CPC/Earth feed to Light Switch Back Box

[BettyBoop44]

Hi
Just a bit of info required , just been checking all over the house checking for a earth feed to light fittings and switches , ( a friend informed yesterday that there friend have more or less sold there house , but an electrcal inspection has come up with no cpc to all the light switches ) .
I have found 3 light switch back boxes that do not have a earth feed to them , now the question is can I fit a plastic box inplace of the metal one that is in there and not need a earth feed to them ! .
All the light fittings have a earth feed to them ! , every circuit in the house is protected by a RCD .
cheers
BB

 

[Pete999]

Hi
Just a bit of info required , just been checking all over the house checking for a earth feed to light fittings and switches , ( a friend informed yesterday that there friend have more or less sold there house , but an electrcal inspection has come up with no cpc to all the light switches ) .
I have found 3 light switch back boxes that do not have a earth feed to them , now the question is can I fit a plastic box inplace of the metal one that is in there and not need a earth feed to them ! .
All the light fittings have a earth feed to them ! , every circuit in the house is protected by a RCD .
cheers
BB

Has the cable at the switch had cpc cut off where the cable enters the box?

 

[BettyBoop44]

Hi
Thanks for your reply , no there is no earth wire to the box ,only twin core cable .

cheers

BB

 

[Pete999]

Hi
Thanks for your reply , no there is no earth wire to the box ,only twin core cable .

cheers

BB

Not been snipped off where the outer sheathing finishes?

 

[BettyBoop44]

No just 2 core flat

 

[Pete999]

No just 2 core flat

So twin and earth from light to light with a twin to the switched, odd. Did the inspection produce any testing results? as it stands your friend can only use plstic switched, so no changing to fancy metallic switches.

 

[davesparks]

I've seen this as lot as it was quite common around here for the feeds to be wired in 3/029 twin&earth with the switch drops in twin 1/044.

The solution to this is to replace the switch drop cables with T&E after testing the circuit to confirm that the CPC present is viable and compliant.
But you should also consider that this is an old installation and there may be other things which require improvement. Adding a CPC to a few plastic switches is a bit pointless if the main earthing and bonding aren't up to scratch!

 

[davesparks]

So twin and earth from light to light with a twin to the switched, odd. .

Pretty common around here, I've fixed a few installations like this when I was doing domestics. Usually they have conduit down to the switches so it's an easy job to replace the switch drop with twin.
I think the reason it was done like this is that it was done when rewireing and the 3/029 twin didn't fit down the narrow conduits already in the wall.

 

[westward10]

Any chance of a pic for one of the back boxes.

 

[BettyBoop44]

So twin and earth from light to light with a twin to the switched, odd. Did the inspection produce any testing results? as it stands your friend can only use plstic switched, so no changing to fancy metallic switches.

Hi
Thanks for your reply , I am talking about my house not my friends friends house ! , the feed to the lights were also just 2 core flat , I fit a cpc to them a long time ago direct from the cpc bonding terminal next to the meter ,but did not think about the light switches , the kitchen and lounge light switches have a cpc they where put in when some workwas done there prob about 5 year ago .

cheers

BB

 

[BettyBoop44]

Hi
I really need a answer to my first post ie , can I fit a plastic back box in place of the metal one and then not need a cpc !

 

[LankyWill]

yes you could fit a plastic box in leui of a metal one, but remember the accessory would also have to be plastic. Are they cpc's at the light fittings?

 

[BettyBoop44]

Hi
Thanks for your reply , can you please read my #10 post .

cheers

 

[Pat H]

If the back box and light switch are both non metallic then no CPC is required.
However care must be taken that a later owner doesn't add metal faced switches and a risk is created. We don't rely on RCD for protection as they can fail.
You could leave a note in the plastic backbox as a reminder that no CPC is present and no metal switches to be installed as a sort of gift to the next owner.

 

[westward10]

Hi
I really need a answer to my first post ie , can I fit a plastic back box in place of the metal one and then not need a cpc !

I assume these are flush to the wall boxes and plastic isn't ideal for this. Do the existing boxes have plastic lugs for the cover screws.

 

[Pat H]

I assume these are flush to the wall boxes and plastic isn't ideal for this. Do the existing boxes have plastic lugs for the cover screws.

