Max load on a 1mm T&E cable

[iep]

Had an electrician come in and install the wiring for an underfloor heating system (electric, 3kW). He has used a 1mm T&E cable to run from the fused outlet to the 'stat/control box for the heating and the cable is getting very warm while in use.

I'd never have thought a 1mm cable would be up to the job and most of the info I can find online would back this up.

Is there some circumstance under which 1mm is considered okay for such a high load?

Cheers,

iep

 

[EFLImpudence]

1mm² twin and earth is rated at 16A maximum if clipped to surface or buried in masonry.

 

[iep]

This has been run in tightly backed steel conduit. Gets quite warm when in use.

iep

 

[EFLImpudence]

13A in conduit - still ok - but less if there are other cables in it as well.

(Did you mean tightly packed?)

 

[iep]

Yes, sorry, tightly packed with other cables. Suspect that might be the problem. That said, is it actually okay for it to be warm during use?

iep

 

[EFLImpudence]

It depends what you call warm and what the other cables are.

If it is just warm - i.e. not cold - it may be alright but definitely should not be 'hot'.

 

[iep]

It's not 'hot' just quite warm. Other cables are the thermostat return from under the floor and the output of the thermostat to the underfloor element (a nice heavy flex).

The question is whether adding a 1.5mm or 2.5mm cable would make things better given that it would get even more packed inside the conduit?

Cheers,

iep

 

[EFLImpudence]

Well, strictly speaking, it does not seem to be entirely compliant.

Perhaps you should contact the electrician and voice your concerns.

 

[iep]

Yeah, I agree, just a load of hassle and in the meantime, a freezing cold house. Was hoping to be told it'd be okay but my gut feeling is that it needs sorted.

Pain in the arse is that I'd normally do this kind of job myself (and would have used 2.5mm) but thought I'd go the legit route and hire a spark this time.

Cheers,

iep

 

[PrenticeBoyofDerry]

What does the manufacturers instruction state. I have come across plenty of UFH MIs that state to use 1.5mm cable.

 

[JohnW2]

No one seems yet to have commented, at least not explicitly, on the fact that, unless it can be argued to be a "lighting circuit" (and, try as I may .... ), use of 1mm² cable is non-compliant with the regulations.

Kind Regards, John

 

[EFLImpudence]

D'oh, forgot about that one.

I suppose it is a power circuit?

 

[Lectrician]

No one seems yet to have commented, at least not explicitly, on the fact that, unless it can be argued to be a "lighting circuit" (and, try as I may .... ), use of 1mm² cable is non-compliant with the regulations.

Kind Regards, John

What do the regs actually say?

 

[JohnW2]

No one seems yet to have commented, at least not explicitly, on the fact that, unless it can be argued to be a "lighting circuit" (and, try as I may .... ), use of 1mm² cable is non-compliant with the regulations.

What do the regs actually say?

Simply that the minimum permissible CSAs for copper conductors (in sheathed or non--sheathed cables) are 0.5mm² for 'signalling and control circuits', 1mm² for 'lighting circuits' and 1.5mm² for 'power circuits' (Table 52.3 - referenced by reg 524.1).

Kind Regards, John

 

[securespark]

Then there's the regs around how much space you have to leave in a conduit to prevent this very problem from occurring.

I can't find any direct reference to spacing factor in the regs, but 522.8.1 would cover it.