Two core wiring with the same sleeve colour

[legend99]

Just asking more for my own curiosity if that's okay. When running say cable when both wires are the same colour sleeve, say dual blue or brown, and there is no power in the circuit yet, how do electricians know which wire is which at each end?!
Thanks and apologies for the possibly annoying question but I'm just curious to know

 

[SparkyChick]

For twin and earth, we meticulously make sure we keep track of the which side a particular core is on....

Just kidding of course

Since most of the cables we use have two cores plus an earth (or some other core), providing you can definitely identify one of the cores, using a continuity tester you can identify the others.

Join core 1 to the one you know and then go to the other end of the cable run and look for continuity between the one you know and the others... where you get continuity should be core 1. Rinse and repeat for other cores. If you don't have a known core you can use a long lead continuity test which uses a very long test lead connected to one end of the cable and then a normal lead at the other end to look for continuity on the cores.... this would typically be done with a low resistance ohm meter like the one built into most MFTs.

Hope this helps

 

[westward10]

Continuity tests.

 

[legend99]

For twin and earth, we meticulously make sure we keep track of the which side a particular core is on....

Just kidding of course

Since most of the cables we use have two cores plus an earth (or some other core), providing you can definitely identify one of the cores, using a continuity tester you can identify the others.

Join core 1 to the one you know and then go to the other end of the cable run and look for continuity between the one you know and the others... where you get continuity should be core 1. Rinse and repeat for other cores. If you don't have a known core you can use a long lead continuity test which uses a very long test lead connected to one end of the cable and then a normal lead at the other end to look for continuity on the cores.... this would typically be done with a low resistance ohm meter like the one built into most MFTs.

Hope this helps

Thanks a million! And so logical actually! Earth and one core joined at one end - and the continuity at the other end with earth and trying both cores. Obvious when you explain it. You sparkies are a lot brighter than you look!!

 

[James]

Thanks a million! And so logical actually! Earth and one core joined at one end - and the continuity at the other end with earth and trying both cores. Obvious when you explain it. You sparkies are a lot brighter than you look!!

Spare a thought for those of us that look brighter than we are in real life!!

a similar test is done when you have for example a 3 wire switch
com
n/o
n/c

3 wires brown black and yellow (for example.)
find the 2 that have continuity
i.e black and yellow

then hold the switch down and retest the combinations of brown to yellow and brown to black
if you get continuity then brown must be the n/o contact
the wire that you get continuity to brown when switch is closed must be the com terminal i.e. black
therefore the yellow must be n/c

 

[nicebutdim]

Up in this colder part of the island twin brown is generally only used for switch wires or strappers. Sometimes you have slightly different shades of brown which can be used to keep track of cores, but the worst that will happen is a switch in the wrong position needing cores swapped around.

I've never seen twin blue and any other cable I use with same coloured cores would be control cables in which all cores are black, but numbered.

 

[legend99]

Spare a thought for those of us that look brighter than we are in real life!!

a similar test is done when you have for example a 3 wire switch
com
n/o
n/c

3 wires brown black and yellow (for example.)
find the 2 that have continuity
i.e black and yellow

then hold the switch down and retest the combinations of brown to yellow and brown to black
if you get continuity then brown must be the n/o contact
the wire that you get continuity to brown when switch is closed must be the com terminal i.e. black
therefore the yellow must be n/c

The engineer in me was obliged to look it up. Can't quite picture it so I'll end up having to bloody figure it out now!

All joking aside, I really like the logic and the engineering side of wiring so appreciate you taking the time to describe it.

 

[legend99]

Up in this colder part of the island twin brown is generally only used for switch wires or strappers. Sometimes you have slightly different shades of brown which can be used to keep track of cores, but the worst that will happen is a switch in the wrong position needing cores swapped around.

I've never seen twin blue and any other cable I use with same coloured cores would be control cables in which all cores are black, but numbered.

Funnily enough, I replaced 4 core cable between immersion switch and immersion. Here in ROI, we usually have twin immersion elements - usually a bigger element for the bath and a smaller one for the sink - so you need 4 core. The wire was probably 20 years old and it seemed a little brittle so I got new 2.5 heat resistant 4 core. When I opened the box, the old wire had 2 browns and I was like how can you tell which is which? When I looked more closely, I realised the two browns were actually numbered - a little number 1 and 2 every few cms. The two elements can be identified as they have different resistance values so measured that on my multimeter and wired it back kn with the new 4 core which was blue, brown and black - with the brown and black being used to carry live to either the bath or sink element as our on switches for immersions also have a switch where you pick which element you want on (only one at a time obviously as the bath element is usually 3kw and the sink 2kw so would overload if both could come on together in most scenarios as wiring not rated for it).