Good point. One of the common issues with light switches is the screws from the face plate being long and puncturing the wires behind. Potentially leaving a live screw head.
A plastic push in cover for each screw helps reduce that risk. Also taking care of the position of the cables as the face plate closes up and the length of the securing screws helps.

 

[Pete999]

If the back box and light switch are both non metallic then no CPC is required.
However care must be taken that a later owner doesn't add metal faced switches and a risk is created. We don't rely on RCD for protection as they can fail.
You could leave a note in the plastic backbox as a reminder that no CPC is present and no metal switches to be installed as a sort of gift to the next owner.

Earthing may not be needed, but cpcs need to be present regardless

 

[Pete999]

Hi
Thanks for your reply , I am talking about my house not my friends friends house ! , the feed to the lights were also just 2 core flat , I fit a cpc to them a long time ago direct from the cpc bonding terminal next to the meter ,but did not think about the light switches , the kitchen and lounge light switches have a cpc they where put in when some workwas done there prob about 5 year ago .

cheers

BB

BB your post has become confusing, what you need is a comprehensive EICR Electrical Installation Condition Report carried out by a competent Electrician, things have become difficult being drip fed information, get a Spark in to do the EICR and go from there.

 

[Des 56]

What size cpc and what routing did you take when installing he seperate cpc as there are regulations governing what should be done

 

[Ian1981]

1. Taken from best practice guide 1 with installation containing no cpc to lights.
   This is regarding a consumer unit change but nevertheless contains some useful information I think.
   Sorry about the quality as it's copied and pasted
   
   Carry out a continuity test applied between the earthing terminal in the exis ng consumer unit and all Class I light fittings and metal plate accessories.
   
   If the resistance value is 1 Ω or less, the equipment may be considered to be earthed.
   

1. 10.5.3. An insula on resistance test should be applied between the live conductors (line and neutral connected together) and the earthing terminal in the consumer unit, with that terminal connected to the means of earthing.
   
   The resistance should be at least 1 MΩ.
   
   
2. 10.5.4. An insula on resistance test should be applied between line and neutral connected together
   and the exposed-conduc ve-parts of every Class I lighting and metal switch plate found to not be earthed by the con nuity tes ng described in Sec on 10.5.2.
   
   The resistance should be at least 1 MΩ.
   

10.5.5 If the circuit does not ful l the requirements
of either 10.5.3 or 10.5.4. there would be a
risk of electric shock if the circuit were to be re-energised. The customer must be advised in wri ng that this danger exists, and that the circuit must be disconnected from the supply and should not be connected into a new consumer unit.

10.6. If the customer will not agree to the risk assessment as described in Sec on 10.5. being carried out,
they should be advised that a ligh ng circuit having no protec ve conductor that has metal or Class I switches, light ngs or other accessories ed

is poten ally dangerous (and so would warrant a Code C2 classi ca on in an Electrical Installa on Condi on Report).

This will mean that the circuit cannot be connected into a new consumer unit (see Sec on 4.3 of this Guide).

10.7. It should be noted that the protec ve measure double or reinforced insula on is only applicable
to electrical installa ons or circuits therein that are under e ec ve supervision in normal use to ensure that no change is made that would impair the e ec veness of the protec ve measure (regula on 412.1.3). Domes c and similar premises falling within the scope of this Guide cannot be considered to be under e ec ve supervision.

 

[westward10]

Not saying a word it is Sunday.

 

[BettyBoop44]

OK guys thank you for all your feedback the conclusion they have to have a cpc to each box/switch , there is only 3 walls to chase down other half will not be happy though it has to be done , would not of looked if it was not for the info my friend told me .

thanks again

BB

 

[BettyBoop44]

What size cpc and what routing did you take when installing he seperate cpc as there are regulations governing what should be done

Hi
I took a 2.5mm direct from the earth bonding box next to meter ! , I have to also mention that this problem is only on the lower floor switches upstairs are all fine .
ps: what reg is it that covers that ! .
BB

I assume these are flush to the wall boxes and plastic isn't ideal for this. Do the existing boxes have plastic lugs for the cover screws.

Yes.

