ring main size

[wattsup]

In relation to an earlier thread.
I need to quote for tree hugger type house, super duper insulation in cavities (some type of expanded foam + other stuff)
anyhow the spec is quite clear, allowance and cable size must be allowed for in your quotation (insinuating cable size is not standard) ..blah blah blah, without actually saying what size,
For the cooker, shower etc its quite straight forward when knowing the exact load on a said circuit...for instance I calculate the 2.5kw water heater needs to be wired in 6mm...
But what size a ring main, where the load is unknown, if on full load of 32amp I get a stupid size of 10mm, allowing for half i need 6mm, yet I know its very unlikely the load will exceed 10 amps, even in kitchen no more than 20 amps, split on one radial and one ring main...so what size cable for ring mains?

 

[Spudnik]

Dont see any reason why you cant install a 4mm RFC, rated at 32Amp

 

[old dog]

Dont see any reason why you cant install a 4mm RFC, rated at 32Amp

i have never seen a ring over 4mm remember it is a ring go with jason on this
4mm

 

[gunner]

in the 2392-10 syllabus it quotes that 4mm is becomming more and more the norm for ring circuits where cables have to pass through infills etc etc

 

[Jimmyb]

As long as the wire has not been derated below 20A in any part of the ring then a 2.5mm is ok but i would make it a 4mm if the budget allowed

T&E cable above a plasterboard ceiling covered by thermal insulation NOT exceeding 100mm thick is 21A but if it exceeds 100mm think then its only 17A so you would have to use a 4mm ring if that was the case

T&E cable in a stud wall with thermal insulation with the cable touching the inner surface of the wall (clipped to wood joist, somewhere to disperse heat) is 21A so fine but if not touching the inner surface its only 13.5A and even 4mm isnt any good as this is only 17.5A but
A single T&E cable enclosed in conduit in an insulated wall is rated at 20A so this would over come the cable drops ect but with a cost.

 

[steamboatwilly]

2.5mm RFC via a 20A MCB? This de-rates the RFC to compensate for the insulation?

 

[Jimmyb]

2.5mm RFC via a 20A MCB? This de-rates the RFC to compensate for the insulation?

no no no, still 32a mcb it just as long the cable can take 20a per leg

 

[drywax]

I remember seeing grand designs were they wired a straw house, I think they used that fire cable stuff thats impossible to bend but I have no idea what its called or what dimensions........

I hope that was no help at all

 

[Sintra]

I remember seeing grand designs were they wired a straw house, I think they used that fire cable stuff thats impossible to bend but I have no idea what its called or what dimensions........

I hope that was no help at all

Is it MICC you mean?

If it is, that would be a bit extreme for wiring a RFC in a domestic installation regardless of insulation and derating factors.