2.5mm MICC on 32A breaker

westward10 · Monday at 10:12 AM

It there anything written on the black sleeving fitted over the wires?

johnnyuk · Monday at 10:26 AM

westward10 said:
It there anything written on the black sleeving fitted over the wires?

Without taking the underfloor heating CU off the wall I can't be sure, but the other MICC cabling in the flat has labels that appear to read "734-02 A.P5" and 734-02 A.P4" but my plasterers tried hard to get as much plaster on the wiring as possible so a little difficult to read.

The UFH is definitely also MICC, just not sure what grade as can't get to it easily.

westward10 · Monday at 10:35 AM

Is the MI at the consumer unit to see it there?
The black sleeving normally has writing on it although there is no guarantee they used the correct sleeving.

johnnyuk · Monday at 10:48 AM

westward10 said:
Is the MI at the consumer unit to see it there?
The black sleeving normally has writing on it although there is no guarantee they used the correct sleeving.

you can only see the tops of the glands in the depths of the consumer unit. Like I say if I took it off I might see a little more, but there is black sleeving on the cores but only as big as the 2.5mm cores so not big enough to have writing on. Like I say it's at least the same diameter (8.1mm) cable as the cable used for the main ring circuit in the flat.

The black sleeving had the above sticky labels attached to them - these were on nearly every outlet in the house so I have to think they were there for a reason (to identify the cable). I sent the codes I mentioned to pyrotenax last week but they didn't reply.

westward10 · Monday at 11:01 AM

1970s you would have to assume they are metric but that is no guarantee as people were using up imperial cable through the 70s after everything became metric. 735 doesn't really mean much to me as it is not an imperial size and if it was it would be large, I have attached an imperial to metric conversion table. If you could see the sealing pot it would be stamped.

Screenshot_20250217_105906_Adobe Acrobat.jpg

johnnyuk · Monday at 11:12 AM

westward10 said:
1970s you would have to assume they are metric but that is no guarantee as people were using up imperial cable through the 70s after everything became metric. 735 doesn't really mean much to me as it is not an imperial size and if it was it would be large, I have attached an imperial to metric conversion table. If you could see the sealing pot it would be stamped.View attachment 119724

Thanks. I measured the copper cores pretty carefully with an electronic vernier caliper and I'm satisfied the cores are 2.5mm2. I also measured the outer diameter of the cable and it came in at 8.1mm which is the right size for a metric 2.5mm2 500v cable, but even if I got that wrong, the nearest imperial version based on your table is the 324, which has the same ratings anyway - 33a for covered cable.

Does the fact it's under a screed mean it should be derated or is @Tom256 's hunch correct that MICC doesn't need to be derated?