Insulating ground floor, what to do with cables?

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Got the floorboards up on our suspended ground floor.

Sleeper walls, airbricks, 4x2 joists, the usual setup.
Going to be insulating between joists with 4" rockwool.

Currently have 2.5mm T&E feeding 9 downstairs double sockets, with a spur for a single outside socket. The cables are currently clipped to sides of joists, so they will end up buried in the insulation.

I will replace all the cable runs like for like with new cable, what's the best way to route them? I have a few lengths of 20mm galv conduit available.

Could I clip these underneath the joists and run the t&e through them?

We get the occasional mouse/rat in the house so I don't want to leave the cable too exposed.

I have no bending facility and don't want to terminate the conduit into every socket box 'door to door', but just have the open end of the conduit beneath the floor within the vicinity of the socket.
 
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.... I have a few lengths of 20mm galv conduit available. ... Could I clip these underneath the joists and run the t&e through them? ... We get the occasional mouse/rat in the house so I don't want to leave the cable too exposed.
If you simply clipped the cables to the underside of the joists (no conduit) (which may well be possible, at least in many/most cases, without replacing the cables), they presumably would not be significantly more exposed to rodents than they are at present. Do I take it that you want to increase the protection against rodents as well as installing the insulation?
I have no bending facility and don't want to terminate the conduit into every socket box 'door to door', but just have the open end of the conduit beneath the floor within the vicinity of the socket.
Be warned that, if you did decide to take the conduit approach, then rodents seem particularly interested in cables where they emerge from holes (including out of open-ended conduit), so the conduit could actually increase the 'rodent risk' if you did as you suggest.

Kind Regards, John
 
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Old cables, early 70s. Old colours. Got a new reel of 2.5 so might as well put to good use.

Yes worried about the beasts, and potential 'replaceability'
With or without conduit, the meeces could still have a nibble. It would be nice to be able to replace a section of cable between sockets without getting the whole floor up again.

I understand the conduit may affect the rating of the cable/circuit. Currently on a 32a MCB

Changing it for a 25a might be sensible?
 
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Changing it for a 25a might be sensible?
2.5mm² in conduit has a rating of 23A which is adequate for a ring circuit with a 32A MCB.
If the conduit is in thermal insulation, that comes down to 18.5A

Whichever, larger cable would be preferable.
 
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Yes worried about the beasts, and potential 'replaceability' ... With or without conduit, the meeces could still have a nibble. It would be nice to be able to replace a section of cable between sockets without getting the whole floor up again.
Fair enough, but I'm not sure how the replaceability of cables between sockets (if above floor level) would be influenced by what you do beneath the floor. I just wanted to warn you that if cables emerge from open-ended conduit in accessible places, they would probably be particularly susceptible to rodent attack in such places.
I understand the conduit may affect the rating of the cable/circuit. Currently on a 32a MCB .... Changing it for a 25a might be sensible?
EFLI has given you the relevant figures. A ring final circuit frotected by a 32A MCB is allowed so long as the current-carrying capacity (CCC) of the cable (as installed) is at least 20A - so '2.5mm² just in conduit' (23A) would be OK without de-rating the MCB.

However, the corollary of the above is that a ring final circuit (the main advantage of which is that there is a dispensation for the cable to have a lower CCC than the rating of the MCB) is not allowed if the CCC of the cable is less than 20A. If you had 2.5mm² in conduit in insulation (18.5A), the regs would not allow that dispensation, so you'd be down to having to protect the circuit with a 16A MCB - both silly and making a nonsense of having a ring.

Kind Regards, John
 
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Old cables, early 70s. Old colours. Got a new reel of 2.5 so might as well put to good use.
That is not good use, it is a waste. There is no requirement, or point, in changing cables just because they are red//black.
 
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I have no bending facility and don't want to terminate the conduit into every socket box
Don't bother with conduit then - it will be very expensive, rather difficult to shove T&E through, and the ends will still need something fixing to them to prevent the cables being damaged.

If rodents are a concern, clip the cables to the underside of the joists and cover with metal capping
https://www.tlc-direct.co.uk/Products/SC2.html
 
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I have no bending facility
You could acquire it.

Or use preformed bends/elbows.


and don't want to terminate the conduit into every socket box 'door to door', but just have the open end of the conduit beneath the floor within the vicinity of the socket.
As above, all or nothing, really, or there's no point.
 
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If rodents are a concern, clip the cables to the underside of the joists and cover with metal capping
Still the same problem though of unprotected lengths emerging from under the capping?

If the cables aren't currently being chewed by rodents, I don't see why the insulation will make things worse.
 
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The only way to replace wiring without taking up floors is a complete round conduit system wired in singles.

Would PVC round conduit be adequate?

If a complete system was done in PVC conduit it would be easier and quicker to install, and would offer SOME protection.

If you do this, use EGA weld glue or similar on the joints, as it would be irksome if the conduit came apart when replacing wires.
 
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20mm plastic tube is what the electrician used when wiring my garage. As long as the ring is a true ring you'll be OK, don't try running 4 lots of 2.5mm phase & 2 lots of 1.5mm CPC through the upstands to the sockets though, it is a very tight fit. Either 2 tube runs to each socket or use 25mm tube (which in your circs will be a real pain).
Your best bet (while the floor is up) is find out how the beasties are getting in and block it up- you really don't want a dead mouse/rat under the floor, it'll stink the place out for weeks. Fine heavy mesh will maintain airflow and keep critters out- Google it, there's loads
 
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