Earthing Metal Back Boxes- what size cable to use ?

[ahll]

Hi All,
Does anyone know when you earth a metal back box if it matter what size earth cable you use ?

For sockets I tend to use 2.5mm but should anything different be used for sockets that will take larger cable e.g. a 45amp switch for a cooker or Shower ?

 

[planemad]

Use whats in the cable, just sleeve it.

 

[ColJack]

he means the fly lead to the metal backbox from the earth on the front plate.

 

[ahll]

Yes I have noticed that the connector in the back box doesnt take very large cables..so I was wondering if there was some regulations that stated what has to be used or if it does really matter as long as the back box is earthed. So 2.5mm is ok for any back box ?

 

[Taylortwocities]

I do not recall any specific regulations, in fact, the back box does not need o be earthed if one lug is fixed.

As good practice I always earth the back box, however.

I use conductor sized at least that of the cable. So for 2.5mm T&E use minimum 1.5mm fly lead. I have a reel of 2.5mm single green&yellow and tend to use that as it is multicore (so flexible) and comes ready sleeved!

 

[dainesekid]

I also thought that they didnt need earthing in order to comply with regs ?

 

[ahll]

I also thought that they didnt need earthing in order to comply with regs ?

I did to thats why I have made sure all of them are !

 

[mattylad]

Planemad's reply was what I assume is the most common DIY way of doing this.

Just use the earth/cpc core from in a bit of 2.5mm T/E cable & G?Y sleeve it.
Unless you also have some G/Y cable then surely this should be fine.

 

[Spark123]

If the box isn't accessable and it is sunk into the wall, it has one fixed lug and there is the facility on the accessory to earth it then the link may be ommitted, however just for old time sake I tend to put them in anyway. Just use a piece of 1.5mm earth stripped from 2.5mm twin and earth.

If the box is accessable such as a metal clad one then the link must be installed. The link can be sized using the adiabatic equation which is the reason a 1.5mm CPC is allowed in a circuit protected by a 32A MCB.