Pull cord switch for power shower keeps breaking

[MalcolmS]

Hi All,
I hope you are doing well.
I keep having the issue with this pull cord switch to the power shower.
I used a number of pull cord switches 45A and 50A ones mostly from Screwfix but I think the problem is with the wiring.
As you can see on the picture the RED and BLACK twisted copper wire keeps burning and this eventually kills the switch.




I have shortened it already but IMHO these RED/BLACK wires are unmanageable and continue burning.
These twisted copper wires are so hard when you screw all the wires I have to use a lot of force to push the switch into the plastic box.
What would you suggest to do?
Should these wires be completely changed?

I could also get rid of the switch permanently but then the switch on the power shower is also gone and I cannot get a replacement (the manufacturer changes the orientation of the switch inside the power shower to force to go for a new shower).
This shower and the electrical work has been done about 8-10 years ago and it's due for some maintenance but I am not the owner and the place is for sale so I am keen on good temporary solution rather than a complete work.
Best regards

 

[littlespark]

Even in the short term, the pull cord has to be replaced so there is local isolation for the shower.

They’ve never been a good design, and totally agree that it’s a squeeze to get all the cables into the switch, and screw the switch up.
This causing cables forced into the wrong place, and terminals becoming slack and resulting in overheating.

A lot of times the pull cord is pulled too hard which damages the inner workings.

Ideally, a 45 or 50A wall switch that uses a deep 2 gang box gives more space to work with.

 

[johntheo]

Maybe its the photo but it looks like the connector block is too big and if so the terminal screws can just pinch the sides of the cable to give a very poor connection.

 

[Marvo]

There's numerous reasons that cause burned terminations, this is just some of them;

• Damage to the copper conductors when the wires are stripped of their insulation.
• Tight twisting of the copper strands with linesmans pliers before the connection is made. Rather use a bootlace ferrule.
• Undertightened screws. Causes loose connections.
• Overtightened screws. Causes the strands of the wire to be partially or fully cut. Use a bootlace ferrule to prevent this and use cage clamp type connectors or the ones with an internal tongue to prevent the end of the screw contacting the wire strands.
• Incorrectly sized or just poor quality connectors. I've seen cheap connector blocks with steel screws with razor sharp edges that cut the wire even when moderately tightened. Again, use a bootlace ferrule. Also giving the wire a 'haircut' to make it fit in the connector is a fairly common problem.
• Counterfit wire which isn't pure copper or may be undersized. Not very likely.
• Very tight bend at the connection point. The copper strands on the outside of the bend get stretched which reduces their diameter and current carrying capacity. Quite likely with the lack of space in a pull switch.

Connector block with wire protection tongue.

 

[johntheo]

The 9kw (15 year old) Mira Sport shower I have has those tongues on the end of the screws but the connector block was supplied with the shower.

 

[MalcolmS]

Hi Gentlemen,
These burns are old ones before I used the above connector, it burnt while a number of pull cord switches have been replaced over the years. I cut the burnt end a couple of times but I am worried I eventually run out of wire.
But it make sense thanks to @Marvo to use bootlace ferrule to prevent burning.
My other concern is to put this back in the plastic enclosure without severing the wire contacts. As I said I have to push it hard to fit into the plastic box and I think this results in some of these wires becoming lose then create the resistance burn wire and perhaps damage the switch itself.
I think @littlespark is right and with the new switch I am going to make the pull cord half the length to prevent people from pulling it too hard.

 

[johntheo]

It would be interesting if you could measure the voltage drop (if any) across the terminal block with shower in use.
Also wonder if the isolating switch which is sometimes located outside the bathroom door fails as regularly.
Its also said that these isolation switches are for maintenance purposes. if so, why isolate the supply each time one leaves the shower?, the actual switching inside the shower is done when the solenoid switch when pressed supplies water pressure to the flow switch and its this (differential) pressure that closes the micro switches to power the heating elements.

 

[MalcolmS]

It would be interesting if you could measure the voltage drop (if any) across the terminal block with shower in use.
Also wonder if the isolating switch which is sometimes located outside the bathroom door fails as regularly.
Its also said that these isolation switches are for maintenance purposes. if so, why isolate the supply each time one leaves the shower?, the actual switching inside the shower is done when the solenoid switch when pressed supplies water pressure to the flow switch and its this (differential) pressure that closes the micro switches to power the heating elements.

I have not measure the voltage but yes there is another switch outside the bathroom for the shower but this one is regular on/off switch and so far it didn't break.
The press switch in the shower is broken and I could not get a replacement as the maker changed the switch not to fit this old shower.

 

[johntheo]

I have not measure the voltage but yes there is another switch outside the bathroom for the shower but this one is regular on/off switch and so far it didn't break.
The press switch in the shower is broken and I could not get a replacement as the maker changed the switch not to fit this old shower.

So, you are using the pull cord isolator to start/stop the shower??. starting the shower won't have any effect on the pull cord contacts because there will be a delay between these closing and the shower contacts closing but the isolator contacts are breaking the shower current of 40A if used in this manner.

 

[MalcolmS]

So, you are using the pull cord isolator to start/stop the shower??. starting the shower won't have any effect on the pull cord contacts because there will be a delay between these closing and the shower contacts closing but the isolator contacts are breaking the shower current of 40A if used in this manner.

Yes, at the moment yes. Does it mean the shower is going to break sooner than later if I continue doing that?

 

[johntheo]

Yes, at the moment yes. Does it mean the shower is going to break sooner than later if I continue doing that?

Don't think it will have any effect on the shower life, don't really know about the isolator contacts, and don't know if it had/has any part to play in the burnt wiring if it has been going on for a long period, whatever about the contacts one would think that it shouldn't have had any effect on the wiring.