Why do my bathroom light switches keep failing?

[sammy7boy]

Hi folks this is my first post on this forum. I have no electrician qualifications but i DO have a degree in physics and know about electricity: i'm a teacher and teach GCSE and A-level students about current, voltage, power, resistance, resistivity, DC, AC, frequency, electromotive force, kirchhoff's laws, internal resistance, potential divider circuits blah blah blah.

Despite this, I am completely and utterly dumbfounded and baffled by my bathroom light switch situation! I've had five bathroom light switches fail on me in almost as many months and need to install a sixth! I've now tried almost every brand/model of 1-way pull cord switch in the Screwfix catalogue, including MK and Crabtree, and they've all died exactly the same death. They work fine for a few weeks, then they get sick: you need to tug the cord two or three times to switch the lights on. Finally, they die a death, and no amount of pulling can switch on the lights. You replace the switch (with a different brand of light switch just in case) but it follows exactly the same ill-fated life as the last.

This time I decided to open up the switch mechanism of the dead Light Switch the Fifth to investigate what had happened. No dust or anything inside. No corrosion on the contacts. No water or damp. The switch is on a circuit that's powering six 4W LED spotlights and an extractor fan (of around 20W i guess) so the switch should only have a measly 0.2A of current flowing through it - miles below its current rating. The bathroom is not particularly humid and during the summer months the window is open pretty much all the time anyway. There is no damp or anything else untoward on the plaster of the ceiling where the switch is screwed into.

So i'm completely out of ideas. The cause might be something really obvious, but it's certainly not anything that i or my stepdad (who's a retired design & technology technician) have been able to figure out.

Please, if anyone else has experienced this issue and knows what the problem is i'd love to hear from you, because right now i'm the dark.

Thanks, Sam :smile5:

 

[markc123]

Hi Sam ... Wow, lol.

By dead do you mean the pull chord won't operate and nothing else? Have you used a voltage tester to make sure there is still power present at the switch?

If it's literally just the pull chord refusing to pull, dare i say you might be the 'hulk' and not realise it. I.e. you're breaking them by pulling too hard. Is the switch being used as a junction box? by this i mean, does it have quite a few wires in it, I'm thinking maybe pressure is causing the chord to fail after a while - although this is unheard of to me.

You're either been a heavy handed bugger lol

or,

Ermmmm - extreme bad luck lol?

Sorry to not be of help, but in all honesty i have really no idea lol.

Mark.

 

[telectrix]

seems like mechanical failure of the mechanism rather than an electrical problem. kids are usually the cause. tugging too hard on the cord.

 

[Spoon]

Hi Sammy. Welcome to the forum.
I think markc could be right in his post.
You do say that you have opened up the switch and there is 'No dust or anything inside. No corrosion on the contacts. No water or damp.' So it sounds like the pulley mechanism has gone faulty. When you have opened it up do the contacts engage when you pull the cord?

looks like tel beat me to it. I really need to stop being distracted when typing a post.

 

[sammy7boy]

Thanks for the replies. There's definitely a voltage across. I agree that the fault is likely mechanism related, but no one around here has been breaking switches by pulling too hard. Our two-year-old is too little to reach the cord and we've both been pulling cord switches in the same way for thirty odd years and never experienced this before. It makes no sense to me that five switches all of different manufacturers should break in exactly the same way in as many months. A decent switch should last decades. I must admit that is the first time i've tried to open up the mechanism itself to investigate, so, once i've figured out where all the bits and pieces that fell out go back i can start to explore the workings of the mechanism itself to see what the heck is happening. Right now i'd say that the most logical explanation is that our bathroom is haunted.

 

[Spoon]

If everything is ok with the contacts then it most probably is the mechanical pull mechanism that has gone faulty, as I said in my previous post. I presume you have replaced it with another pull switch? Ever thought of replacing the pull switch with a switch on the outside of the bathroom?

 

[markc123]

our bathroom is haunted.

They don't make things like they used to though mate, i still think along with the other's, they're being pulled too hard.

However, I'm happy to go with your suggestion as well - you've got a really strong ghost in your house.

 

[Spoon]

you've got a really strong ghost in your house.

You've seen the film Poltergeist. They can do some damage....

 

[Guest77]

Hi folks this is my first post on this forum. I have no electrician qualifications but i DO have a degree in physics and know about electricity: i'm a teacher and teach GCSE and A-level students about current, voltage, power, resistance, resistivity, DC, AC, frequency, electromotive force, kirchhoff's laws, internal resistance, potential divider circuits blah blah blah.

