When are fly leads necessary?
- Thread starter Jupiter01
- Start date
You'll probably get varying responses, but it certainly seems like a fairly good idea, and certainly won't do any harm.
The important thing is that the metal faceplate must be connected to earth. When the socket is 'in situ', that should result in the backbox (assuming it is metal!) being earthed via the faceplate screws, but there is a theoretical 'risk' for any idiot who undoes the screws and pulls the socket forward whilst the circuit is still energised. A flylead from the socket's earth terminal to the backbox solves that problem.
Of course, if backbox/whatever is plastic (surface pattress or 'plasterboard' box), there is nothing to earth, so no point in a flylead (even if the box has an 'earth terminal'.
Kind Regards, John
I'd suggest always using one as good practice rather than relying on the faceplate screws always being tight.
Lost count of the number of calls I've had from tutors to say they were unplugging some piece of equipment and the socket feels loose.
Just need the faceplate screws tightening, and this is in a £34m new building less than 2 years old.
Lost count of the number of calls I've had from tutors to say they were unplugging some piece of equipment and the socket feels loose.
Just need the faceplate screws tightening, and this is in a £34m new building less than 2 years old.
Some people have opinions that they believe to be sensible.
Common sense is to ensure a metal back box is earthed at all times. Why is it common sense ?.
If the insulation of a conductor is penetrated by a sharp edge of the metal back box then the back box could become Live if not connected to the CPC ( earth wire ). That is obviously a hazard to someone who removes the front plate. Not so obvious is that any dampness in the wall around the Live metal back box will conduct the Live potential from the metal back box to the surface of the wall.
So would I, but ....
Unless the faceplate screws are dramatically 'loose' (to the extent that one can get one fingers behind the faceplate and touch the backbox, having a backbox which is poorly (or not at all) earthed because of loose faceplate screws is not a hazard to anyone, is it?
Kind Regards, John
It depends.
As I understand it, if the backbox has at least one fixed lug (most do) and the accessory is designed to earth the fixing screws (most accessories with an earth terminal are). then the IET deem this to be adequate for earthing the backbox from the accessory. However the reverse is not true, for systems where the where the protective conductor is formed by a metal enclosure an explicit flylead to the accessory is required.
Even plastic sockets require earthing, so sockets should simply be a straight swap.
On the other hand, plastic switches do not have earth terminals. So when replacing plastic switches with metal ones you need to take more care. Modern regulations require an earth to be taken to every accessory even if it doesn't need it, so it should be a simple matter of adding a flylead or moving the wires from the backbox earth terminal to the accessory earth terminal. However very old installations may not have earths on the lighting at all and bodged installations may have not bothered to connect it. So IMO earth connection to switches should be verified before considering replacing plastic switches with metal.
Plastic switch, metal back box with no earth, damaged insulation in the back box, metal face plate screws, worst case the heads of the screws are at Live potential.
Solution can be to use nylon screws or fit screw caps ( as supplied with some switches )
I'm not sure that the plastic caps are designed to be used for this purpose though, since they can fall out - so I think they are for decorative purposes only.
The nylon screws situation is sound though - 60 years ago metal switch boxes tended to have nylon lugs, in which metal screws were put into - which to me equates to using nylon screws as you describe.
Any loose screws should be avoided because they are poor connections.
As Bernard says, if the back box becomes live, through whatever reason, there is the potential for the faceplate screws to become live, even if they are loose.
However, on a plastic surface mounted pattress, with a regular plastic light switch (ie no earth terminal on the switch) there is a possibility the faceplate screws could become live if someone pinches a wire whilst sctrewing the faceplate back.
I think we had better stop using electricity.
Fossil fuels is the way to go right?
Even though we were not talking about that (plastic faceplates), I had rather suspected that you would come up with that one
I was responding to a comment about 'loose' faceplate screws and unless they are loose to the extent of protruding from their recess, that (incredibly small) theoretical risk is almost as 'high' with non-loose screws than with 'loose' ones.
It could be, but have you ever heard of an electrician who routinely uses nylon screws with plastic accessories (on metal back boxes), or seen an installation where that has been done?
I would have thought that it would be incredibly improbable that something which made a backbox 'live' would happen 'spontaneously' after the accessory had been pushed back into the box (and the screws tightened). That being the case, it would require that neither of the faceplate screws were tight enough to establish electrical contact with the box for an OPD not to operate when the circuit was initially energised, which would, again, be incredibly unlikley - even a 'loose' screw is pretty likely to establish electrical continuity .
As always, it's a matter of "every man to his own", and we know that some are incredibly risk-averse. I personally do always use flyleads, but really only to avoid the possibility of someone moaning about their absence in the future, not because I am concerned about a minute theoretical risk.
What I don't favour (but have often seen) is terminating the incoming CPC to a backbox terminal and then having a separate flylead connecting that terminal to a socket or an accessory with a metal faceplate - since that involved inserting an unnecessary joint in the COPC's path to "where it is mainly needed".
Kind Regards, John
As I've said, it depends upon how ultra-cautious one wants to be, and it's not for me to knock the ultra-cautious.
It's pretty difficult (probably even for children) to touch the head of a faceplate screw in a plastic accessory (particularly if it has been tightened enough to damage insulation in the manner you describe) and, even in the extremely unlikely event of the screw being 'live', one would be very unlucky to not only manage to do that but also to find something else earthed to touch simultaneously.
Kind Regards, John
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