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evo666

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i have been working with my little Nephew and he ask me this question.......


Why are there 3 wires (T+E) and the middle one is not coated in anything?

Bloody good question that I could not answer :confused:
Anyone know why the CPC wire in T+E is not insulated?
 
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Unregistered

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  • #2
to make the stripping alot easier??
 
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markthespark

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  • #3
Erm i think its to do with the ease of stripping and also the cable would be thicker if the cpc was insualted. Also more insualtion more cost.
 
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Cirrus

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  • #4
It does make sense though if the cpc was insulated - save sooo much time pratting about cutting sleeving to size all the time
 
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evo666

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  • #5
You see it takes a childs mind to ask the most simple questions :)

(and I just had to edit all the spelling mistakes!!)
 
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TonyM58

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  • #6
Its not insulated for the same reason as you earth the armour of SWA or the screen of screened cable.

consider if you put a nail through tw&E. If it goes through either of the live conductors, and will almost certainly ALSO touch the bare CPC completing the fault circuit for the CPD to operate (depending on how it is protected.)

we used to use a lot of screened cable for temporary circuits outdoors. I always use to explain this to my lads by saying that if you was to put a shovel through the cable, and you had an insualted cpc and live, you would have to hit them both with the shovel at the same time. With an earthed screen/armour, the shovel will almost certainly be in contact with it when it hits the live, completing the fault circuit.

of course, its cheaper as well for tw&e, but my explanation has always worked for me!!:rolleyes:
 
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Cirrus

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  • #7
Fook -knew you would hold the answer Tony:D
 
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DadofTwo

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  • #8
It is indeed a mighty fine question but you see it's only ever kids who ask the good ones.

The CPC ain't insulated because...

...in the event of insulation breakdown (or in the majority of cases, damage by accident or negligence) on the other conductors, the fault will be earthed (and will therefore trip the RCD or MCB or blow a fuse whereas if the CPC was insulated it would require the breakdown of the CPC insulation too in orer to earth the fault and as such, the fault could go un-noticed.
 
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DanBrown

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  • #9
Hiya Guys,

I was always led to believe that the reason for the CPC (earth) not to be covered with insulation is the fact that it gives better protection. When i say better protection, what i mean is - if you accidentally nail through the cable you have a much better chance of clipping the earth also as it is un-insulated. That is also why the earth is in the middle of the cable, to give a better chance of making contact with the earth in case of a nail fault or similar
Hope that helps, and was always led to believe this from college.
 
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DadofTwo

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  • #11
Hiya Guys,

I was always led to believe that the reason for the CPC (earth) not to be covered with insulation is the fact that it gives better protection. When i say better protection, what i mean is - if you accidentally nail through the cable you have a much better chance of clipping the earth also as it is un-insulated. That is also why the earth is in the middle of the cable, to give a better chance of making contact with the earth in case of a nail fault or similar
Hope that helps, and was always led to believe this from college.
Hmmm, wasn't that what I said 36 hours previous?
 
M

Mutts

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  • #12
Just been on holiday to New Zealand, and I was having a look over a friends electrics. (I know I couldn't help myself). I was suprised to find that the t&e over there does have an insulated earth. Maybe we are just behind the times!!!!!
 
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Spudmiester

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  • #13
There is some T&E with sleaved cpc. Used for exhibition contracting to save time !
 
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supasparx

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  • #14
There is some T&E with sleaved cpc. Used for exhibition contracting to save time !

Yeah I've come across this myself.

I tend to agree with the suggestion that the earth conductor is uninsulated to give better fault indication. But if that is the case, why is the earth in flex insulated?

I know flex is alot less likely to come in contact with a nail or screw but it is prone to being pinched, trapped or general sheath damage.
 
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DadofTwo

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  • #15
Yeah I've come across this myself.

I tend to agree with the suggestion that the earth conductor is uninsulated to give better fault indication. But if that is the case, why is the earth in flex insulated?

I know flex is alot less likely to come in contact with a nail or screw but it is prone to being pinched, trapped or general sheath damage.
At a guess, because flex is stranded and the only real way to control the strands is to enclose them in insulation.

Regards
 
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rumrunner

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  • #16
Good answer dadoftwo,i think your right,better wait untill shakey agrees,before getting too excited but i think your rite :D,
atvbitwww
 
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supasparx

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  • #17
At a guess, because flex is stranded and the only real way to control the strands is to enclose them in insulation.

Regards
Yes, you've just taught me to engage brain before keyboard.:eek:
 
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rumrunner

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  • #18
Not at all ,if everyone engaged there brain before key board then no one except maybee shake would post anything.
its the questions ,such as yours ,which although the answers are not immediately apparent ,but teach us the intricaces of our complex trade
and remember every one.f you dont know ASK i
ATVBITWWW
 
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Shakey

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  • #19
Yeah I've come across this myself.

I tend to agree with the suggestion that the earth conductor is uninsulated to give better fault indication. But if that is the case, why is the earth in flex insulated?

I know flex is alot less likely to come in contact with a nail or screw but it is prone to being pinched, trapped or general sheath damage.
Because: Flat twin & earth is exactly that - flat, and should be laid as such. so if a nail goes through it it is almost certain to hit a live conductor and the bare cpc.

with flex, it can be laying anyway on a surface, and a lot of flex is actually toroidal in structure (it curves in a helix like fashion throughout its length) so you could never be sure as to what conductors you will hit.

plus flex is far more prone to damage because its used for equipment supplies etc, and needs the additional protection. Tw&E of course, is 'static' when installed.

job done;);)
 

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