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.