Damaged Shower Isolator Switch

[PhilP2]

Hi, recently my shower isolator pull switch failed to turn off. On examining the switch it was evident that it had over heated damaging the insulation of the wires going to the terminals. I have replaced the switch with an MK 45A switch but I am concerned about the wiring; the damage is slight, charring about 1 – 2 inches up from the terminals. Do I need to replace the complete cable back to the CU and forward to the shower unit or can I use a couple of inline junction boxes and some new cable. The other concern is that my current wiring is Pre-2004 (red/black/earth) and I’m not sure if it can be mixed with the modern (brown/blue/earth).

 

[JohnD]

This quite common. It usually happens when one of the terminals is not tightened enough. The loose connection heats up, expands and contracts, gets looser, becomes high-resistance and overheats more and more and burns away the copper, becomes looser, etc. It is particularly common on shower circuits because they run at high currents for long enough to get hot.

You have to cut away all the heat-damaged insulation and the dark copper to clean and bright. If there is not enough slack the cable can be extended but the cost of the correct tool, plus the skill to make a good joint, means it will often be better value to get a well-recommended qualified local electrician in. If you were to use junction boxes they would have to be extremely large high-current ones, preferably with two screws for each core, which would add to the cost. The common ones found in hardware stores are not adequate. Screwed connections have to be accessible for inspection and maintenance to guard against the very problem you have just found.

Large sizes of terminals need to be retightened after a few days because the softish copper squashes to shape under the screws.

 

[PhilP2]

Thanks very much for that, I dont think there is enough slack in the cable for me to rectify this fault and I think with the inherent dangers of a job like this I will leave it upto a professional.

Your advice is much appreciated.

 

[ban-all-sheds]

If you were to use junction boxes they would have to be extremely large high-current ones, preferably with two screws for each core, which would add to the cost.

 

[JohnD]

is that the half-inch one, or the six-inch one?

 

[kai]

I think shower pull switches should be banned, the design is not fit for purpose (as thousands of posts on this site and others have implied), Using a 50amp Wall mounted switch outside the bathroom seems a safer solution.

It appears that an inherent weakness in the design of shower pull switches makes them a potentially dangerous choice.

 

[Adam_151]

I think shower pull switches should be banned, the design is not fit for purpose (as thousands of posts on this site and others have implied), Using a 50amp Wall mounted switch outside the bathroom seems a safer solution.

Nonsense!. A decent make of switch, terminated correctly will not fail.

 

[ban-all-sheds]

I've had an MK in my bathroom which is operated ON/OFF at least once a day, sometimes 3 times, for 8 years.

 

[RF Lighting]

What should be banned is limp wristed people who can't manage to terminate a domestic accessory properly.

It's not just shower switches that get left like this, just they are most common to fail due to the current running through them.