In what context do you use a CPC?

[Baker1988]

can anyone please link me to an image of a CPC please ...

this is a twin and cpc used mostly in domestic/houses the middle connductor without its own insulation is the cpc


This is swa (steel wire armored) cable used in places where you need protection to your cable like industrial/commercial/supply cables, you can buy this with a extra core and use that as the cpc but normally you use the steel armorings of the cable by useing the gland, here is a pic the outer steel is the cpc


Then there is mi (mineral insulated) cable also known as micc (mineral insulated copper clad) cable this is used where you need to maintain the circuit integrity during fire and stuff like on a fire alarm system as it can with stand a really high temp, it is the copper clad on the outside under the sheath that is used as the cpc


Hope this helps clarify a few things pal

 

[Floody]

Lmfao Trev, I never knew what the ral name for Zebs were either, also heard people calling them zebedees but no idea if that's the real name? Been using them for 9 months of 2012...

 

[KWCFC]

Why is the earth left bare in T+E out of interest? Why not insulated like the others and why smaller?

 

[trev]

1 To protect the cable if it's damaged along the run.
2 To save money

 

[Baker1988]

Why is the earth left bare in T+E out of interest? Why not insulated like the others and why smaller?

im not sure to be hones i think it is probily to save money in production as it is not designed to carry current all the time like the other too it is only there for fault current bus as i say not sure

 

[Baker1988]

1 To protect the cable if it's damaged along the run.
2 To save money

haha 1 is obvious but it did not even come into my head haha think its getting late haha

 

[not_today]

1 To protect the cable if it's damaged along the run.
2 To save money

Sorry trev im a bit confused, how does leaving the CPC or earth uninsulated protect it from damage? i can understand the need to save money and the fact it wont be carrying current very often if not at all.

 

[Baker1988]

Sorry trev im a bit confused, how does leaving the CPC or earth uninsulated protect it from damage? i can understand the need to save money and the fact it wont be carrying current very often if not at all.

well it doesnt protect it from actually being damaged but if it gets damaged like it gets cut or part of the insulation is removed as the cpc is connected to earth at one point in the circuit the live/neutral conductor will touch the cpc which wil create a fault path for the circuit and trip the mcb/rcd

 

[not_today]

i thin ive got it!

so it if the live or neutral are damaged inside the cable somehow, they will touch the bare wire and send the current to earth?

if it was covered then it would not go back to earth and could cause someone to have a nasty shock?

Sam

 

[trev]

well it doesnt protect it from actually being damaged but if it gets damaged like it gets cut or part of the insulation is removed as the cpc is connected to earth at one point in the circuit the live/neutral conductor will touch the cpc which wil create a fault path for the circuit and trip the mcb/rcd

Thanks for saving me some typing again mate

 

[Baker1988]

i thin ive got it!

so it if the live or neutral are damaged inside the cable somehow, they will touch the bare wire and send the current to earth?

if it was covered then it would not go back to earth and could cause someone to have a nasty shock?

Sam

yeah basically mate

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Thanks for saving me some typing again mate

lol sorry dont mean to jump in all the time

 

[trev]

lol sorry dont mean to jump in all the time

Don't be daft mate it's good that you answer each others questions if and when you can

 

[Paul.M]

Think I need to explain something for the trainees when it comes down to the exam matters. There are a few points to this important subject.

1. CPC (circuit protective conductor) has to be the full length of the current carrying conductors. As per the regs (therefore T&E, swa etc.)

2. An earth must be provided at each appliance point (sockets, light fitting, motors etc) and this is achieved via the CPC so providing an earth return path.

Both go down the same conductor but in the exams it will mean a different thing, eg:-

Q. You cut through a cable, what return path will the current flow? = CPC

Q. There is a fault from an appliance that trips the MCB, what return path does it take? = Earth via the CPC conductor.