Despite this, I am completely and utterly dumbfounded and baffled by my bathroom light switch situation! I've had five bathroom light switches fail on me in almost as many months and need to install a sixth! I've now tried almost every brand/model of 1-way pull cord switch in the Screwfix catalogue, including MK and Crabtree, and they've all died exactly the same death. They work fine for a few weeks, then they get sick: you need to tug the cord two or three times to switch the lights on. Finally, they die a death, and no amount of pulling can switch on the lights. You replace the switch (with a different brand of light switch just in case) but it follows exactly the same ill-fated life as the last.

This time I decided to open up the switch mechanism of the dead Light Switch the Fifth to investigate what had happened. No dust or anything inside. No corrosion on the contacts. No water or damp. The switch is on a circuit that's powering six 4W LED spotlights and an extractor fan (of around 20W i guess) so the switch should only have a measly 0.2A of current flowing through it - miles below its current rating. The bathroom is not particularly humid and during the summer months the window is open pretty much all the time anyway. There is no damp or anything else untoward on the plaster of the ceiling where the switch is screwed into.

So i'm completely out of ideas. The cause might be something really obvious, but it's certainly not anything that i or my stepdad (who's a retired design & technology technician) have been able to figure out.

Please, if anyone else has experienced this issue and knows what the problem is i'd love to hear from you, because right now i'm the dark.

Thanks, Sam :smile5:

Why does your bathroom switches keep failing then? chuckle

 

[Sintra]

The cold start up current for LED lamps can be x100's of the running current. For example a job I was doing had 30 watts of LED load but the cold start up for this small load was 40A. What I'm getting at is this initial start up current might be enough to damage the contacts within your switch especially if your switch is only rated for 6A as most pull cords are. If it was me I would try a 20A pull cord and see how that goes.

 

[Guest77]

One thing I have come across in my time Sammy is if the cables are too long or the pattrice too shallow then a strain can be put on the actual mechanism which will cause it to break after a period of time, my advice is to check the cable length or use a deeper pattrice.

 

[sammy7boy]

I told my missus that people think that we've been pulling the cord too hard and she disagrees. And believe me, you don't want to get on the wrong side of her. I promise that we've both lived in lots of different houses during our lives and never ever broken pull cord switches before. And i promise that neither of us suddenly changed our pull "style" to karate chop. Yes i've replaced with whole new switches every time. Just playing with the mechanism of the current (5th) broken switch. You pull it and most the time you hear that satisfying click sound but occasionally it feels like it "gets stuck" and doesn't complete the click. This is exactly the same issue as i've had with all the other switches i've tried over the last few months. Excluding the idea that they're being pulled to hard, then if no one can explain why they all keep breaking, i guess i've just got to accept that maybe i've been unlucky. Exceptionally unlucky. Just because there's a million-to-one chance of moving into a house and the light switch breaking after a few months so you replace it with a cheapo unbranded Screwfix switch, then a Crabtree switch, then another Crabtree switch, then an MK switch; each time the switch mechanism inexplicably failing in the same way after a few weeks of "normal" usage. Just because it's extremely unlikely that this should happen, it doesn't mean that it couldn't. I suppose there's nothing else for it other than to pop down to the shop and buy a sixth switch. Maybe i could move the switch to outside the bathroom - i do, after all, enjoy being able to stand on the landing and switch the lights off on someone in the bathroom after they've pee'd me off - but i can't say i'm really sure what difference it would make. Plus it's a rental property and i can be bothered with the agro of getting permission and then filling/sanding/painting the old hole. Maybe if i bought the most expensive 1-way pull cord switch that money can buy then it might not break?

 

[Guest77]

The cold start up current for LED lamps can be x100's of the running current. For example a job I was doing had 30 watts of LED load but the cold start up for this small load was 40A. What I'm getting at is this initial start up current might be enough to damage the contacts within your switch especially if your switch is only rated for 6A as most pull cords are. If it was me I would try a 20A pull cord and see how that goes.

yes that is actually a very good point Bud, I never thought about that but you are quite right.

 

[sammy7boy]

MDJ - maybe you're right! Cables do look a bit long and it is a bit of a squeeze to get it all back together. Maybe i'll try trimming them down and seeing what difference it makes. Cheers

 

[Guest77]

MDJ - maybe you're right! Cables do look a bit long and it is a bit of a squeeze to get it all back together. Maybe i'll try trimming them down and seeing what difference it makes. Cheers

After your reply I am certain that is the problem, you need to get those cables into the back of the box away from the actual switch mate, a deeper box would be an advantage as well.