 

[Pete999]

OK guys thank you for all your feedback the conclusion they have to have a cpc to each box/switch , there is only 3 walls to chase down other half will not be happy though it has to be done , would not of looked if it was not for the info my friend told me .

thanks again

BB

And each light point

 

[Des 56]

Hi
I took a 2.5mm direct from the earth bonding box next to meter ! , I have to also mention that this problem is only on the lower floor switches upstairs are all fine .
ps: what reg is it that covers that ! .
BB


543.1.1

 

[BettyBoop44]

And each light point

Read my #10 post in this thread ! .

 

[davesparks]

Hi
I really need a answer to my first post ie , can I fit a plastic back box in place of the metal one and then not need a cpc !

No, the regulations require that the cpc be present at every point in the circuit regardless of materials used.

 

[davesparks]

If the back box and light switch are both non metallic then no CPC is required.
.

This is incorrect, the regulations require that the cpc is present at every point on circuits where ADS is used.

 

[Pete999]

Hi
Thanks for your reply , I am talking about my house not my friends friends house ! , the feed to the lights were also just 2 core flat , I fit a cpc to them a long time ago direct from the cpc bonding terminal next to the meter ,but did not think about the light switches , the kitchen and lounge light switches have a cpc they where put in when some workwas done there prob about 5 year ago .

cheers

BB

What size cpc did you use and why take from a BONDING conductor connection, ?

 

[telectrix]

What size cpc did you use and why take from a BONDING conductor connection, ?

it's also an earthing terminal (MET). better would be to connect to the earth bar in the CU in the correct point for the circuit. and, if not mechanically protected, should be min. 4mm, but that's a minor point.

 

[BettyBoop44]

it's also an earthing terminal (MET). better would be to connect to the earth bar in the CU in the correct point for the circuit. and, if not mechanically protected, should be min. 4mm, but that's a minor point.

Hi
Thanks for your reply , what would be classed has "mechanically protected" under the floor boards ! , that is were I put the 2.5mm² cpc run , crikey I would not of liked to have tried to put 4mm² to my light fittings , the ceiling would of come down with the weight of the copper lol .
anyway thanks for your reply , great place to learn .
ps: by the way when did that reg come out 543.1.1 regarding the 4mm² , will feed it into my CU , has been recomemended , where I have it fed from now is the same point my CU is fed from ! .

BB

 

[westward10]

I have just found the same Reg 543.1 in my 1981 Fifteenth Edition but it has been around longer than that.

 

[Pete999]

Hi
Thanks for your reply , what would be classed has "mechanically protected" under the floor boards ! , that is were I put the 2.5mm² cpc run , crikey I would not of liked to have tried to put 4mm² to my light fittings , the ceiling would of come down with the weight of the copper lol .
anyway thanks for your reply , great place to learn .
ps: by the way when did that reg come out 543.1.1 regarding the 4mm² , will feed it into my CU , has been recomemended , where I have it fed from now is the same point my CU is fed from ! .

BB

2.5 protected i,e, in conduit or trunking, yes the MET is electrically connected to the earth bar in your CU but it is recommended that cpcs are connected in the CU

 

[BettyBoop44]

2.5 protected i,e, in conduit or trunking, yes the MET is electrically connected to the earth bar in your CU but it is recommended that cpcs are connected in the CU

Hi
Thanks again for your help , just one more and I will leave you alone , if I was to get a EICR for my house would they not pass it , if they had seen the 2.5mm2 cpc I put in the ceiling void to the lights ! .

 

[westward10]

Hi
Thanks again for your help , just one more and I will leave you alone , if I was to get a EICR for my house would they not pass it , if they had seen the 2.5mm2 cpc I put in the ceiling void to the lights ! .

Depends how clued up the person is doing the inspection.

 

[BettyBoop44]

2.5 protected i,e, in conduit or trunking, yes the MET is electrically connected to the earth bar in your CU but it is recommended that cpcs are connected in the CU

Hi
Thanks again for your help , just one more and I will leave you alone , if I was to get a

What size cpc and what routing did you take when installing he seperate cpc as there are regulations governing what should be done

Hi
From the MET straight up into the loft then through each floor joist to each light ! , going to put it into the CU earth bar instaed of the MET .

cheers

 

[Pete999]

http://www.electricalsafetyfirst.org.uk/mediafile/100404922/Best-Practice-Guide-4-Issue-4.pdf
Give it a C3 possibly C2 is about all I could recommend from a distance

 

[BettyBoop44]

I have just found the same Reg 543.1 in my 1981 Fifteenth Edition but it has been around longer than that.

