earthing a new double socket

[jammiebodger]

hi guys, novice here seeking advice,
in my garage currently there is a single double power socket. This runs on a single cable from the consumer unit (i.e not on a ring circuit).
when i took the face plate off the wall socket, there was one neutral, one live and one earth as expected. however, there are two points on the power outlet marked earth (with a common live and neutral) should both these earths be connected?
I now want to install a new double socket as a spur from the original plug. i have the same question about the earth cable. there are two points on the new wall plug marked earth, but i have only one cable!
Can i just link the two points together?
many thanks,
d

 

[SparkyTris]

yeah

 

[Taylortwocities]

The two earth points are already connected inside the socket. You do not need to join them together.

There is a big no-no in your plans.

The socket you already have is a spur off the ring. You can only change the existing (single) socket for one double socket.
You cannot add any more sockets unless you change the existing socket for a 13A fused connection unit. Then you can add as many as you like to the output of the FCU but your total output maximum current available will be 13A.

 

[xr4x4]

You only need to earth one point on the socket and earth the back box if its metal.

 

[JohnW2]

....in my garage currently there is a single double power socket. This runs on a single cable from the consumer unit (i.e not on a ring circuit).
when i took the face plate off the wall socket, there was one neutral, one live and one earth as expected. however, there are two points on the power outlet marked earth (with a common live and neutral) should both these earths be connected?
I now want to install a new double socket as a spur from the original plug. i have the same question about the earth cable. there are two points on the new wall plug marked earth, but i have only one cable!
Can i just link the two points together?

The two earth terminals in the sockets are provided only for convenience; as you may be able to see, they are solidly connected together, so you don't have to join them yourself with wire. You can use either (or both, if you wish, when there are two cables - as there will be in the first one when you add the spur).

If the sockets are mounted on metal boxes, don't forget that they need to be connected to earth (again, either of the terminals) as well.

Do you know what size cable is used to feed the socket, how it gets to the garage, what sized fuse/breaker it is connected to at the consumer unit and whether this circuit is protected by a 'RCD' in the consumer unit, and whether the circuit serves anything other than the garage? The answers to those questions may mean that some people will have other things to say.

Kind Regards, John.

 

[JohnD]

The socket you already have is a spur off the ring.

are you sure about that?

runs on a single cable from the consumer unit (i.e not on a ring circuit).

 

[riveralt]

If the sockets are mounted on metal boxes, don't forget that they need to be connected to earth (again, either of the terminals) as well.

Struggling to find that one in the red book John can you help out please!

 

[jammiebodger]

thanks for the replies,
the cable supplying the original double socket is about 2.5mm to look at. it runs right out of a blank on the right hand side of the consumer unit which is about a meter and a half away. this garage socket shares an isolation switch on the CU with the central heating (?spur) and its covered by a 30mA RCD.
Any more thoughts?
thanks,
d

p.s no metal boxes, plastic all round!

 

[JohnW2]

If the sockets are mounted on metal boxes, don't forget that they need to be connected to earth (again, either of the terminals) as well.

Struggling to find that one in the red book John can you help out please!

Is this a 'trick question', or some sort of game?! I can't really be bothered looking for it - I find it hard to believe it's not in the book but, even if it isn't, I will continue to expect (as, I imagine, everyone else does) that a metal backbox will be connected to the cpc.

Or are you perhaps quibbling about the word 'earth', or maybe 'metal box'? If so, bear in mind that I was responding to someone who described him/herself as a novice.

Kind Regards, John.

 

[riveralt]

Is this a 'trick question', or some sort of game?! I can't really be bothered looking for it - I find it hard to believe it's not in the book but, even if it isn't, I will continue to expect (as, I imagine, everyone else does) that a metal backbox will be connected to the cpc.

Not a trick question or a quibble over earth or metal box - I have been unable to find this is the red book - since you made the statement I assumed you had.
I believe this is optional and not necessarily a requirement.

 

[riveralt]

thanks for the replies,
the cable supplying the original double socket is about 2.5mm to look at. it runs right out of a blank on the right hand side of the consumer unit which is about a meter and a half away. this garage socket shares an isolation switch on the CU with the central heating (?spur) and its covered by a 30mA RCD.
Any more thoughts?

What size MCB is controlling this socket and the central heating circuit?
Also what size is the cable for the central heating circuit?

 

[jammiebodger]

sorry river, not too sure,
the (isolation) switch for the socket/heating says b32, nsb32.
then theres just the rcd 80A 30mA
not sure which supply exiting the CU goes to heating but all are around 2.5mm.
d

 

[riveralt]

For a radial circuit with 2.5mm T&E cable I would not expect the MCB to be more than 20Amps. Where the 2.5mm T&E is clipped direct to the wall or buried in plaster the current carrying capacity is around 27amps. The MCB rating must always be less than the current carrying capacity of the cable.
If you have a 32amp MCB then this is a problem and needs to be changed.
Also if you have both cables protected by the same MCB then the cables need to be the same size.

I would call an electrician out.

 

[JohnW2]

Not a trick question or a quibble over earth or metal box - I have been unable to find this is the red book - since you made the statement I assumed you had.
I believe this is optional and not necessarily a requirement.

OK. Maybe you are thinking of flush-fitting backboxes, in which case I can imagine it might be optional, provided that there is adequate provision for the faceplate screws to be in good contact with 'earth' without the backbox itself being 'earthed'.

However, given that we were talking about a garage, I was assuming that we would be dealing with a surface box. If so, would it not be an exposed-conductive-part, and therefore required to be connected to CPC per 411.3.1.1 etc?

Kind Regards, John.

 

[riveralt]

However, given that we were talking about a garage, I was assuming that we would be dealing with a surface box. If so, would it not be an exposed-conductive-part, and therefore required to be connected to CPC per 411.3.1.1 etc?

I know the OP has stated that he is using plastic - but it seems to me that the last part of 411.3.1.1 , 'A cpc shall be run to and terminated at each point in wiring and at each accessory, except a lampholder having no exposed conductive parts and suspended from such a point', implies that you must run a fly lead from the socket cpc to the earth point on the metal box.
Must add that one to the memory.