Light Switch Back Boxes with no earth terminal

[charlie76]

I am working in a property that has the old steel painted switch back boxes that have no earth terminal. Came to light when testing R2 on the switch faceplate screws and got open circuit reading. Earth is present but just sleeved and folded over in the back box.

I intend to ring crimp the earth and clamp it under the fixing screws holding the back box into the brickwork, removing paint under the ring crimp to give good conductivity. Tested one and got a good R2 reading on the screws. Is this an acceptable method, obviously I don't want to start ripping boxes out the wall to install new galv back boxes.

 

[telectrix]

or you could replace switches with metal facepates and use the earth terminal in the new faceplate. the 3.5mm pins would then give you an earth to the box.

 

[westward10]

I wouldn't put them under back box screws it isn't an earth terminal. Some back boxes have four lugs for front plate fixing and you could use one of them or drill and tap the back boxes but the brickwork gets through the drill bits. The previous Post to this is an excellent solution.

 

[Sintra]

Or if they are plastic faceplates you could use nylon 3.5mm screws.

 

[westward10]

Or if they are plastic faceplates you could use nylon 3.5mm screws.

This is true until someone loses one and sticks a metal one in.

 

[Deleted member 93172]

If there is only 2 face plate fixing holes, then terminating the earth via a lugg to the box fixing screw is the only way unless you change the back box.

 

[charlie76]

If there is only 2 face plate fixing holes, then terminating the earth via a lugg to the box fixing screw is the only way unless you change the back box.

Yes, there are only 2. So would you comment on this under condition of existing system on the EIC and state what solution I have provided?

 

[westward10]

Yes, there are only 2. So would you comment on this under condition of existing system on the EIC and state what solution I have provided?

I would C3 that the cpcs are terminated under back box fixing screws. I would drill and tap them.

 

[telectrix]

Or use a self drill screw with lug on cpc. OK if masonry behind box is soft.

 

[HandySparks]

I would C3 that the cpcs are terminated under...

It's an EIC not an EICR.

 

[charlie76]

I can't to find a reg which would not permit what I am proposing. 134.1.4 seems ok and 526 i dont see anything there.

 

[telectrix]

I can't to find a reg which would not permit what I am proposing. 134.1.4 seems ok and 526 i dont see anything there.

what about the fixing screw rusting over time and creating a high resistance contact. even if i say so myself. my post suggesting metal faceplates is a good solution and also improves the aesthetics. win win.

 

[freddo]

Most of the black painted switch boxes around here have plastic lugs so is not a problem, I take it yours have metal lugs though?

There is a reg which says a fixing screw can't double as an earth terminal, though I've no Idea which one. If the box gets knocked it could loosen the connection etc. Unlikely with a recessed box though. In the stores we have a load of MK earth terminals that would do the job, though the box would have to be removed from the wall to do it by which point it would be easier to replace the box!

 

[charlie76]

what about the fixing screw rusting over time and creating a high resistance contact. even if i say so myself. my post suggesting metal faceplates is a good solution and also improves the aesthetics. win win.

Brass / Stainless Screw? I'm not knocking your idea though probably the best solution although costly.