blew a few fuses on the old board suggests something else. I just remembered that when we first moved in (not meaning to drip feed info) the shower fuse had been 'supplemented' with some fuse wire - so perhaps the shower had been causing problems a while back - saying that the fuse had only gone 4 or 5 times in 2 years so not very regularly.