Earthing sockets and switches

[henryb1]

Hi
I have recently changed my socket and light switches in my home. I thought that i had earthed them properly. However after watching a DIY show last something has worried me. I have connected the earthing wire to the earth terminal on the switchs / sockets instead of the terminal on the casing. IS THIS SAFE????

 

[dingbat]

The circuit protective conductor (the bare wire that sits in the sheath along with the live and neutral) should go directly to the socket's earth terminal - this ensures that anything plugged in has a direct earth connection. In addition, you can run a short connection between this point and the galvanised backbox, although this is not strictly necessary if the backbox has at least one fixed lug.

Any exposed metalwork needs to be similarly earthed - most metal sokets are earthed via the main socket earth terminal. In 'Bricking It' last night, the lad was wiring up metalclad sockets - for these you should run an extra connection between the socket earth and the backbox earth as a matter of course.

 

[henryb1]

so is it safe to leave my sockets the way they are? but what about the light switches do i earth the sitch or the box then?

thanks for your comments

 

[dingbat]

I haven't seen your acessories, so how can I say for certain?

With most modern accessories the earthing of the faceplate (if metallic) is integral with the main earth terminal of the socket. If this is the case and you've sleeved the earths with green/yellow oversleeving, that's sufficient.

With switches there will be an earth terminal on metal switchplates - use that one. If plastic (which won't have an earth terminal) then you should use the backbox earth terminal and if there isn't one of these you should use a section of terminal strip ('chocbloc') to terminate the earth/s

In short, every piece of exposed metalwork which forms part of the electrical installation should have a reliable earth connection. Why? Because if a fault causes this exposed metal to become live (trapping a live cable with the accessory screws, for instance, a loose connection, etc...) the earth path back to the consumer unit will be of sufficiently low resistance to melt the fuse or trip the breaker and disconnect the circuit. Without this alternative circuit path a fault could make exposed metalwork stay live... until you discover it.

 

[jenki]

Hi
However after watching a DIY show last something has worried me.

Yeah Saw the same program "Bricking It" C4, the install was surface mounted Galv conduit, with metal back boxes, metal clad switches wired in singles -(For a modern apartment) I was quite surprised that the supervisor told the kid that it was extremely dangerous. From what i could see the cpc was connected to the switch plate and not the back box.

Is this install method different Or can you allow the plate screw to earth the back box (if it has a fixed lug).

 

[henryb1]

my switches / sockets are chrome plated with what seems like metal back boxes

 

[dingbat]

Yeah Saw the same program "Bricking It" C4, the install was surface mounted Galv conduit, with metal back boxes, metal clad switches wired in singles -(For a modern apartment) I was quite surprised that the supervisor told the kid that it was extremely dangerous. From what i could see the cpc was connected to the switch plate and not the back box.

Is this install method different Or can you allow the plate screw to earth the back box (if it has a fixed lug).

With a sunken back box, none of it is visible and it is therefore not exposed unless you are working on it, when it shouldn't be live anyway. With all exposed metalwork (in this case the metalclad box) you have to ensure that the earth connection is effective and the best way to do this is to run a bit of x-grade single yellow/green between the accessory earth terminal and the back box terminal. (If in doubt, connect up any earth terminals in sight!)

As far as being extremely dangerous, that's debatable. I thought I saw a connection to the box, but the comments might well have been staged for camera. Or over-emphasized to get the message across.