Plastic bit on pull cord switches is for insulation/saftey reasons?

[mattylad]

It is a good point though, bathrooms do steam up and a wet cord could possibly be a risk under certain circumstances.
Lots of things have little "it may happen, maybe it wont" features built into them.
Not all pull cords are as well made as the ones your likely thinking of.

 

[JohnW2]

It is a good point though, bathrooms do steam up and a wet cord could possibly be a risk under certain circumstances.

I suppose that depends upon what one regards as 'a good point'. I've never seen one in which the top end of the cord gets anywhere near anything electrical and, even if it did, I suspect that even a soaking wet cord would not have a low enough impedance to be a serious risk.

Lots of things have little "it may happen, maybe it wont" features built into them.

Yes, as we've discussed attitudes to risk ('risk averseness') varies dramatically between individuals, but there is (at least in my opinion) a limit to what is sensible and/or practical. Those who look at "it may happen" from an extreme risk-averse viewpoint are very restricted in what they can do - they certainly couldn't travel in cars, cross roads, go up ladders/steps, use any sort of tools etc. etc.

Some of the "it may happen" things are difficult for even them to avoid. If you look at the statistics, things like going up/down stairs, getting out of bed and 'getting dressed' are each the underlying cause of more UK deaths than are electric shocks. You probably should be having this discussion with bernard.

Kind Regards, John

 

[SUNRAY]

I don't know if this is relevant but I looked at the red and orange assistance calls in sheltered accomodation today while visiting and those I saw are about 50:50 with/without the insulator, these are of course working on SELV.
The bathroom and toilets [that I saw] didn't have them.

Also the insulator was introduced well before 1974.

 

[JohnW2]

I don't know if this is relevant but I looked at the red and orange assistance calls in sheltered accomodation today while visiting and those I saw are about 50:50 with/without the insulator, these are of course working on SELV.

Were these custom-made ('rated') just for SELV? If so, it would obviously be even more ridiculous to talk about 'insulators'. However, I can imagine that, in such environments, there could well be more frequent than usual need/desire to replace the lower parts of the cord.

Also the insulator was introduced well before 1974.

I'm not sure whether I still have any (if I can find one, I'll post a piccie) but I certainly used to have some in which the so-called 'insulator' was made of brass. This 'cord connector' was hollow and made in two parts which screwed together, with holes in the two ends. One inserted one of the cords through each hole, tied a 'double knot' near the end to stop it coming out, and then screwed the two brass parts (each with an attached cord) together ... which I would think rather puts paid to some of the suggestions we're hearing as to why they were introduced

Kind Regards, John

 

[SUNRAY]

Were these custom-made ('rated') just for SELV? If so, it would obviously be even more ridiculous to talk about 'insulators'. However, I can imagine that, in such environments, there could well be more frequent than usual need/desire to replace the lower parts of the cord.

They are non latching so certainly not the 'standard product.

I'm not sure whether I still have any (if I can find one, I'll post a piccie) but I certainly used to have some in which the so-called 'insulator' was made of brass. This 'cord connector' was hollow and made in two parts which screwed together, with holes in the two ends. One inserted one of the cords through each hole, tied a 'double knot' near the end to stop it coming out, and then screwed the two brass parts (each with an attached cord) together ... which I would think rather puts paid to some of the suggestions we're hearing as to why they were introduced

Kind Regards, John

Yes you are correct, they were phased out many decades ago and initially replaced with a plastic clone of that arrangement. My gut feeling tells me I should have samples of as one of the BT duties was to replace the cords in exchanges when they broke, as such I tended to keep several in my tool box and I also found them handy for a smaller knob. They too were phased out [as there was nothing to stopp the 2 strings touching] in favour of the current version with 2 distinct cavities. Also the first of the current versions had the openings on oposite sides to keep the strings apart.

 

[JohnW2]

Yes you are correct, they were phased out many decades ago and initially replaced with a plastic clone of that arrangement.

We know manufacturers. I'm sure that a tiny plastic moulding is much easier/quicker/cheaper to make than two machined brass components

Of course, over the decades many/most of things electrical (enclosures, accessories etc.) which were once metal have gradually changed to being plastic, and I don't doubt that, in addition to cheapness of manufacture, another reason has been the belief that non-conductive materials were generally 'safer' - until, that is, the LFB forced us back into the dark ages!

My gut feeling tells me I should have samples of ....

As I said, same here (but for different reasons), but goodness knows where!

Kind Regards, John

 

[Adam_151]

I looked at a few of these yesterday where I was working and most had the plastic bit so small that the two knots touched together, I would think if they were for a safety purpose then they'd certainly be longer to prevent this and to migitgate againt a path forming on the outside due to condensed droplets. The instructions would contain a warning about not tying the ends together if it breaks (I've never seen this anywhere).

I firmly believe that this is a story that has formed somehow, and because it sounds somewhat credible it has propogated, I'm more inclined to belive it came about not just for use convieince (in case of a snapped string) but also a manufacturing convienience... the process that produces the switch body probably doesn't want to contend with a mass of string, so this gets attached later on

I would imagine the string is atatched inside to a plastic component anyway, so even if the complete string were sodden then there wouldn't actually be a problem

 

[bernardgreen]

but also a manufacturing convienience...

good one,

 

[Harry Bloomfield]

I firmly believe that this is a story that has formed somehow, and because it sounds somewhat credible it has propogated, I'm more inclined to belive it came about not just for use convieince (in case of a snapped string) but also a manufacturing convienience... the process that produces the switch body probably doesn't want to contend with a mass of string, so this gets attached later on

I would agree with that as the correct explanation, followed by them being much later modified so as to easily snap, to prevent kids hanging themselves on the cord playing.

 

[aptsys]

I'm amazed this discussion is still going on. The electrical isolation is afforded by the switch itself, not the cord.

 

[Harry Bloomfield]

I'm amazed this discussion is still going on. The electrical isolation is afforded by the switch itself, not the cord.

Nowt much wrong with a lengthy and interesting technical discussion.

 

[EFLImpudence]

I think Sunray is winding up everyone.

 

[aptsys]

Nowt much wrong with a lengthy and interesting technical discussion.

Most of this isn't technical

 

[SUNRAY]

I'm amazed this discussion is still going on. The electrical isolation is afforded by the switch itself, not the cord.

I think Sunray is winding up everyone.

I'm amazed that there only seems to be 2 people who are aware of the history of these things and this is genuinly no wind up.

I've asked a few colleagues and one didn't even realise that all regular pull switches have them.

 

[EFLImpudence]

Then it must be another urban myth or old wives' tale.