Shower tripping MCB

Rosspropertymaintenance · 8 Mar 2013

Hiya...new here
Today's client had a Triton Spellbind 10kw that worked fine for about 5 mins but would then trip the MCB, flick it back on, try the shower again and it would run perfect for 5 mins then trip again.
I guessed at an overheat stat, any idea's ?
Is wired up with 10mm cable.
Many thanks for any pointers.
Ross

JohnD · 8 Mar 2013

the rating (kW) of the shower is 10kW

what is the rating (A) of the MCB?

ericmark · 8 Mar 2013

10kW = 43.5A but often they will run from a B32 MCB. However over time the MCB degrades and the time before they trip slowly gets shorter and shorter. I have also had where the occupants knew they had to run on low only then new occupants arrive and trouble starts.

Rosspropertymaintenance · 8 Mar 2013

Many thanks for the replies guys.
As a plumber (with limited electrical knowledge) I didn't note the rating of the MCB so will get the client to check and let me know,I had assumed the problem would be within the shower unit....(& we all know what happens when you Ass U me, eh !)
That would make sense as the time between tripping (according to the client) does get shorter if repeated showers are taken.
I really hope she replies saying it's a 32 amp, would just fitting a new 32amp MCB do the job or do you suggest upgrading to a new 45 amp ?
Rossy

flameport · 8 Mar 2013

A 32A MCB is wrong, replacing it will do nothing.

A 45A MCB could be used, provided the cable is the correct size and not installed in such a way as to reduce it's capacity.
However, the cable in this picture does NOT look like 10mm, as the black & red wires in the cable appear to be thinner than the blue & brown wires in the shower itself.

Untitled

If the cable is 6mm as it appears, the options are
replace the shower with a lower rated item, a 7kW would be fine.
replace all of the cable from the consumer unit to the shower and fit a higher rated MCB
ditch the electric shower and fit a proper one.

Rosspropertymaintenance · 8 Mar 2013

Looks like I'd best go back to the property and take another look....
If I am correct....6mm feed cable will be a solid core, 10mm feed will be stranded ?
I am not sure who fitted the unit but I do know it was done fairly recently as when I fitted the suite there was no electric shower at all. It worked fine with just a bath/shower mixer tap, the property is a 4 storey town house and as this bathroom is in the basement there was no problem with water pressure from tank fed system, they removed the nice bath shower mixer and fitted just a bath mixer/ filler & a mains fed electric shower- daft !
Rossy

flameport · 8 Mar 2013

6mm usually has a solid cpc (earth) with the other cores stranded, 10mm will have a stranded cpc.
However some older cables had stranded cores in smaller sizes, so the presence of a stranded cpc isn't a 100% method of determining cable size.

There is a list of actual outer dimensions for various cables here:
//www.diynot.com/wiki/electrics:cable_types:flatpvccables

It's also somewhat concerning to note that this was installed recently, as cables with black & red cores were replaced with blue & brown ones 7+ years ago.

JohnD · 8 Mar 2013

quite a handy way to identify T&E sizes is to keep a few sample cable clips in your toolbox to fit 1mm, 1.5mm, 2.5mm, 4mm, 6mm, 10mm and 16mm. They will be a snug fit on the correct cable.

I seldom come across 4mm and 1mm.

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Shower tripping MCB

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