Adding to existing lighting with no CPC

[TomSparkman]

Hi everyone,

I am currently installing an additional 4 way CU which is to serve a new extension on the customers house. They have also asked me to alter one of their existing 2 way stairs lighting so that they can have an intermediate switch incorporated (a switch at either end of the upstairs landing aswell as the one at the bottom of the stairs).
Pretty straightforward... pull a 3 for from tbe existing switch to the extra one and the swap the existing to an intermediate.
The problem is that there is no cpc present at the existing switch. It is wired early 1970's style using a single brown with sheath (no earth) as the switch live back to the rose.

In order to do the work they have asked for do i need to completely rewire/wire in a cpc for that lighting circuit?
Or would it be acceptable to take a single earth from one of the new circuits i have installed, to the new switch i am adding to tbe existing circuit?

Its probably a simple answer but would appreciate constructive responses, thanks

 

[Pete999]

Hi everyone,

I am currently installing an additional 4 way CU which is to serve a new extension on the customers house. They have also asked me to alter one of their existing 2 way stairs lighting so that they can have an intermediate switch incorporated (a switch at either end of the upstairs landing aswell as the one at the bottom of the stairs).
Pretty straightforward... pull a 3 for from tbe existing switch to the extra one and the swap the existing to an intermediate.
The problem is that there is no cpc present at the existing switch. It is wired early 1970's style using a single brown with sheath (no earth) as the switch live back to the rose.

In order to do the work they have asked for do i need to completely rewire/wire in a cpc for that lighting circuit?
Or would it be acceptable to take a single earth from one of the new circuits i have installed, to the new switch i am adding to tbe existing circuit?

Its probably a simple answer but would appreciate constructive responses, thanks

Have you explained / told your customer that the circuit they want altered has no cpc? therefore no metallic fittings can be used.
In order to provide a cpc to all the points on this particular circuit, assuming it's not wired in cnduit, you will need to pull in a 4mm2 cpc from the CU in order to provide the circuit in question with a suitable cpc

 

[LankyWill]

Why a 4mm? 1.5mm should suffice for a lighting circuit. If they don't want a rewire your only other option is to pull in a cpc or use plastic accessories. I'd advise them to have a rewire due to the age of the installation and to bring them up to standard.

 

[Pete999]

Why a 4mm? 1.5mm should suffice for a lighting circuit. If they don't want a rewire your only other option is to pull in a cpc or use plastic accessories. I'd advise them to have a rewire due to the age of the installation and to bring them up to standard.

I you are pulling a cpc / earth wire without mechanical protection then 4mm is the size specified by 7671 or it was, you need to check you copy of 7671 for confirmation of my statement

 

[LankyWill]

@Pete999

I think that refers to bonding cable sizes in regards to TT systems. The conduit would provide the mechanic protection in the op's case.

 

[Pete999]

@Pete999

I think that refers to bonding cable sizes in regards to TT systems. The conduit would provide the mechanic protection in the op's case.

Does the op mention that the installation is wired in conduit? Regulation 543.1.1 page 164 in the BYB

 

[westward10]

Minimum size for an unenclosed cpc or bond is 4.0.

 

[westward10]

Is it only the switch cables which do not incorporate cpcs. Single browns in the 1970s?

 

[LankyWill]

@Pete999

I must have mistook your comment in your post about conduit as the actual scenario.

I am in the wrong, please don't send @telectrix round to teach me the errors of my ways.

Sorry almighty Jedi

Padwan

 

[Pete999]

Minimum size for an unenclosed cpc or bond is 4.0.

That's what I said, didn't I?

 

[Pete999]

@Pete999

I must have mistook your comment in your post about conduit as the actual scenario.

I am in the wrong, please don't send @telectrix round to teach me the errors of my ways.

Sorry almighty Jedi

Padwan

That's OK young Jedi I will not inform Lord Vadar, although he has probably read it all by now, may the force be with you, you should take your light saber with you and disappear to the Death Star for a few weeks

 

[telectrix]

@Pete999

I must have mistook your comment in your post about conduit as the actual scenario.

I am in the wrong, please don't send @telectrix round to teach me the errors of my ways.

Sorry almighty Jedi

Padwan

a bit far for me to bring my cane. i have to delegate your punishment to pete999.

 

[Pete999]

a bit far for me to bring my cane. i have to delegate your punishment to pete999.

None of us are perfect My Lord no punishment required

 

[TomSparkman]

Have you explained / told your customer that the circuit they want altered has no cpc? therefore no metallic fittings can be used.
In order to provide a cpc to all the points on this particular circuit, assuming it's not wired in cnduit, you will need to pull in a 4mm2 cpc from the CU in order to provide the circuit in question with a suitable cpc

No i havent told the customer yet, they were out by the time i had left.

Just to clarify:
This is a domestic property, so no conduit.

There is a cpc at the ceiling rose, just no sign at the switches. This may be due to being cut off outside of the backboxes in the wall or that there isnt a cpc in the cables at all.

The additional new switch and all of the existing accessories are non metallic.

I was thinking as long as the new strapper that i pull in is earthed then that should suffice. But from what you guys are saying it sounds like i have to bring the whole circuit up to date with a cpc?
As said above could i take a single earth (either 4mm or 1.5mm insulated and sheathed earth if its available) from one of the new lighting circuits to just earth the new strapper?

 

[westward10]

What are you going to use for the new strapper a three core and cpc.