Moving a pull light switch in the bathroom

[bernardgreen]

to my mind there has never been a need for RCD protection of 8 volt door bell wires.

There is no need provided the wires never come into contact with mains voltage. If the door bell is supplied from batteries then RCD protection is not needed. There is a case to consider protecting a door bell when it's ELV is supplied by a transformer from the mains. Insulation / isolation failure in the transformer could raise the ELV to 230 volts above ground making a wet door bell push potentially lethal to someone touching it.

I favour earthing one side of the ELV such that insulation / isolation failure in the transformer will result in current to earth from the mains via the ELV wiring and this earth current would trip an RCD

That said the isolation in a transformer with primary and secondary separated on split or dual bobbins is very unlikely to fail. Single bobbin transformers with primary and secondary windings separated only by a layer of tape insulation can fail.

 

[ericmark]

There is no need provided the wires never come into contact with mains voltage. If the door bell is supplied from batteries then RCD protection is not needed. There is a case to consider protecting a door bell when it's ELV is supplied by a transformer from the mains. Insulation / isolation failure in the transformer could raise the ELV to 230 volts above ground making a wet door bell push potentially lethal to someone touching it.

I favour earthing one side of the ELV such that insulation / isolation failure in the transformer will result in current to earth from the mains via the ELV wiring and this earth current would trip an RCD

That said the isolation in a transformer with primary and secondary separated on split or dual bobbins is very unlikely to fail. Single bobbin transformers with primary and secondary windings separated only by a layer of tape insulation can fail.

I can't see how you can fit a RCD to an 8 volt supply, most RCD's need voltage to work, they would never trip with 8 volt. Supply to the transformer is something else, it's the supply from the transformer I am talking about.

We have three ELV supplies SELV, FELV and PELV with SELV there should never be an earth connected to either leg, with PELV then one leg must be earthed, and with FELV it does not matter.

As to LV there is only one place in most houses where one leg is not earthed, that is the bathroom, as far as I am aware it is about the only place where we have an IT supply. I suppose you could fit a shaver outlet else where, but it's not normal.

 

[adm]

I did not intend to open up such a can of worms and my original post seems to be getting rather off topic.I have realised this ceiling is a suspended ceiling and having checked the wiring the earth from the wire fitted into the strip light has been cut back.but all I can see at the pull switch is the two red wires that attach into the mechanism itself as there is no give on the wires to pull any further through. Could it maybe that their is some connector block above the suspended ceiling that the wire from the light itself is connected to and then just two single strands of the red wire from this into the pull switch.

 

[bernardgreen]

I can't see how you can fit a RCD to an 8 volt supply,

Relatively easy. The source is centre tapped to ground and the two sides of the supply are each fed through low reistance counter wound coils on a common relay core. In normal operation the magnetic fields in the two coils cancel each other out.

with SELV there should never be an earth connected to either leg

The only reason for not earthing an ELV circuit is to prevent making a path for current to ground when someone is holding a bare ELV conductor in one hand and a mains voltage item in the other hand.

With SELV him indoors is safe until him outdoors touches the SELV wiring. ( OK it is a bit extreme but most accidents involve something at or beyond the extreme )

 

[securespark]

I did not intend to open up such a can of worms and my original post seems to be getting rather off topic.I have realised this ceiling is a suspended ceiling and having checked the wiring the earth from the wire fitted into the strip light has been cut back.but all I can see at the pull switch is the two red wires that attach into the mechanism itself as there is no give on the wires to pull any further through. Could it maybe that their is some connector block above the suspended ceiling that the wire from the light itself is connected to and then just two single strands of the red wire from this into the pull switch.

Easily.

As I said, the best thing to do would be to post some pix.

You need to ensure you have earth continuity. From what you have said, that is doubtful.

But pictures would go a long way to helping us help you!

 

[ericmark]

Forgetting our banter between each other, what you need to know is what is or is not missing and how much will it cost in time and money to bring it up to a point where it is considered safe. If a DIY guy works on an installation it is rare for any courts to find him guilty if some one is injured, they are much faster finding a tradesman to blame.

In the main an accident is not caused by one thing wrong, it is normally a whole list of things which have gone wrong, the Emma Shaw case is a good example, plumber, plaster, and electrical contractor all made errors, we in the trade tend to look at these cases and think there by the grace of god go I, as we all expect people to follow simple instructions, not rocket science to plug in a tester press the button and write down the reading, and if no reading simply write down no reading.

As a result we tend to be over careful, and follow the book to the letter, even then mistakes still happen. We can even argue about the regulations, if something is classed as SELV how every much you want to earth it regulations will not allow it.

So as said post pictures, and use some common sense, to my mind fitting a RCD makes an installation safer, and to say no I will not fit one unless you do this as well is morally wrong, even if following regulations, but to break rules because of a whim is very different.

So if asked to move a light switch down the wall so a wheel chair user can switch the light on, even if not to rules, I would likely still do it, but to move it to get an extra cupboard in likely I would say no. But put up pictures and see what people say.

 

[stillp]

Could it maybe that their is some connector block above the suspended ceiling that the wire from the light itself is connected to and then just two single strands of the red wire from this into the pull switch.

Could be, yes.

 

[securespark]

Please, sir, I said that, Sir.

 

[EFLImpudence]

It makes no mention of protecting property from fire

I would say that is what protecting persons from fire implies - unless you think persons will burst into flames when getting a shock.

nor does it mention protecting a person who is in the property but is not operating any switches or any other part of the installation.

Either - as above or are you considering remote shocks?

It seems to suggest that injury from touching a switch is acceptable but injury from operating the same switch is not acceptable.

I don't follow that one.

To me this is one reason why common sense and knowledge of hazards is more effective in protecting people and property than a book of bad written rules and guidelines.

Yes, agreed, but common sense is rare, isn't it? and it's not allowed nowadays, is it?

How about a book of well written rules and NO guide(line)s?

 

[ban-all-sheds]

unless you think persons will burst into flames when getting a shock.

http://www.nydailynews.com/archives/news/condemned-man-catches-fire-electric-chair-article-1.751043

 

[EFLImpudence]

I sit corrected.

 

[stillp]

Careful where you sit. Some chairs can kill.