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Discuss Another..Replacing lost CPC? in the Electrical Forum area at ElectriciansForums.net

FatAlan

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Trainee Electrician
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Ok, so there have been a number of threads on old lighting circuits with no CPC. Also noted that it’s a no no to borrow a route to earth from another circuit.
In this scenario I have two lights atop of brick gate pillars. I have good continuity and sound IR between the two pillars along with a CPC. However there is an armoured feed from the house which comes up under one of the pillars. The end of the amour is not accessible due to concrete and block paving. I have live and neutral conductors but no earth. Would it be acceptable to run a new separate earth conductor back to the origin of the SWA also confirming that the SWA is correctly earthed at the origin?
 

DPG

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TA
Arms Access
Ok, so there have been a number of threads on old lighting circuits with no CPC. Also noted that it’s a no no to borrow a route to earth from another circuit.
In this scenario I have two lights atop of brick gate pillars. I have good continuity and sound IR between the two pillars along with a CPC. However there is an armoured feed from the house which comes up under one of the pillars. The end of the amour is not accessible due to concrete and block paving. I have live and neutral conductors but no earth. Would it be acceptable to run a new separate earth conductor back to the origin of the SWA also confirming that the SWA is correctly earthed at the origin?
Is the armour earthed at the supply end?
 

happyhippydad

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Arms Access
Subscribed Member
Ok, so there have been a number of threads on old lighting circuits with no CPC. Also noted that it’s a no no to borrow a route to earth from another circuit.
In this scenario I have two lights atop of brick gate pillars. I have good continuity and sound IR between the two pillars along with a CPC. However there is an armoured feed from the house which comes up under one of the pillars. The end of the amour is not accessible due to concrete and block paving. I have live and neutral conductors but no earth. Would it be acceptable to run a new separate earth conductor back to the origin of the SWA also confirming that the SWA is correctly earthed at the origin?
I'm not sure it is a no no to pinch an earth from another circuit.

See reg 543.1.2
 

happyhippydad

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Arms Access
Subscribed Member
I got the right answer before Westward! :D That will never happen again.
 

FatAlan

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Trainee Electrician
  • Thread Starter Thread Starter
  • #7
Just thought it would be bad practice to rely on a route back to earth via another circuit which without copious amounts of labelling, could be decommissioned leaving the other circuit unprotected.
 

westward10

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Staff member
TA
Arms Access
I must admit this could be an issue as a cpc covering more than one circuit probably harks back to the day where containment such as conduit was used as the shared cpc, frowned upon now but still perfectly acceptable. I think you need to take a view as to whether this is likely to happen but as it stands you would be doing nothing outside of the Regulations.
Post automatically merged:

Do you intend just to run a cpc back to the source of the cable, if so how would this involve a borrowed cpc.
 
Last edited:

FatAlan

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Trainee Electrician
  • Thread Starter Thread Starter
  • #9
I must admit this could be an issue as a cpc covering more than one circuit probably harks back to the day where containment such as conduit was used as the shared cpc, frowned upon now but still perfectly acceptable. I think you need to take a view as to whether this is likely to happen but as it stands you would be doing nothing outside of the Regulations.
Post automatically merged:

Do you intend just to run a cpc back to the source of the cable, if so how would this involve a borrowed cpc.
I can get an easier route back to another circuit (outside socket) if not an option I can find another route for a conductor back to the source but it would involve digging up a small section of concrete.
 

davesparks

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Arms Access
I would apply professional judgement to using the same cpc for multiple circuits. Is it obvious that the cpc is common to multiple circuits and how much risk is there of someone disconnecting it?

I regularly run multicore SWA to carry multiple circuits in stage lighting installations, the armour is the cpc for multiple circuits which is obvious to anyone looking and not easy to disconnect without disconnecting every circuit.

However a cpc taken from an outside socket to a gatepost to connect to the lights is not obvious and very easy to be disconnected.

How would the new cpc back to the origin of the SWA be installed? Would you be burying it?
Can you trace and expose the SWA at any point in its run? If so you could cut and joint it at that point and extend it to the gatepost to do the job properly.

The problem with running the seperate cpc is that you still leave a mystery SWA to T&E transition joint under the ground.
 

FatAlan

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Trainee Electrician
  • Thread Starter Thread Starter
  • #11
I would apply professional judgement to using the same cpc for multiple circuits. Is it obvious that the cpc is common to multiple circuits and how much risk is there of someone disconnecting it?

I regularly run multicore SWA to carry multiple circuits in stage lighting installations, the armour is the cpc for multiple circuits which is obvious to anyone looking and not easy to disconnect without disconnecting every circuit.

However a cpc taken from an outside socket to a gatepost to connect to the lights is not obvious and very easy to be disconnected.

How would the new cpc back to the origin of the SWA be installed? Would you be burying it?
Can you trace and expose the SWA at any point in its run? If so you could cut and joint it at that point and extend it to the gatepost to do the job properly.

The problem with running the seperate cpc is that you still leave a mystery SWA to T&E transition joint under the ground.
My chain of thought Dave. Ideally I’d like to find the SWA feed closer to the gate post, cut, joint and re feed back into the base but I suspect it enters under the block paving. May be some digging at the flowerbed at the house end wool give a better idea of the route.
 

westward10

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Staff member
TA
Arms Access
Modern wiring systems understandably consider a cpc unique to one circuit with the days of containment acting as an overall cpc long gone. I would and have ditched a redundant cable from a board without ever considering whether connected cpc was still serving a purpose so you are correct in considering whether this option is viable.
 

FatAlan

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Trainee Electrician
  • Thread Starter Thread Starter
  • #14
Just tt the gate posts. If you're lucky you'll clip the swa with the rod and earth the armour at the same time
Ah, you mean I could install an RCD at the base of the gate post and put a rod in? How about PME the neutral ;)
 

FatAlan

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Trainee Electrician
  • Thread Starter Thread Starter
  • #15
After wasting an hour or so digging for the SWA this morning I came up with the obvious solution. Just fuse down from the outside socket radial that I was going to borrow the earth from and try out one of them there Quinetic remote switches. I take it that the remote switch units will still operate from within a weather proof box?
 

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