Hi All
I was hoping someone could shed some light on a question about the setup of my underfloor heating.
I live in a 1970s block of flats with electric underfloor heating. There are 4 heating circuits in total with the original 1970s wylex consumer unit. 3 of the heating circuits are each protected by 16a wylex rewireable fuses.
The fourth circuit is a more powerful heating circuit which draws a maximum of 23.3amps (measured with clamp meter). This is protected by a 32a rewireable fuse.
As I understand it, the current carrying capacity of 2.5mm PVC twin and earth isn't high enough to have a 32a fuse on it. However my flat and the heating circuit in question is wired in the original 2.5mm MICC (Orange sheath. I measured the cores and it does seem to be metric 2.5mm) cable. I don't know exactly how the underfloor circuits are installed, but I would guess the MICC is laid between the structural concrete floor slab and a layer of screed.
I've been in a couple of the other flats in the same block with the original wiring setup, and they also have the same 32a rewireable fuse on this same heating circuit, so I am confident it is as-installed upon construction, and the construction quality of the block of flats is good (ie. not thrown-up modern construction).
My question is this - Is the current carrying capacity of 2.5mm MICC higher than 2.5mm PCV T+E and is it high enough to allow safe protection by a 32a breaker? I've also read the attached document about overload protection - see the last two pages - which comments a bit vaguely on the requirements where overload protection isn't strictly required. The logic as I understand it is that because this is a fixed underfloor heating system which cannot be extended, it will never draw more than it's design load of 23.3a (except I assume when in fault), so overload protection isn't required? Except I then lose track a bit as to what the author is saying in regards to the associated reuqirements for cable rating and protective device.
Anyway as you can see I'm a bit confused and looking for someone to shed some light for me. I'd be grateful for any advice as there's not much info out there on MICC that I can find.
Thanks all in advance.
I was hoping someone could shed some light on a question about the setup of my underfloor heating.
I live in a 1970s block of flats with electric underfloor heating. There are 4 heating circuits in total with the original 1970s wylex consumer unit. 3 of the heating circuits are each protected by 16a wylex rewireable fuses.
The fourth circuit is a more powerful heating circuit which draws a maximum of 23.3amps (measured with clamp meter). This is protected by a 32a rewireable fuse.
As I understand it, the current carrying capacity of 2.5mm PVC twin and earth isn't high enough to have a 32a fuse on it. However my flat and the heating circuit in question is wired in the original 2.5mm MICC (Orange sheath. I measured the cores and it does seem to be metric 2.5mm) cable. I don't know exactly how the underfloor circuits are installed, but I would guess the MICC is laid between the structural concrete floor slab and a layer of screed.
I've been in a couple of the other flats in the same block with the original wiring setup, and they also have the same 32a rewireable fuse on this same heating circuit, so I am confident it is as-installed upon construction, and the construction quality of the block of flats is good (ie. not thrown-up modern construction).
My question is this - Is the current carrying capacity of 2.5mm MICC higher than 2.5mm PCV T+E and is it high enough to allow safe protection by a 32a breaker? I've also read the attached document about overload protection - see the last two pages - which comments a bit vaguely on the requirements where overload protection isn't strictly required. The logic as I understand it is that because this is a fixed underfloor heating system which cannot be extended, it will never draw more than it's design load of 23.3a (except I assume when in fault), so overload protection isn't required? Except I then lose track a bit as to what the author is saying in regards to the associated reuqirements for cable rating and protective device.
Anyway as you can see I'm a bit confused and looking for someone to shed some light for me. I'd be grateful for any advice as there's not much info out there on MICC that I can find.
Thanks all in advance.
