Shower pull cords

[sparkwright]

Inspired by a recent topic on Wylex main switches, I thought we could discuss 40-50 amp dp pull cord switches, typically for showers.

One question has to be - Do they burn out solely because the terminals aren't tightened/copper wire isn't clean and shiny?

Or are they badly made inside?

I remember fitting a cheap one once and I KNOW I tightened everything up as I was checking all the time I was offering the faceplate to the back box. It burnt out three years later. The MK replacement has lasted 7 years so far to my knowledge.

Another question is WHY are these things so bad? WHY hasn't anyone done anything to improve these?

Another problem with these things is the pull cord can jamn up, or the cord has to be pulled several times before they function.

As you all probably know, only the round Crabtree ones seem to be any good.

 

[securespark]

Me and my Mum both have MK 2G sized 45A wall switches outside. Hers is 1986 vintage Logic with two sets of screws per terminal wired in 10 milli (yes, it cost an arm and several legs back then), mine 1999 vintage Logic Plus wired in 6 milli.

Both have lasted all that time without degradation with 8.5-9.5kW showers on them.

 

[winston1]

Don't operate them under load. Better still, don't operate them at all except when you need to isolate the shower for maintenance. There is no need to isolate after every shower.

 

[Steve]

Don't operate them under load. Better still, don't operate them at all except when you need to isolate the shower for maintenance. There is no need to isolate after every shower.

But operating the switch is not what causes them to burn out. At least not in the context of this thread.

 

[bernardgreen]

Don't operate them under load. Better still, don't operate them at all except when you need to isolate the shower for maintenance. There is no need to isolate after every shower.

But operating the switch is not what causes them to burn out. At least not in the context of this thread.

Operatimg any mechanical switch under load will cause wear and tear on the contact surfaces and as a result the contact resistance increases. Eventually the the contact resistance becomes high enough to cause significant heating of the contact area which then accelerates the wear and tear of the contact faces. Eventually the degredation of the contact area increases contact resistance to the point that the heat generated in the contact area is enough to affect the whole switch mechanism and terminal.

 

[EFLImpudence]

Surely that would cause the same damage to both pole contacts or, at least, 50-50 over time.
Why is it usually the Neutral which overheats?


Do people operate them under load?
That would mean stepping out of the shower while it is still on instead of pressing a little button or turning a knob to turn it off.

If Crabtree's don't burn out, the others must just be rubbish.

 

[bernardgreen]

Invariably one contact operates milliseconds before the other and that one takes the brunt of the wear and tear.

Is it really true that it is usually the Neutral ? I have seen / replaced a few with scorched Live coductors.

A couple of people I know use the cord rather that touch the switch on the shower unit.

 

[EFLImpudence]

In my experience it is usually the neutral - and with immersion timers which only switch the line.

Fair enough if you know people who use the the cord but they should not do that as the shower usually 'runs down' before completely switching itself off.

 

[bernardgreen]

Fair enough if you know people who use the the cord but they should not do that as the shower usually 'runs down' before completely switching itself off

I have explained that itis better to use the switch on the shower but they have this "phobia" about water and electricity. It is irrational to be fearful of touching the switch button when they may be holding the shower hose with the power on.

 

[winston1]

I have explained that itis better to use the switch on the shower but they have this "phobia" about water and electricity.

In that case why do they use an electric shower at all?

 

[bernardgreen]

Winston messed up the quoting

I have explained that itis better to use the switch on the shower but they have this "phobia" about water and electricity.

In that case why do they use an electric shower at all?

Because they do not have gas to their properties so have to have electric heated showers.