Ring Main Cable in Insulation

[Damian30]

Hi,

I've been laying some 2.5mm t&e in the accessible cavity of my conservatory dwarf wall to extend the main house socket ring for 3 x double sockets in the conservatory.

This cable sits 100mm into the cavity insulation. Am I right in thinking that unless it was in a duct, it needs to be downrated to 16amps. I'd expect there to be a minimal load in the conservatory, so will I be alright leaving it as is. I could get back into the cavity and put it in flexible conduit, although it will require a bit of effort to revive the window boards that have been temporarily fixed.

Also, I was going to add a MK Masterseal Plus single socket. Is it preferable to add this to the ring or take as a spur. I can do either but not sure whether there is enough room in these boxes to get the two cables connected into the socket.

Any views much appreciated.

Many thanks,

Damian

p.s. I will be looking to get a local electrician to make the final connections, etc.

 

[EFLImpudence]

I've been laying some 2.5mm t&e in the accessible cavity of my conservatory dwarf wall to extend the main house socket ring for 3 x double sockets in the conservatory.

We're not supposed to run cables in cavities for the reason you are asking.

This cable sits 100mm into the cavity insulation.

What does that mean?

Am I right in thinking that unless it was in a duct, it needs to be downrated to 16amps. I'd expect there to be a minimal load in the conservatory, so will I be alright leaving it as is.

13.5A if totally surrounded.
You can't really design a minimal load on a socket circuit.

Also, I was going to add a MK Masterseal Plus single socket. Is it preferable to add this to the ring or take as a spur.

It doesn't matter.

I can do either but not sure whether there is enough room in these boxes to get the two cables connected into the socket.

Do you mean three?

Please see other threads for getting electricians to sign off.
//www.diynot.com/diy/threads/earth-cable-route.413512/

 

[JohnW2]

I've been laying some 2.5mm t&e in the accessible cavity of my conservatory dwarf wall to extend the main house socket ring for 3 x double sockets in the conservatory. ... This cable sits 100mm into the cavity insulation. Am I right in thinking that unless it was in a duct, it needs to be downrated to 16amps.

If its actually burried within that insulation, it would probably need to be downrated to 13.5A.

I'd expect there to be a minimal load in the conservatory, so will I be alright leaving it as is.

It doesn't work like that. The cable of all of a ring has to have a current-carrying capacity of at least 20A, regardless of local loads.

I could get back into the cavity and put it in flexible conduit, although it will require a bit of effort to revive the window boards that have been temporarily fixed.

I'm a bit confused by the regulations here. On the face of it, although the CCC of 2.5mm² T+E has to be de-rated to 13.5A if it is buried in insulation, it would seem that it's CCC becomes 20A if installed "in conduit in an insulated wall" - which (although that would be OK for a ring) does not really make sense to me.

p.s. I will be looking to get a local electrician to make the final connections, etc.

You need to speak to the electrician about these issues now - otherwise (s)he may not be happy to connect, let alone certify, the new work.

Kind Regards, John

 

[bernardgreen]

Also, I was going to add a MK Masterseal Plus single socket.

If this is an outside socket then best practise is to feed it as a spur via a double pole isolator ( FCU ) inside the conservatory. This will enable the ring to remain in use if the outside socket is damaged / water logged and thus causing the RCD to trip.

Also note the comments about running cables in the cavity of a cavity wall,

 

[Damian30]

Thanks chaps for feedback - think I get the gist of cables in a cavity.

If I was to put the cables in the cavity in say a 20mm or 25mm flexible conduit, would that be more acceptable?

 

[EFLImpudence]

I'm a bit confused by the regulations here. On the face of it, although the CCC of 2.5mm² T+E has to be de-rated to 13.5A if it is buried in insulation, it would seem that it's CCC becomes 20A if installed "in conduit in an insulated wall" - which (although that would be OK for a ring) does not really make sense to me.

Yes, I agree.

Is it supposed that the conduit is fixed to the wall or stud (not actually surrounded by the insulation as method 1 and 2 of table 4A2) and may be metal?
Whilst it doesn't say that, are we supposed to know?

 

[JohnW2]

I'm a bit confused by the regulations here. On the face of it, although the CCC of 2.5mm² T+E has to be de-rated to 13.5A if it is buried in insulation, it would seem that it's CCC becomes 20A if installed "in conduit in an insulated wall" - which (although that would be OK for a ring) does not really make sense to me.

Yes, I agree. Is it supposed that the conduit is fixed to the wall or stud (not actually surrounded by the insulation as method 1 and 2 of table 4A2) and may be metal? Whilst it doesn't say that, are we supposed to know?

As you will recall, that's the very question I've asked several times, most recently just a few days ago - and no-one has yet really offered an opinion, let alone answer. As we've both said, the diagrams for Methods 1 and 2 show the conduit touching the inner leaf of the wall - but nowhere (not even in that Table) do the descriptions of the insulation methods mention that as a requirement for the methods concerned - so it's really anyone's guess as to what is intended!

As I implied, common sense would seem to suggest that cable within conduit which is totally within insulation would have at least as low a CCC as the same cable buried within the insulation without conduit.

Kind Regards, John