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Ben Steele

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Hi to all,

I was wandering if i could possibly ask for a little help!

I've just started out in the job and have lots of questions which i would like answering:D

At work at the moment we have been installing ring mains and lighting circuitry but i'm a little foggy on how a 3 core cable works with a permanent and switch live.

It may seem like a really basic question to ask but i've literally just started out:confused:

Any answers would fab.
Thanks Ben
 
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A

acat

  • Thread Starter Thread Starter
  • #2
Hi Ben

Maybe its me but Im not sure what you are asking so I am making an assumption here that with the 3 core you are referring to lighting.

3 core is used for things like lights on the stairs the 3 core is used so that you can switch on the lights at the bottom of the stairs and turn them off at the top of the stairs. Its also used if you need an intermediate switch between downstairs 1st landing etc etc up the top of stairs.

If you are asking something totally different ignore me:)

Hope it helps

Chris
 
Hi Ben

3 core cable is only used for 2 way lighting. Do you mean T&E ie one brown (phase), one blue (neutral) and one yellow/green (earth).

If you mean T&E then basically you have a Live, a Neutral and an earth coming in from your CU to your ceiling rose. The live goes to a terminal called Permanent Live, Neutral to Neutral and Earth to Earth. You then have what is called a Switched Live, it's a cable from the Permanant Live down to the switch and back up to a terminal in the ceiling rose seperate to the permanent live called switched live. (Remember both wires in a switch are Live). Then Phase from the Switched Live terminal to the light bulb, Neutral from Neutral in ceiling rose to light bulb.

I have drawn a simple diagram, hope this helps.

Just ask if you're still not sure



Regards
Mark
 

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A

acat

  • Thread Starter Thread Starter
  • #4
Thanks Mark why didnt I think of a diagram:) Ben if it is for stairway lights I have a diagram that will explain it for you including intermediate switch send me a priate message with your email and I will scan it in and forward it to you

Chris
 
S

Spudnik

  • Thread Starter Thread Starter
  • #5
A 3 core and earth can also be used for a switch drop from a ceiling rose.

This would carry and perm live, the switched live and a neutral so that for eg, a single cable can be run from the 2 gang switch to an outside light.
 
A

acat

  • Thread Starter Thread Starter
  • #7
I agree thanks Jason didnt know that either if we said pretty pretty please could you do a diagram as to how it works when you get a chance.

Many thanks

Chris
 
S

Spudnik

  • Thread Starter Thread Starter
  • #8
Thanks Jason I didn't know that. How does it work?
Standard 3 plate ceiling rose, circuit in, circuit out.

instead of T&E drop to switch, use 3 c.

2 gang 2 way switch. use 2 cores for the rose as normal. loop the switch feed to other switch.

T&E from switch to outside light. L1 switch feed to light, last remaining core of 3c connect to neutral in rose and neutral for light in switch.

Hope that makes some sort of sense.

Ill do a diagram in a bit.

Watching Hells kitchen:D:D




Here we go.

Yes its a very bad drawing but gives you the rough idea.

 
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Des 56

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Arms
Esteemed
A light will work if it is supplied with a live to the light and a neutral returning from the light
That live to the light, could be taken to a switch first (permanent live), then to the light (this is the switched live)

An example of using a 3-core and earth for hall and external lights

A 3-core and earth from the hall light to 2-gang switch
a permanent live (brown)
a switched live (grey) with brown oversleeving
and neutral (black) with blue oversleeving to signify neutral Terminate in a connector block in the back box

The permanent live(Brown) can feed both sides of the switch
The switched live(Grey) can switch on the hallway light

If a twin and earth was run into this switch for an external light, then the unused switch, which has a permanent live, can now feed the brown of the external light through that switch
The blue of the external light can connect to the availble neutral in the connector block
 
S

spark1

  • Thread Starter Thread Starter
  • #10
Another common use for 3-core & cpc is in the supply to Timed extractor fans...here again you have Permanent line.....switched line ....neutral ..and cpc



spark1
 
B

Ben Steele

  • Thread Starter Thread Starter
  • #11
Hi to all,

Big thanks to everyone for the replys and diagrams, big help. Sounds like im not the only one who found this question usefull.

I have a much better understanding of 3 core now, this forum rock's :D

I must admit the drawing's looked quite intimidating at first but now it's starting to make sence. . . WooHoo.

Big thanks again to everyone for helping me.

I'll have the next question ready for you all soon lol

Thans Ben.
 
D

daver

  • Thread Starter Thread Starter
  • #12
A light will work if it is supplied with a live to the light and a neutral returning from the light
That live to the light, could be taken to a switch first (permanent live), then to the light (this is the switched live)

An example of using a 3-core and earth for hall and external lights

A 3-core and earth from the hall light to 2-gang switch
a permanent live (brown)
a switched live (grey) with brown oversleeving
and neutral (black) with blue oversleeving to signify neutral Terminate in a connector block in the back box

The permanent live(Brown) can feed both sides of the switch
The switched live(Grey) can switch on the hallway light

If a twin and earth was run into this switch for an external light, then the unused switch, which has a permanent live, can now feed the brown of the external light through that switch
The blue of the external light can connect to the availble neutral in the connector block
Hi Des

Is there a reg on identification of cores. I use the grey as neutral and sleeve blue and the black as switched live (sleeved brown). A lecturer quoted this and I have stuck with it. Cant find any reference.

Cheers
 
S

spark1

  • Thread Starter Thread Starter
  • #13
Daver you are correct in what you say......black & blue sleeved brown and grey sleeved blue....the intention is to get away from the presumption that black is neutral, cos in 3-phase it is now a line conductor.


spark1
 
D

daver

  • Thread Starter Thread Starter
  • #14
Daver you are correct in what you say......black & blue sleeved brown and grey sleeved blue....the intention is to get away from the presumption that black is neutral, cos in 3-phase it is now a line conductor.


spark1

Thanks Spark 1
 
Another common use for 3-core & cpc is in the supply to Timed extractor fans...here again you have Permanent line.....switched line ....neutral ..and cpc



spark1
also smoke alarms, L.N and link
and outside lights if you have a pir or solar switch ,permanent L.N and switchwire plus cpc of course
 
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