Funny too you should say about colours on twin core - we had a job done here a year or so ago and the electrician left behind cuts of cable etc and one of the cables was a two core with earth where both cores were blue and I was wondering what it might be used for....

 

[oscar21]

Cant say I've ever seen a twin blue cable so I did a quick google and the nearest it came up with is a twin brown cable in a blue sheath, I've seen grey and white sheath and of course the old black rubber but never blue, does it have a specific use, I know the red 3core&E is used on fire/smoke alarm circuits occasionally.

Doncaster Cables 6242Y 1.5mm 100M 2 Core Blue Twin & Earth Cable (Per Reel)

Doncaster Cables 6242Y 1.5mm 100M 2 Core Blue Twin & Earth Cable (Per Reel)Key FeaturesColour: BlueMaterial: PVC insulated/sheathedConductor size: 1.5mmLength: 100 MetresBASEC approved300 - 500VBS6004Product code: 6241Y1.5BL-100MManufacturer: Doncaster Cables

www.expertelectrical.co.uk

 

[legend99]

Cant say I've ever seen a twin blue cable so I did a quick google and the nearest it came up with is a twin brown cable in a blue sheath, I've seen grey and white sheath and of course the old black rubber but never blue, does it have a specific use, I know the red 3core&E is used on fire/smoke alarm circuits occasionally.

Doncaster Cables 6242Y 1.5mm 100M 2 Core Blue Twin & Earth Cable (Per Reel)

Doncaster Cables 6242Y 1.5mm 100M 2 Core Blue Twin & Earth Cable (Per Reel)Key FeaturesColour: BlueMaterial: PVC insulated/sheathedConductor size: 1.5mmLength: 100 MetresBASEC approved300 - 500VBS6004Product code: 6241Y1.5BL-100MManufacturer: Doncaster Cables

www.expertelectrical.co.uk

You know what? I must have been mixed up and I'd guess it was brown/brown and earth. It was just a few off cuts and an empty roll for one of the cables and I would be happy to admit I think I have it wrong. Given it was domestic, I'd guess it was 2.5 t&e, 1.5 t&e, single brown, single blue, single earth and brown/brown with earth. That makes more sense - so I'll show my lack of brightness and withdraw my previous posting. Apologies!

 

[ipf]

That makes more sense - so I'll show my lack of brightness and withdraw my previous posting. Apologies!

Suggest staying switched on.

 

[Risteard]

I've never come across twin blue and would doubt that it exists as there is no obvious reason for it to exist.

 

[nicebutdim]

You know what? I must have been mixed up and I'd guess it was brown/brown and earth. It was just a few off cuts and an empty roll for one of the cables and I would be happy to admit I think I have it wrong. Given it was domestic, I'd guess it was 2.5 t&e, 1.5 t&e, single brown, single blue, single earth and brown/brown with earth. That makes more sense - so I'll show my lack of brightness and withdraw my previous posting. Apologies!

No idea why twin brown is still commonly used up here, when it's pretty much unheard of in GB. Certainly a better option than unsleeved blue conductors.

 

[ipf]

No idea why twin brown is still commonly used up here, when it's pretty much unheard of in GB. Certainly a better option than unsleeved blue conductors.

It’s available if required but it’s probably more a case of why carry another drum of cable just for the sake of switch wiring. I must admit I’ve hardly ever used it.
Red/brown that is, not black/blue.

 

[nicebutdim]

I like being able to identify strappers without having to read painted or plaster coated sheaths, but it's not something I generally use. Conversely every spark I know uses the stuff, but that's probably a good thing as none of them ever carry any sleeving that isn't green/yellow.

 

[Risteard]

I like being able to identify strappers without having to read painted or plaster coated sheaths, but it's not something I generally use. Conversely every spark I know uses the stuff, but that's probably a good thing as none of them ever carry any sleeving that isn't green/yellow.

Brown & blue for switch drops is unheard of here (and incidentally expressly prohibited across the border).

 

[nicebutdim]

Brown & blue for switch drops is unheard of here (and incidentally expressly prohibited across the border).

I wouldn't say it's unheard of, but certainly uncommon. There's no regulatory reason for not using blue/brown T&E on switch drops, provided conductors are correctly identified.

I didn't realise that ROI mandates the use of twin brown for switch drops - in light of that it's surprising the OP had never seen it before.

 

[ipf]

For the OP.
It is the norm for two (or all) blacks with one type of cable, and hence the 'belling out'/continuity as well as IR testing....pyro.

 

[Marvo]

Apart from ripcord and maybe a speciality flat elevator type ribbon cable I've also never seen a cable with two identical blue wires. I highly doubt such a cable would be available unless it was a special order. I've seen cables that contain more than 1 black wires with numbers on them but the numbers only appear every 10 or 15cm along their length so you might not see them if you only strip a short section.