10.5kw shower

[elliot123]

Yesterday smelt a weird smell of burning/melted plastic in my bathroom after some looking about realised was the shower pull cord opened it to the the incoming live insulation completely melted an charred and the pull cord terminal melted shower was installed about 3/4 years ago but recent board change by council(council house), I've done a cable calc and l got a Ib of 45.65 A so next suitable breaker 50A and got a 10mm t&e, currently on 6mm 40A breaker. Would you reckon this was the reason it had melted or due to other reason?

Ps have isolated removed switch and stopped using shower

 

[Edd]

It would have melted due to loose conection or dirty contact at pull switch.

 

[elliot123]

But has wrong size mcb and cable? According to my cable calc

And no loose screws when I took pull cord off?

 

[loop3]

Agreed. More then likely a loose. But cable is the wrong size any how.

 

[telectrix]

depends on the installation method. 6mm method C is 47A.

 

[Edd]

It is the wrong size cable for a 10.5kw shower, and yes it really should be 10mm on a 50A mcb. but none of that would have melted the terminal at the pull switch.

 

[elliot123]

It is method C comes up threw void under airing cupboard then clipped in airing cupboard only bout 3 or 4 metre run but then still being 47 A wouldn't it be 50a breaker required? And 10mm

 

[elliot123]

Could it of anything to do with being in the bathroom? Was a slight bit of moisture on the switch but more sticky so fought from the melting cable?

 

[telectrix]

no, In < Iz. so that the MCB trips before the cable is overloaded. so if Izis 47A, then a MCB below 47A In is selected.

 

[telectrix]

you get a little warmth at the terminations in the switch due to load current. this leads to expansion/contraction leading to a slightly loose connection after time. this then starts to arc, burn, and before you know it here comes fireman sam with his hose.

 

[elliot123]

So what would you suggest to do? Replace cable? Replace breaker? Currently 6mm and 40a breaker ?

 

[malcolmsanford]

To be honest I doubt that a 6mm cable would have melted on a 45/50 amp supply unless the cable was sub standard and there have been cases of that.

More likely the switch had melted due to

a) Loose connection
b) Moisture getting into it and shorting
c) Cheap and nasty accessory ( same as cable could have been)
d) Old accessory that was rated 45amp and finally broke down

 

[elliot123]

Pull cord is rated at 45a and breaker 40a.

So what is the best thing for me to do? Upgrade cable and breaker ?

 

[telectrix]

the 40A breaker will protect the 6mm from overload. start off by replacing the switch for a good quality one, crabtree round ones have good reports. then with the shower going full heat, clamp the L core in the DB and see what it's drawing. i'll be surprised if it's > 40A.

 

[malcolmsanford]

Change the switch to the 50amp Crabtree type, if the cable got damaged then you may have to replace, but you can IR test it ............if not damaged then just replace the switch.