Earthing Question

[jazzyb88]

Hi,

I am about to replace a 1 gang plastic switch with a 1 gang brass dimmer switch. The mounting box is metal and has two earth wires going into it. Since i need to earth the face plate, i understand i need to run a single cable from the face plate to the mounting box.

However, i was wondering whether you could 'split' up the two earth wires, and have one going to the face plate and the other going to the mounting box. I'm not sure why you cannot do this?

Cheers.

 

[Spark123]

No - one earth will likely be the earth from the supply and the other to an accessory or something. They need to remain connected together, you may use a link so you have two earths in each terminal. You may put all 3 into the backbox earth and loop to the front plate, likewise you may put all 3 into the front plate and link to the back box (maybe better if all 3 wires will fit as the switchplate earths are often a better quality terminal).

 

[jazzyb88]

Hi Spark123,

Thanks for that bit of useful information . In light of that information, i have another 1 gang wall socket with twin earth connectors. I trust it would be okay to take the two earth wires out of the mounting box, put both of them in one of the earth terminals in the plastic face plate, and then run another earth from the second earth terminal of the face plate back to the mounting box?

Cheers.

 

[Spark123]

Yep
It is arguable wether or not the link is actually needed when the backbox is sunk and has at least one fixed lug as the backbox should be earthed via the mounting screws, however I tend to put them in as I consider it good practice.
You should never rely on earthing the back box to earth socket front via the mounting screws tho.

 

[jazzyb88]

Thanks for confirming! I recall reading the same - screws can be changed out or corrode which reduces their effectiveness.

Thanks again.