T&E in conduit in screed?

[ToastyToes]

I need to run ten cables listed below about 6/7 meters from the fusebox. They will go into screed for around 1.5m of the run. The screed is total 55mm deep, unless i grind out some of the concrete below.

x5 - 1.5mm lighting circuits
x3 - 2.5mm radials to unswitched sockets for dishwasher, washing machine and tumble dryer
x2 - 2.5mm for the ring main

Could I bury 2 or 3 25mm flexipipes in the screed and run the cable in that but I was concerned about cable temperatures.

Suggestions and advice required.
Thanks.

 

[Taylortwocities]

Of course you can do this, providing you do your cable calcs re grouping and remembering free percentage rule in conduit, etc.

 

[Notch7]

I need to run ten cables listed below about 6/7 meters from the fusebox. They will go into screed for around 1.5m of the run. The screed is total 55mm deep, unless i grind out some of the concrete below.

x5 - 1.5mm lighting circuits
x3 - 2.5mm radials to unswitched sockets for dishwasher, washing machine and tumble dryer
x2 - 2.5mm for the ring main

Could I bury 2 or 3 25mm flexipipes in the screed and run the cable in that but I was concerned about cable temperatures.

Suggestions and advice required.
Thanks.

I think the floor is in the safe zone -Im sure the pros will be along to correct me!

your electrician will advise on calculating the derating of cables in trunking.

 

[ban-all-sheds]

Could I bury 2 or 3 25mm flexipipes in the screed and run the cable in that

Why not use proper screed trunking? If your electrician hasn't suggested that then I wonder how much he knows about his job.

 

[rsgaz]

Pulling T&E through flexible conduit is no fun at all. You ought to use singles in rigid conduit with swept bends.

 

[JohnW2]

I think the floor is in the safe zone -Im sure the pros will be along to correct me!

Perhaps surprisingly, 'safe zones' (which is somewhat of a misnomer!) apply only to walls - not to floors or ceilings. One is therefore essentially left with the general requirement that cables in floors should be installed in a manner which minimised the risk of mechanical damage.

As has been said, 'flexipipes' are probably not the ideal, for a number of reasons.

Kind Regards, John

 

[winston1]

I need to run ten cables listed below about 6/7 meters from the fusebox. They will go into screed for around 1.5m of the run. The screed is total 55mm deep, unless i grind out some of the concrete below.

x5 - 1.5mm lighting circuits
x3 - 2.5mm radials to unswitched sockets for dishwasher, washing machine and tumble dryer
x2 - 2.5mm for the ring main

Could I bury 2 or 3 25mm flexipipes in the screed and run the cable in that but I was concerned about cable temperatures.

Suggestions and advice required.
Thanks.

Using 1.0mm for the 5 lighting circuits would help. 1.5mm is oversize and unnecessary.

 

[ToastyToes]

Using 1.0mm for the 5 lighting circuits would help. 1.5mm is oversize and unnecessary.

Could you explain why that would help? Surely larger cable is better? I've used 1.5mm for the lighting around the whole house.

 

[Taylortwocities]

Could you explain why that would help?

1mm² takes up less conduit space than 1.5mm². Simples.
The OP is needing to House 5 Lighting circuits, for some reason.

 

[JohnW2]

The OP is needing to House 5 Lighting circuits, for some reason.

I also wondered. Then I wondered whether they really are '5 circuits' in the sense that you and I would mean - it is possible that there are 5 'feeds' (to different things/places) from less than 5 actual circuits.

Kind Regards, John

 

[Taylortwocities]

Yes. Five separately switched feeds to the island.
Spots, plinth lights, etc etc. But (I’ve never tried to get) five x 1.5mm² T&E cables down a bit of 25mm conduit?
Methinks it would need more than one.

 

[Notch7]

Perhaps surprisingly, 'safe zones' (which is somewhat of a misnomer!) apply only to walls - not to floors or ceilings. One is therefore essentially left with the general requirement that cables in floors should be installed in a manner which minimised the risk of mechanical damage.

As has been said, 'flexipipes' are probably not the ideal, for a number of reasons.

Kind Regards, John

Ah ok, so there arent specific restrictions in floor and ceiling.

I suppose 'safe zone' isnt a good description. Its really 'the place where one should know where not to drill.

Ive always wondered about the 50mm depth, I think it would be very easy to drill that deep

 

[JohnW2]

I suppose 'safe zone' isnt a good description. Its really 'the place where one should know where not to drill.

Indeed - and I suppose it depends who you are. I presume it is the electrician for whom it is a (hopefully) relatively 'safe' place to bury cables. However, for any tradesman or DIYer with a drill, hammer and nails, cold chisel or whatever in his hand, it would probably be better thought of as a 'danger zone'!

Kind Regards, John

 

[ban-all-sheds]

Ah ok, so there arent specific restrictions in floor and ceiling.

Depends what you mean by "specific".

There are requirements for cables in floors and ceilings relating to mechanical damage.

 

[ban-all-sheds]

Could you explain why that would help? Surely larger cable is better?

So would 2.5mm² or 4mm² be better stil?