Thanks for that , looks like I am going to have to change the 2.5mm2 to 4.0mm2 to the lights mam a mia , that was a job and a half putting in the 2.5mm2 from what I can remember , but you can't have enough supplimentry bonding in the house and I have a lot , water n gas pipes were I have been able to get to them , I hink there is more copper in the cpc's around the house than in Zambia ! .

cheers guys and thank you all for your comments and help .

BB

 

[Pete999]

Thanks for that , looks like I am going to have to change the 2.5mm2 to 4.0mm2 to the lights mam a mia , that was a job and a half putting in the 2.5mm2 from what I can remember , but you can't have enough supplimentry bonding in the house and I have a lot , water n gas pipes were I have been able to get to them , I hink there is more copper in the cpc's around the house than in Zambia ! .

cheers guys and thank you all for your comments and help .

BB

If you are going to access the routes to the lighting points why not run a new twin and cpc cable? sounds like you have been bunging supplementary bonding every where, has the pipework been tested to see if it actually requires bonding?

 

[telectrix]

i'd give the 2.5mm cpc a C3,

 

[davesparks]

Thanks for that , looks like I am going to have to change the 2.5mm2 to 4.0mm2 to the lights mam a mia , that was a job and a half putting in the 2.5mm2 from what I can remember , but you can't have enough supplimentry bonding in the house and I have a lot , water n gas pipes were I have been able to get to them , I hink there is more copper in the cpc's around the house than in Zambia ! .

cheers guys and thank you all for your comments and help .

BB

Was all that bonding actually necessary? Bonding things which don't need it can potentially increase danger rather than reduce it.
It would be far better to rewire the circuit than run an additional cpc, the old cables are likely to be getting towards the end of their expected lifespan of they aren't past it already.

What Zs readings did you get when you tested the 2.5mm cpc?

 

[BettyBoop44]

Hi
Thanks for your reply, yes you are right am going to rewire all the lower floor lights and switches , to be honest I was thinking of doing just that , just needed someone to push me to do it .
Best regards
BB

 

[BettyBoop44]

Thanks for all your feedback again have decided to rewire the lower lights n switches , my next question is what is the recomended csa of the cable to use ! .
ie 1.omm2/1.5mm2 / 1.5mm2 for radial n 1.00mm2 to switches ! .
cheers

BB

 

[davesparks]

Thanks for all your feedback again have decided to rewire the lower lights n switches , my next question is what is the recomended csa of the cable to use ! .
ie 1.omm2/1.5mm2 / 1.5mm2 for radial n 1.00mm2 to switches ! .
cheers

BB

The recommended size is the size which you have calculated using the information in your regulations book.
Mixing cable sizes in a simple installation is unnecessary, calculate thencable size required for the circuit and stick to that size throughout the circuit.

 

[BettyBoop44]

Was all that bonding actually necessary? Bonding things which don't need it can potentially increase danger rather than reduce it.
It would be far better to rewire the circuit than run an additional cpc, the old cables are likely to be getting towards the end of their expected lifespan of they aren't past it already.

What Zs readings did you get when you tested the 2.5mm cpc?

Hi
Thanks for your reply , is there a need to check the Zs when there is a RCD in the circuit ! .
BB

 

[SparkyChick]

Hi
Thanks for your reply , is there a need to check the Zs when there is a RCD in the circuit ! .
BB

Yes, you need to meet the Zs requirements of the over current protective device protecting the circuit. Using the RCD for fault protection is a last resort if you can't meet the Zs requirements of said device, but in my opinion this should only be considered if you have a TT supply.

 

[davesparks]

Hi
Thanks for your reply , is there a need to check the Zs when there is a RCD in the circuit ! .
BB

Yes there is, otherwise how do you know that ADS has been complied with. Even if you are thinking of relying on an RCD then you still need to confirm the continuity and resistance of the cpc.

 

[mrloy99]

Spellchecker?

 

[Paul mccullagh]

Hi
You must put this label on the consumer unit with the circuit details!

 

[Octopus]

Hi
Thanks for your reply , is there a need to check the Zs when there is a RCD in the circuit ! .
BB

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