Socket Backboxes Back-to-Back

Ben1989

I have two sockets that are literally back-to-back and connected via a stud and nuts.

Is this okay/safe?

grumbler

I don't understand how they are fixed and why the stud and the nuts are needed. Usually it's the plasterboard that holds a backbox.
If they are fixed reliably, I don't see anything unsafe. 

Section62

grumbler said:

I don't understand how they are fixed and why the stud and the nuts are needed. Usually it's the plasterboard that holds a backbox.
If they are fixed reliably, I don't see anything unsafe. 

Could be in a solid wall?

My question is whether the two backboxes are metal (conducting) or plastic (insulating) and the extent to which a (presumably) metal stud between them may compromise electrical safety - e.g. if one end came into contact with a live conductor in one box resulting in a live and unearthed metal object being present in the second box.

JohnB47

Ben1989 said:

I have two sockets that are literally back-to-back and connected via a stud and nuts.

Is this okay/safe?

I'm not a qualified electrician but to my mind this is not a problem if:

The boxes are secured properly (did you mean bolts and nuts?) not just together but plastered into the recess too. So all nice and rigid. Ideally, but not perhaps essentially,  an earth strap would be fitted so as to connect both boxes earths together. Obviously the earth wires in the cables coming into each box would be terminated in their box too.

If everything is secure and comprehensively earth strapped together, I can't see a problem.

Section62

JohnB47 said:

If everything is secure and comprehensively earth strapped together, I can't see a problem.

It could be a problem if the two boxes are on different circuits and not meant to be "earth strapped together".

Possibly unlikely that is the case, but without much more information it is impossible to rule out.

grumbler

Section62 said:

JohnB47 said:

If everything is secure and comprehensively earth strapped together, I can't see a problem.

It could be a problem if the two boxes are on different circuits and not meant to be "earth strapped together".

Can this be found in domestic wiring?

With two or more RCDs  neutrals do have to be separated, but not earths.

Section62

grumbler said:

Section62 said:

JohnB47 said:

If everything is secure and comprehensively earth strapped together, I can't see a problem.

It could be a problem if the two boxes are on different circuits and not meant to be "earth strapped together".

Can this be found in domestic wiring?

With two or more RCDs  neutrals do have to be separated, but not earths.

Anything can be found in domestic wiring. (not necessarily compliant with current regs)

Having more than one earthing system within one installation is not that uncommon. In which case care has to be taken to avoid accidental interconnection.

Ectophile

Section62 said:

grumbler said:

Section62 said:

JohnB47 said:

If everything is secure and comprehensively earth strapped together, I can't see a problem.

It could be a problem if the two boxes are on different circuits and not meant to be "earth strapped together".

Can this be found in domestic wiring?

With two or more RCDs  neutrals do have to be separated, but not earths.

Anything can be found in domestic wiring. (not necessarily compliant with current regs)

Having more than one earthing system within one installation is not that uncommon. In which case care has to be taken to avoid accidental interconnection.

You should never have two different earthing systems within touching distance of each other.  That's usually only a problem in commercial premises divided into individually metered units.  Most houses only have one supply.  It only really gets to be a problem when running supplies outdoors (sheds, hot tubs, etc.) when you need to think about what earthing system to use.

Apodemus

Ectophile said:

Section62 said:

grumbler said:

Section62 said:

JohnB47 said:

If everything is secure and comprehensively earth strapped together, I can't see a problem.

It could be a problem if the two boxes are on different circuits and not meant to be "earth strapped together".

Can this be found in domestic wiring?

With two or more RCDs  neutrals do have to be separated, but not earths.

Anything can be found in domestic wiring. (not necessarily compliant with current regs)

Having more than one earthing system within one installation is not that uncommon. In which case care has to be taken to avoid accidental interconnection.

You should never have two different earthing systems within touching distance of each other.  That's usually only a problem in commercial premises divided into individually metered units.  Most houses only have one supply.  It only really gets to be a problem when running supplies outdoors (sheds, hot tubs, etc.) when you need to think about what earthing system to use.

This is all good stuff, which I was previously unaware of.  Can you explain why two different earthing systems touching each other is a problem?  I would always have (wrongly it seems!) assumed that the more earthing the better!

fenwick458

Apodemus said:

Ectophile said:

Section62 said:

grumbler said:

Section62 said:

JohnB47 said:

If everything is secure and comprehensively earth strapped together, I can't see a problem.

It could be a problem if the two boxes are on different circuits and not meant to be "earth strapped together".

Can this be found in domestic wiring?

With two or more RCDs  neutrals do have to be separated, but not earths.

Anything can be found in domestic wiring. (not necessarily compliant with current regs)

Having more than one earthing system within one installation is not that uncommon. In which case care has to be taken to avoid accidental interconnection.

You should never have two different earthing systems within touching distance of each other.  That's usually only a problem in commercial premises divided into individually metered units.  Most houses only have one supply.  It only really gets to be a problem when running supplies outdoors (sheds, hot tubs, etc.) when you need to think about what earthing system to use.

This is all good stuff, which I was previously unaware of.  Can you explain why two different earthing systems touching each other is a problem?  I would always have (wrongly it seems!) assumed that the more earthing the better!

he didn't say 2 different earthing systems touching each other was the problem, the problem could be having 2 different earthing systems.
its potentially dangerous as you could get a potential difference between the 2, and if an unsuspecting person was to touch both at the same time, they would get a shock

Apodemus

fenwick458 said:

Apodemus said:

Ectophile said:

Section62 said:

grumbler said:

Section62 said:

JohnB47 said:

If everything is secure and comprehensively earth strapped together, I can't see a problem.

It could be a problem if the two boxes are on different circuits and not meant to be "earth strapped together".

Can this be found in domestic wiring?

With two or more RCDs  neutrals do have to be separated, but not earths.

Anything can be found in domestic wiring. (not necessarily compliant with current regs)

Having more than one earthing system within one installation is not that uncommon. In which case care has to be taken to avoid accidental interconnection.

You should never have two different earthing systems within touching distance of each other.  That's usually only a problem in commercial premises divided into individually metered units.  Most houses only have one supply.  It only really gets to be a problem when running supplies outdoors (sheds, hot tubs, etc.) when you need to think about what earthing system to use.

This is all good stuff, which I was previously unaware of.  Can you explain why two different earthing systems touching each other is a problem?  I would always have (wrongly it seems!) assumed that the more earthing the better!

he didn't say 2 different earthing systems touching each other was the problem, the problem could be having 2 different earthing systems.
its potentially dangerous as you could get a potential difference between the 2, and if an unsuspecting person was to touch both at the same time, they would get a shock

Ah!  Thanks!  Yes that makes sense.  So in the OP's case, it would be safest to make sure the earth wires for the two back-boxes are linked?