Adding lights to circuit with no CPCs

[harrymonkfish]

Hi there.

I have been asked to add some downlights to a lighting circuit with no cpcs.

The circuit is rcd protected and he wants elv lights.

Can i just add them because they are elv or do the same rules apply as for lv?

any suggestions greatly appreciated.

harry

 

[iansparks]

been asked this question a few times, Providing it is marked on the Certificate that the circuit does not have a CPC and only Class 2 fittings, switches are to be used.

Place the sticker "this circuit contains no CPC.... on the consumer unit

and only install class 2 fittings your okay

Admittadly - not ideal but your covering yourself if the customer wont pay for circuit re-wire, Lets face it, if you wont do it, someone else will and might install metal fittings on circuit

 

[Phil Mumford]

Agree will electricAL here.

We should have the freedom to use other forms of protection.

Think SAFETY. What are the risks? Mrs X climbs a ladder and grabs the fitting only to fall to her death? This can be easily avoided.

The light fitting cannot be allowed to become live without some means of ADS if the risk of indirect electric shock exists. How do we do this?

Many ways to achieve this:

• Plastic fittings (double insulated) and required notices with reduced periodic inspection notice. RCD protection and introduce 12 monthly 3rd party RCD tests.
• Convert to SELV, OK the mains wiring has no earth - who cares? No real risk of shock if cables are concealed and switches are LV side too. RCD protection and introduce 12 monthly 3rd party RCD tests.
• System of limited periodic testing (say 1 year) for the unearthed lighting wiring checking insulation resistance as a priority. RCD protection and introduce 12 monthly 3rd party RCD tests.
• All of the above.

All the above would only be carried out with agreement/instruction of the client but it would be SAFE. Far safer than some of the crap I come across.

I am not a believer in earth-free installations but combined with modern RCD's/RCBO's they are as safe as ... .. er... . . houses !

 

[Spudnik]

An RCD is not permitted to be used as the sole means of protection.

Also, whilst you can change a CU with no CPC in a lighting circuit, ad label the CU accordingly and use Class II fittings, it DOES NOT absolve the installer from responsibility should a problem occur.

 

[electricAl]

Just for the record, even if Harry was intending to use SELV (reasonable assumption really) i wasn`t suggesting he ought to ignore the lack of cpc in supply cct - as i wrote in my first post...

Not seriously suggesting he should do it , but...

...too many echoes of `can i get away with just making the bit i`ve done compliant?`
Lets not have that one again, eh.

Even tho i don`t believe tacking on a SELV cct would make the installation any less safe, i still wouldn`t do it myself.


I responded directly to the raising of Reg 411.3.1.1 - which doesn`t apply in the case of SELV or other situations - so was being quoted out of context

However, it most definately does apply for the supply on the primary side

 

[Davey101]

However, it most definately does apply for the supply on the primary side

So are you saying that this arrangement would not be acceptable?
T+E into a plastic JB which also has a 12volt tranny connected into it. I then run a 2 core cable to another plastic JB which has another tranny, and so on.

Are the regs really insisting that we must run a cpc in, and connect it to nothing but itself?

My take on it is that, if you so desired, you could run a 2 core flex (of the correct size) from a light switch to a ceiling full of selv (as long as the tranny is double insulated as well) or double insulated light fittings. Whether thats a good idea or not is another question, but I cant see how its against regs.
I was about to say-
"I cant see how a cpc protecs a cable either, if you damage the insulation and the live core is exposed, having an earth inside the cable wont help you one bit. If you cut right through the cable, then you have short circuit protection."
However, thinking about it, if you had a cable with no neutral, or earth,i.e a 3 core used for strappers, then cutting the cable would not result in ads.
Is there a reg to say all cables must have a integral cpc?

 

[electricAl]

So are you saying that this arrangement would not be acceptable?
T+E into a plastic JB which also has a 12volt tranny connected into it. I then run a 2 core cable to another plastic JB which has another tranny, and so on.

No Davey, not saying that atall - thats fine. The problem with the OPs proposed job was that it wasn`t a T&E supplying the TX - it was Twin & NoEarth - aka 2 core

Are the regs really insisting that we must run a cpc in, and connect it to nothing but itself?

In the case of SELV, certainly not. If you re-read post #15 you`ll see i`ve tried to clarify the distinction made between the various forms of `Protective Measures`. If the chosen method is SELV, a cpc can ONLY run to the end of Primary side - no connection to earth would be required nor permitted within the SELV cct itself.

My take on it is that, if you so desired, you could run a 2 core flex (of the correct size) from a light switch to a ceiling full of selv (as long as the tranny is double insulated as well) or double insulated light fittings. Whether thats a good idea or not is another question, but I cant see how its against regs.

Indeed ,you could argue that, provided that the switch was cpc`d then all beyond it (inc switch to tx cable) is not required to be connected to earth. But whilst i agree the Regs fail us on this point, we would, of course, generously provide protection by ADS - by including a protective conductor within that wiring system (e.g T & E)
Obviously, beyond point of connection to Double Insulated tx (Protective Measure in itself) the wiring system (2 core cable) would not require a cpc due to the Protective Measure of SELV.
But you couldn`t rely on Class II fittings alone as a Protective Measure, as you couldn`t ensure they don`t get swapped for Class I
Hope thats understandable enough...

was about to say-
"I cant see how a cpc protecs a cable either, if you damage the insulation and the live core is exposed, having an earth inside the cable wont help you one bit.

True enough if you don`t simultaneously contact the cpc - ouch!

If you cut right through the cable, then you have short circuit protection."

you sure do - thru the neutral or earth return paths.

However, thinking about it, if you had a cable with no neutral, or earth,i.e a 3 core used for strappers, then cutting the cable would not result in ads.

Quite, thats why we use either earthed wiring enclosers or 3 core & earth.
& cheat with RCDs
But if your point relates to ...

Is there a reg to say all cables must have a integral cpc?

...then obviously there couldnt be

 

[Davey101]

No Davey, not saying that atall - thats fine. The problem with the OPs proposed job was that it wasn`t a T&E supplying the TX - it was Twin & NoEarth - aka 2 core

Thanks for the very good reply, I must learn how to multi qoute
Just to clarify, in my example, it wasnt a T+E supplying the TX, it was a two core flex (T+E to the first tranny, and two core flex to the primary side of the second and subsequent trannies). This means that the primary supply to all but the first tranny does NOT contain a cpc, either connected, or in the cable itself.

My point about running a cpc- "Are the regs really insisting that we must run a cpc in, and connect it to nothing but itself?" related directly to 240v supplies, I understand the requiremnets (or lack of) relating to selv earthing.
If we are saying that my example is satisfactory, then I do not see a problem with what the OP was suggesting.
If we are suggesting that my example is incorrect, then I had better rewire my downlighters in my living room

Not saying I am right, I'd like to know for the future if I've missed something about cpc regulations

I've just re-read your post, and I think you have answered my questions. Looks like we are agreed in principle at least.
Cheers, Dave.

 

[electricAl]

I've just re-read your post, and I think you have answered my questions. Looks like we are agreed in principle at least.Cheers, Dave.

Glad we got there eventually

Harrys proposal & your example had one telling difference - you supplied a cpc to the switch controlling the SELV protected tx (when using ADS - "a cpc shall be run to ...each point ...& accessory)

Harry could not

Al