Totally O/T External Domestic Wiring

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TopBanana
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Totally O/T External Domestic Wiring

Post by TopBanana » Sun Nov 25, 2018 5:28 pm

Apologies for the totally off topic question in advance.

Moved house in the summer, previous owner was a bit of a DIY enthusiast (polite way of saying I am finding lots of things that we weren't expecting), older house out in the middle of nowhere.

We have some external lighting which was working without issue until we tripped a fuse a month or so ago, hasn't worked since. The issue with the fuse was resolved immediately and I've got around to looking at the lighting today. The only thing I can see that I can't work out is in the attached pics.

Do I need to replace it, why is it wired like that ?

Appreciate some pointers for the electrical gurus on here.

Thanks
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tricky
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Re: Totally O/T External Domestic Wiring

Post by tricky » Sun Nov 25, 2018 5:50 pm

That emergency test part looks like it might have partially melted!

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Re: Totally O/T External Domestic Wiring

Post by jms2 » Sun Nov 25, 2018 5:51 pm

I'd not seen anything like that before, but googling it suggests that it is a keyswitch for interrupting the supply to a set of emergency lights, ie a system that switches on automatically and runs off batteries when the mains supply is lost.. The purpose of this is when you have an emergency lighting system, This switch is used (with a special key) to simulate failure of the mains voltage.

Why this has been used in a domestic context is not clear to me. What is also not clear is why this type of switch is ever needed - couldn't you just have a normal switch inside a locked cupboard?

I'm not sure whether the presence of this switch has anything to do with the lights not working. I would guess not.

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Re: Totally O/T External Domestic Wiring

Post by jms2 » Sun Nov 25, 2018 5:54 pm

tricky wrote:
Sun Nov 25, 2018 5:50 pm
That emergency test part looks like it might have partially melted!
I see what you mean. Might be worth replacing this with a normal switch and see what happens.

Maybe the power surge melted the keyswitch.
Last edited by jms2 on Sun Nov 25, 2018 5:55 pm, edited 1 time in total.

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Re: Totally O/T External Domestic Wiring

Post by tricky » Sun Nov 25, 2018 5:57 pm

I would check the wiring, as it might just be being used to terminate the wires.
Does it have mains across the red and black, that is, which pairs does it switch?

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Re: Totally O/T External Domestic Wiring

Post by 1024MAK » Sun Nov 25, 2018 6:15 pm

That type of switch is normally used to switch the supply to emergency “maintained” or “non-maintained” emergency fire escape lights and signs. They are also sometimes used in other industrial applications where a tamper resistant switch is required. For example to control lighting or equipment that should not normally be switched off.

In terms of wiring, the cable to it should use wires coloured to the “line” (called “live” by non-electricians) colour for both cores (the old U.K. standard was red, the current standard is brown) either by using the correct cable, or by using the correct coloured sleeving. Although you may also come across installations where insulation tape has been used (not recommended as it can fall off when the adhesive fails).

It is possible that the switch has been damaged (hence the melted looking front) if at some stage the cable to it had mains neutral connected to the black wire... thus causing a short circuit if/when the switch contacts are/were closed.

These switches are operated by a special key.

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Last edited by 1024MAK on Sun Nov 25, 2018 6:22 pm, edited 2 times in total.

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Re: Totally O/T External Domestic Wiring

Post by flaxcottage » Sun Nov 25, 2018 8:52 pm

I've seen this sort of wiring in lighting circuits before. Generally the red lead is a live input and the black lead is a live output to the rest of the lighting circuit. In the light fitting there will be the neutral wire also coloured black. The two blacks connect to the light bulb. In some of my light fittings there are up to three red wires and two black ones as well as earths.

That said, it does not mean that your example is the same. Electricians seem to have been a law unto themselves when connecting things in old houses.
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Re: Totally O/T External Domestic Wiring

Post by dp11 » Sun Nov 25, 2018 9:09 pm

flaxcottage wrote:
Sun Nov 25, 2018 8:52 pm
In some of my light fittings there are up to three red wires and two black ones as well as earths.
In a standard UK house lighting wiring ceiling rose there will be three reds , three backs, three earths ( if earthed) , plus the wires to the light. All the reds connect together ( But not any wires from the lamp). The twin & earth going to the light switch, the back wire should be sleeved red and go to the light bulb. The other end of the light bulb and the other two blacks connect together.

In new colours black wire are now blue and reds are now brown.
Last edited by dp11 on Mon Nov 26, 2018 12:47 am, edited 1 time in total.

