Lighting with no CPC and installing new CU (Domestic)

[sparkshower]

Hi

so in this case then if the board is to be changed with the necessary labels/warnings and the correct fittings etc etc to get around the obstacle of metal backboxes that could be earthed what is the normal process here?

Is it required to test (long lead) between the metal screws/backboxes before having to change the screws to nylon ones, also are the switches with the screw covers acceptable to avoid the issue, (what if these fall off over the years)

thanks in advance

 

[morph]

An RCD works by detecting a difference between the currents flowing in the Line & Neutral conductors of a protected circuit, it doesn't care what creates that imbalance! Of course, an earth fault will cause an imbalance of currents but so will shared neutrals being fed from different sides of a dual RCD.

Hence providing a path for current to flow from either of the live pins in a plastic light fitting by sticking your finger in it while stood in the bath is likely to trip an RCD (but you try it rather than me :cheesy: )

if there was a shared neutral the rcd would trip before the lights even came on , so there would be no electric so yes that is safer but also useless

 

[morph]

No, I really don't see your point!
A light pendant with bayonet fitting has two round pins that can have 230V on at least one of them at times.
When there is no bulb in the fitting, they are exposed.

i see what you are saying but that has a flaw too
the two pins must be pushed in with reasonable force before contact is made
the case here is that a rcd will make the install safer
well it wont if the fittings are plastic and there is no earth its simple science
you probably think i am stupid , actually you could'nt be more wrong, not trying to be smart either just pointing a basic fact that so many people do not understand

 

[SJD]

Is it required to test (long lead) between the metal screws/backboxes before having to change the screws to nylon ones, also are the switches with the screw covers acceptable to avoid the issue, (what if these fall off over the years)

I guess it could be possible the backboxes are earthed some other way e.g. via conduit, and testing would establish that they are not, though in the case that prompted me to start this thread, I already knew they were not.

I still have a slight unease about nylon screws or screw covers, they can quite easily be changed or lost by someone who does not appreciate the electrical reason they were there. For example, while decorating, removing the switch from the wall, then having lost the screws, replacing with metal ones and putting one through L or N as it is done up. From the earlier posts, I think in practice, people are saying this solution is good enough.

 

[morph]

if the conduit is earthed then what is your problem ?
bit worrying this thread now

 

[telectrix]

you may well find that the lugs in the back boxes are nylon. this would eliminate the need for nylon screws.

 

[SJD]

i see what you are saying but that has a flaw too
the two pins must be pushed in with reasonable force before contact is made

So I just took two brand new pendant / ceiling rose prewired light fittings from my stock, one MK, one another brand, and tested resistance from the pins to the L and N terminals in the ceiling rose. In both cases, the pins are just connected, NO force is needed to make the connection.

 

[Octopus]

you may well find that the lugs in the back boxes are nylon. this would eliminate the need for nylon screws.

And you might find that the home owner throws you out for going OTT.

If the home has survived without a CPC, with class 2 fittings for 30 years then just get on and change the CU. Comments - lighting circuit doesn't have a CPC, add no CPC label to CU. Cert, invoice and notify.

All this chat about nylon screws etc is way OTT.

 

[morph]

So I just took two brand new pendant / ceiling rose prewired light fittings from my stock, one MK, one another brand, and tested resistance from the pins to the L and N terminals in the ceiling rose. In both cases, the pins are just connected, NO force is needed to make the connection.

still dont make it safer with rcd , if the plumbing is plastic or if the resistance is above 1667 then the rcd would not operate in time, plus basic and fault protective measures are defined as someting along the lines of " fault free and single fault etc"
well standing on a bath and sticking your fingers in a fitting is neither
its a cop out to say that a rcd is going to make it safer
i would fit the new board and say its for money .... not some untrue reason that does not hold up...
just pointing something out to you , no need to get all defensive

 

[oldtimer]

I agree with morph just move on you have to be pragmatic here many many years ago it was acceptable to install lighting circuits without a cpc so fast forward to today yes we have new or updated regulations but you need to grasp that you cannot back date the regs and that the new regs have to accomodate the older wiring systems . Also individuals on this forum think they are on some sort of religious mission to convert and insist that the customer must get the circuit rewired but at the end of the day all they can do is advise them that if they dont want to rewire then they need to use class II equipment we under the present regs and laws we cannot force them to sort it.

Now as for legalities we are seen as legally technically competent person or in other words we should know better so although Joe Public can put a class I light up we cannot and yes it can be frustrating but as I said previously yes I have lost the job but I or you cannot be the electrical policeman for your area