Replacing an electric shower

[enknt]

Hi,

I'll start off by saying that I haven't got any electrical experience at all.

I recently moved into a house that had an electrical shower installed.

It needs replacing, but because the plumbing etc is already there for the old shower, I was going to fit it myself.

The electrical cable going to the shower is concealed within the wall the shower's mounted on (the wall's then been tiled).

It looks like when the old shower was wired in, the wires that were sticking out of the wall to be connected to the shower weren't long enough so they've been extended by about 4" by using terminal blocks & bits of cable.

These wires & the terminal block have melted when the shower failed, but if I just cut the melted bits off these wires then the remaining cable length sticking out of the wall is not going to be long enough to connect to the new shower.

What's the best way of making this cable long enough?

My initial thought is to remove some of the tiles from the wall, remove bits of the plaster from the wall, dig about a 2 foot length of the cable out of the wall, cut off about a foot and a half of it, extend it so it'll be long enough to fit the shower then re-plaser/tile over the top.

I thought by doing this the joint where the cable's extended is buried deep inside the wall.

Does this sound like a reasonable idea & within the reach of someone with next to no electrical knowledge or should I just get someone in to do it?

If so what's the best way of joining the extention bit of cable to the original cable bearing in mind it'll be plastered over?

If it sounds like a rubbish idea, any ideas for a way I can do it would be appreciated!

 

[Steve]

you need to rip that cable out back to the shower switch (usually on the ceiling) and replace the entire length. This join was done badly, terminal blocks are not the way to extend cable that could carry 50 amps. They should have been crimped.

The shower failing almost certainly did not cause this melting you describe - it was a bad joint or incorrectly rated terminal blocks that caused the melting, over a long period of time.

While you have the shower switch open, check the supply cable from the consumer unit. If it is showing signs of damage, the wrong size cable may have been used. Get an electrician to inspect this if this is the case.

EDIT out of interest, what symptoms did you get that told you the shower was knackered? i only ask because there may, in fact, be nothing wrong with it, it may just be this bad join that stopped it working

 

[plugwash]

you need to rip that cable out back to the shower switch (usually on the ceiling) and replace the entire length. This join was done badly, terminal blocks are not the way to extend cable that could carry 50 amps. They should have been crimped.

you can get 60A rated chock block ofc that doesn't mean he used it

The shower failing almost certainly did not cause this melting you describe - it was a bad joint or incorrectly rated terminal blocks that caused the melting, over a long period of time.

yeah i'd probablly agree with you there

While you have the shower switch open, check the supply cable from the consumer unit. If it is showing signs of damage, the wrong size cable may have been used. Get an electrician to inspect this if this is the case.

even if there is no damage you still need to check the cuircuit it suitable for the load up put on it.

if the cable is 10mm it would be possible to do a decent in wall joint but by no means trivial (10mm uninsulated crimps followed by adhesive heatshrink over the individual joins followed by adhesive lined heatshrink over the whole lot), probablly easier to replace the whole length to the switch.

if the cable is 6mm the jointing would be slightly easier as you can use insulated crimps BUT you are limited to a pretty wimpy shower and you would probablly wan't to do a new shower cuircuit from scratch.

you also should check out the protective device arrangements at the CU

 

[enknt]

Thanks both of you!

The shower that's fitted is 10.5kW but the cable is only 6mm (!!!!!) so either the shower or the entire cable run needs replacing. It'll be less disruptive to just try fitting a lower power shower so it'll only be drawing 30ish Amps.

In this case do you both think it'll be ok to extend the cable as I described in my original post?

If so then am I looking for any particular type of insulated crimp connectors & do I still need to cover the joint in heatshrink?

If so would putting a single heatshrink tube over the bundle of 3 wires (each joined by an insulated crimp connector) & then plastering it so it's concealed in the wall be ok? And am I looking for any particular type of heatshrink?

Sorry if I seem to be repeating myself a bit but I just want to get it right!

Thanks again!

 

[Steve]

Thanks both of you!

The shower that's fitted is 10.5kW but the cable is only 6mm (!!!!!) so either the shower or the entire cable run needs replacing. It'll be less disruptive to just try fitting a lower power shower so it'll only be drawing 30ish Amps.

In this case do you both think it'll be ok to extend the cable as I described in my original post?

If so then am I looking for any particular type of insulated crimp connectors & do I still need to cover the joint in heatshrink?

If so would putting a single heatshrink tube over the bundle of 3 wires (each joined by an insulated crimp connector) & then plastering it so it's concealed in the wall be ok? And am I looking for any particular type of heatshrink?

Sorry if I seem to be repeating myself a bit but I just want to get it right!

Thanks again!

to only draw 30amps, you need a 7.5kw shower (32amps) but you will get pretty poor flow in winter with this, more of a dribble than a flow.

That cable may be damaged in other places, and without testing insulation you cant be sure (heat may have broken down the insulation inside the cable), so it would be best to replace the whole run of cable back to the consumer unit with 10mm².

If you do crimp it, use a proper ratchet crimper, not the squeeze-n-pray ones used in cars. And you can use insulated crimps, as plugwash said, as it is only 6mm².

 

[ban-all-sheds]

1) I guarantee that if you're used to a 10.5kW shower and you fit a 7.5kW one you will be dreadfully disappointed.

2) Add to that the possibility that the cable is already damaged.

3) Time to bite the bullet and replace the cable...

 

[enknt]

It sounds like you're right, I think I'll get the whole cable replaced!

Thanks, it was worth exploring the possibility of extending the existing cable but it sounds like a bit of a non-starter. I don't want to spend money having a new 7.5kW shower to suit the 6mm cable only to realise it's not good enough & have to spend more on yet another shower (10.5kW this time) AND having a new 10mm cable put in as well!

Thanks for your advice!

 

[plugwash]

If you do crimp it, use a proper ratchet crimper, not the squeeze-n-pray ones used in cars. And you can use insulated crimps, as plugwash said, as it is only 6mm².

you should always maintain at least two layers of insulation so if you use insulated crimps then thats the first layer. The second layer would be heatshrink or possiblly self amalgamating tape covering the whole joint.