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Replacing a single pole switch


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I need to replace a single pole on/off switch on the boat. The old one is a standard plastic light switch like you get in a house, that simply bridges the positive 12v feed to a pump to isolate it. However the replacement that I have has a metal finish not plastic. The packaging says that because it's metal, the switch frontplate must be earthed. And it says that, "all earth terminals provided must be connected to the protective earth conductor". But the old switch only has two positive cables running to it and nothing else. ?

 

So... do I need to run a negative cable to the switch to provide the earth connection? Or do something else, so that I don't get turned into a delicious bacony Frazzle when I use the switch? ?

 

 

 

20201208_202437_resized.jpg

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3 minutes ago, BlueStringPudding said:

I need to replace a single pole on/off switch on the boat. The old one is a standard plastic light switch like you get in a house, that simply bridges the positive 12v feed to a pump to isolate it. However the replacement that I have has a metal finish not plastic. The packaging says that because it's metal, the switch frontplate must be earthed. And it says that, "all earth terminals provided must be connected to the protective earth conductor". But the old switch only has two positive cables running to it and nothing else. ?

 

So... do I need to run a negative cable to the switch to provide the earth connection? Or do something else, so that I don't get turned into a delicious bacony Frazzle when I use the switch? ?

 

 

 

20201208_202437_resized.jpg

Those instructions are for a 240 volt installation, they don't consider you would use it on 12 volts

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4 minutes ago, BlueStringPudding said:

So I'm not going to get spooked by spark when I use it wired the same as the old one?

 

Not a big one , No.

 

240v stuff does not have a very long lifespan when switching 12v or 24v

Edited by matty40s
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4 minutes ago, Tacet said:

No need to earth a 12v switch.  Someone will be along soon to say that it is not ideally suited to switching the pump, but that is another matter.

Why is that not suited? I'm replacing like-for-like except for the cosmetic finish of the switch. Two pumps on my boat use what appear to be standard light switches for their on/off. They've not been queried by either any of the BSS assessors or the surveyor. In fact I vaguely recall that some years ago people on this forum explained to me exactly how to wire one in! 

 

(Shall I just leave them to argue amongst themselves on this, or do I need to go get some popcorn in case anything useful comes up?) ?

Just now, matty40s said:

Not a big one , No.

 

? I'm hoping not even a small one... ???

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4 minutes ago, Alan de Enfield said:

Because they cannot believe that anyone would try and use 230v AC switches on 12v DC.

 

It is not a good idea !

I for one would like to know why.

 

I've often done it in the past with no problem what so ever.

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23 minutes ago, Alan de Enfield said:

 

It tends to come up every few months.

See (amongst others) post#40

 

Lighting Top Trumps - Page 2 - Equipment - Canal World

A water pump in most installations doesn't 'switch' through its isolation switch.

 

It only would if the switch was operated whist the pump was running. So any arcing would be non existent.

Edited by The Happy Nomad
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5 minutes ago, The Happy Nomad said:

A water pump in most installations doesn't 'switch' through its isolation switch.

 

It only would if the switch was operated whist the pump was running. So any arcing would be non existent.

True that it would be very unlikely to need to be switched off while running - I think that's what you mean. But when switching on, if the pipes are empty then the pump would immediately start. Is that a risk when using either a 240v type switch, or one with a metal frontplate?

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13 minutes ago, BlueStringPudding said:

True that it would be very unlikely to need to be switched off while running - I think that's what you mean. But when switching on, if the pipes are empty then the pump would immediately start. Is that a risk when using either a 240v type switch, or one with a metal frontplate?

 

You have absolutely no chance of being 'electrically tickled' with 12v.

The problem is simply the wear and arcing on the contacts.

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My shower pump is switched  under electrical load, i.e. the full current flows on switching, likewise when I switch the pump off it is under load. This is done every day we are on board 3 times a day for the past 18 years so probably some 6000+ switches on and off and no sign of problems yet. When it does I will bin it and fit another that will see me out.

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My comment was on the switching, if something was switched on and off(and some people on boats do with water pumps because the sensor is faulty and it seems a good idea to save money)..the arcing will lead to a demise far sooner than a 12v switch unit.

If almost permanently on, then no, there shouldn't be a massive issue...

Or spark.

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I'm sure someone will be along soon to drone on about arcing and mains current cycling through zero and therefore mains switches aren't suitable for DC use etc. While this is true you have to decide is it dangerous or is it a nuisance. Its not dangerous the worst case is the switch contacts weld together. Is it a nuisance ? Guess only you can answer that...

 

A proper 12 volt DC rated switch would be better technically but you might not like the look or cost and it probably won't be direct fit either.

Edited by jonathanA
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30 minutes ago, BlueStringPudding said:

True that it would be very unlikely to need to be switched off while running - I think that's what you mean. But when switching on, if the pipes are empty then the pump would immediately start. Is that a risk when using either a 240v type switch, or one with a metal frontplate?

There is no risk. You do not need an earth.

 

You might get some arcing but the actual pump won't fire up untill it gets a supply. It can't do that untill it does. It may be a millisecond.but it will lag ever so behind.

 

I wouldn't worry.

 

 

 

  

Edited by The Happy Nomad
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11 minutes ago, matty40s said:

the arcing will lead to a demise far sooner than a 12v switch unit.

Yes, in theory the switch life is reduced at 12V dc compared with 240V ac. But as others have commented in practice they work fine, and the reduced life is unlikely to be as significant as suggested. After all, your previous switch managed just fine until you changed it for aesthetic reasons.

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I have has the odd 240v AC switch fail on 12v DC, some by welding together, some with broken contacts.  But most have been on sockets where a fair bit of current is broken.

 

This is over many years, some cheap accessories, after lots of use.  Don't worry about it.

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1 minute ago, David Mack said:

Yes, in theory the switch life is reduced at 12V dc compared with 240V ac. But as others have commented in practice they work fine, and the reduced life is unlikely to be as significant as suggested. After all, your previous switch managed just fine until you changed it for aesthetic reasons.

Thanks. Although I'm not changing it for aesthetic reasons. I'm changing it because I want thicker cables to the switch because there's some voltage drop through it, which has only become evident since installing a water pump that draws more oomph than its predecessor did. The old switch can't accommodate thicker cables and the ones currently fitted to it are very thin. It's not a huge amount of voltage drop and I don't know how much of it is attributable to the thin wires or the switch itself, but I might as well improve it while I've got things already dismantled in there.

The old switch (which still works) appears to have been installed by a previous owner, and I've had this boat nearly 14 years. So it's at least that old, possibly older, so it's lasted well. 

How I ended up with a metallic switch was simply down to the limitations of suppliers that offer click and collect from my local town, combined with a single pole switch so I don't have to try and cut a bigger recess in the wall, combined with a high enough amp rating plus a front plate that was about the same size as the one already in place - coz the wood around it has faded. So I've ended up with a cosmetic change because there was little to choose from!  But I don't mind that, the brushed steel effect will look fine in the kitchen. ?

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