light switch

vanillapod · Posted: Fri Jul 28, 2006 3:33 pm Post Subject: light switch

i replaced a one way switch with a metal type (which needs an earth) when i connected wires up as previous plastic switch I blew the fuse. Can anyone explain why? Thanks

Spark123 · Posted: Fri Jul 28, 2006 3:39 pm Post Subject:

Please can you tell us how you have connected the wires?

vanillapod · Posted: Fri Jul 28, 2006 4:22 pm Post Subject: light switch

will not be able to do so until monday but thanks for a quick reply

Dippy · Posted: Fri Jul 28, 2006 10:36 pm Post Subject:

Check for a short between the switch terminals and earth. The switch may have a manufacturing defect.

Taylortwocities · Posted: Fri Jul 28, 2006 10:42 pm Post Subject:

Almost impossible to wire it up so the fuse blows unless you have connected the cpc (earth wire) onto one of the switch terminals OR you have trapped one of the wires when u did up the screw.

I am assuming you have only one 2 core and earth cable coming into the switch box? The red (or brown) wire should go onto the COM terminal, the black (blue) wire goes on to the L1 terminal. The earth wire MUST go to the terminal on the plate of the switch itself and also to the earth terminal of the back box.

Note that the terminal layout of COM, L1 and L2 is different on some switches, dont assume that the terminal on its own is the COM. Some manufacturers like to confuse people - makes more work for us sparkys!

Tayla

breezer · Posted: Sat Jul 29, 2006 5:06 am Post Subject:

Dippy wrote:

Check for a short between the switch terminals and earth. The switch may have a manufacturing defect.

i dont think so, switches are generaly on or off, so if it is as you say faulty, it will be on or off all the time

i bet as its a metal box the wire is trapped / touching where it shoundn't

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Dippy · Posted: Mon Jul 31, 2006 12:33 pm Post Subject:

breezer wrote:

Dippy wrote:

Check for a short between the switch terminals and earth. The switch may have a manufacturing defect.

i dont think so, switches are generaly on or off, so if it is as you say faulty, it will be on or off all the time

i bet as its a metal box the wire is trapped / touching where it shoundn't

Not if the defect is part of the armature so that it only shorts in one position.

breezer · Posted: Mon Jul 31, 2006 2:29 pm Post Subject:

Dippy wrote:

Not if the defect is part of the armature so that it only shorts in one position.

I suggest you check how a switch works then

where is its "armature"
And what does a switch normaly do then if it does not connect (or short) one terminal to the other

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Taylortwocities · Posted: Mon Jul 31, 2006 6:27 pm Post Subject:

Its only a 'short' if a live conductor is connected to earth or neutral.

If the switch has only two conductors going into it then a short will only have the effect of turning the light on. If there is a fault with the switch to blow the fuse then it can only be a short between the switch mechanism and the (earthed) parts of the switch. OR a trapped wire.

Hopefully vanillapod will have been on site today and can illuminate us which is mare than his cusomers will have been for the last 4 days!

Tayla2

breezer · Posted: Mon Jul 31, 2006 6:37 pm Post Subject:

which is what i said, but dippy does not seem to be able to grasp the concept

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vanillapod · Posted: Tue Aug 01, 2006 7:17 am Post Subject:

As requested wiring is as follows:-
(looking at switch from the outside)
red to top of switch only one place this can go.
yellow to bottom right #blue to bottom left
green to earth on metal box.

New switch has ' one way' ' two way ' at bottom and says 'this switch must be earthed and there is a screw on the face plate for this....
Does this help or should I call an electrician?

Taylortwocities · Posted: Tue Aug 01, 2006 7:38 am Post Subject:

Sounds like iys a two way lighting circuit (there must be another switch that also turns the light on&off?).
Certainly the front plat must also be connected to earth but in any event the fuse should not blow. Light might not work or the light might be always on.

What happens when you replace the switch with the original (plastic) one? If its OK then the new switch may be the problem but keep your fingers off the metal switch plate especially if its not earthed, it may be live!

If old switch works OK get a new switch and/or get a sparky to help you/.

Tayla2

Dippy · Posted: Tue Aug 01, 2006 11:53 am Post Subject:

Breezer,

An armature is the moving part of an electromechanical device, which a light switch is.

Vanillapod clearly stated "i replaced a one way switch with a metal type (which needs an earth)" which means that most of the body of the light will be earthed, providing the possibility of the short to earth I mentioned.

Are you able to "grasp" this concept?

Tayla2 - neutral to earth is a short too.

Taylortwocities · Posted: Tue Aug 01, 2006 1:07 pm Post Subject:

Dippy, I've been sparking for many years and I know what a bleeding short is. You should know that a neutral to earth short will not blow the fuse (see his original post) It might trip an RCD if its in the circuit involved but not blow the fuse.

Also if you look at his recent post, the earth wire is connected to the back box, not the switch itself so when the switch is not screwed into the back box there's no path to earth. That's why I said dont touch it and get a sparky in. I'd sure like to know if the original switch works when its replaced. We are, of course assuming that no other works have been done that could cause the problem (a nail through one of the strappers to the other switch, maybe??)
Ahh Vanillapod. You say its a one way switch but you have got red, yellow & blue plus an earth, right? Something smells not right.

Tayla2