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Re: Totally O/T External Domestic Wiring

Post by CMcDougall » Sun Nov 25, 2018 10:33 pm

http://www.google.com/aclk?sa=l&ai=DChc ... _wI&adurl=
those 'switches' are to test above light pic

do you have one, they have a green led on left when mains powered & then use 3.6v internal rechargeable battery when mains power is off.

Wiring is correct, but would change to a normal, those in yours are for 3 way hence L1/2/3/4 only need L1/2 , unless another switch like at bottom & top of stairs.
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Re: Totally O/T External Domestic Wiring

Post by jgharston » Mon Nov 26, 2018 12:02 am

Assuming it's correctly wired, what you've got there is loop-in lighting, where a single Twin+Earth supplies the live to the switch and also the switched live back from the switch to the light. As you are using two differently-coloured conductors to carry two lives, the "wrong" colour should be labelled to identify it.

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Re: Totally O/T External Domestic Wiring

Post by jgharston » Mon Nov 26, 2018 12:05 am

dp11 wrote:
Sun Nov 25, 2018 9:09 pm
ceiling rose ... All the reds connect together.
Argh!!!! NO NO NO!!! That results in the light being permanently on, and the switch becoming a "BLOW FUSE NOW!" activator. Ignore the colours, connect by function:
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Re: Totally O/T External Domestic Wiring

Post by dp11 » Mon Nov 26, 2018 12:45 am

jgharston wrote:
Mon Nov 26, 2018 12:05 am
dp11 wrote:
Sun Nov 25, 2018 9:09 pm
ceiling rose ... All the reds connect together.
Argh!!!! NO NO NO!!! That results in the light being permanently on, and the switch becoming a "BLOW FUSE NOW!" activator. Ignore the colours, connect by function:
I think if you read the whole paragraph you will find it is is correct. I don't define the colour of the lamp holder cable but describe how it is connected.
I've added a bit to make it even clearer.
Can you explain how it it can be miss understood and become a "BLOW FUSE NOW? NB I don't say connect all the blacks together
Last edited by dp11 on Mon Nov 26, 2018 1:21 am, edited 1 time in total.

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Re: Totally O/T External Domestic Wiring

Post by Kazzie » Mon Nov 26, 2018 6:34 am

jms2 wrote:
Sun Nov 25, 2018 5:51 pm
I'd not seen anything like that before, but googling it suggests that it is a keyswitch for interrupting the supply to a set of emergency lights, ie a system that switches on automatically and runs off batteries when the mains supply is lost.. The purpose of this is when you have an emergency lighting system, This switch is used (with a special key) to simulate failure of the mains voltage.
I've also encountered this type of switch used as a master switch for shop floor lights: a conventional switch in a publicly accessible place can be too much of a temptation for some pranksters.

You could locate the switch behind the desk, but H&S risk assessors would be concerned about expecting staff to walk from the front door to the desk in the dark on a daily basis. Hence, in new shop refits, there'll be one of these switches fitted near the door.
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Re: Totally O/T External Domestic Wiring

Post by jgharston » Tue Nov 27, 2018 1:03 am

dp11 wrote:
Mon Nov 26, 2018 12:45 am
jgharston wrote:
Mon Nov 26, 2018 12:05 am
dp11 wrote:
Sun Nov 25, 2018 9:09 pm
ceiling rose ... All the reds connect together.
Argh!!!! NO NO NO!!! That results in the light being permanently on, and the switch becoming a "BLOW FUSE NOW!" activator. Ignore the colours, connect by function:
I think if you read the whole paragraph you will find it is is correct. I don't define the colour of the lamp holder cable but describe how it is connected.
I've added a bit to make it even clearer.
Can you explain how it it can be miss understood and become a "BLOW FUSE NOW? NB I don't say connect all the blacks together
"connect all the reds..." is a trigger, I have to jump in. All too often the process of "connect all the reds together" finishes with "connect all the blacks together" which results in the lamp permantly connected across Live and Neutral, and the switch also connected across Live and Neutral. All too easy for novices to do when confronted with three cables sticking out of the ceiling. There were two chaps on my C&G course who just couldn't get it into their head that you wired up by function not by colour, and I had a tenant who optimistically replaced a ceiling rose and wired it up that way, and couldn't understand what or why he'd got it wrong.

It's the main reason why, when installing lighting from scratch, I use junction boxes to ensure all outlets/accessories have solely a single cable feeding them.

I once discovered that the standard lamp a tenant reported as not working was because it had been wired such that the lamp was across Earth and Neutral and the ground was connected to Live. Argh!!!

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