Under floor heating over 3kw

[Strima]

Minimum cable CSA for other circuits is 1.5mm unless wired in flex. I’m not at home at the minute so can’t give the reg number.

I would get the builder and customer there at the same time to explain my concerns and solution then let them make a decision.

If signing this off you are taking responsibility for the circuit and the UFH mats, how do you know he hasn’t damaged them on installation? Wouldn’t be the first time someone has been blamed for damaged UFH.

Unless I knew the builder well I wouldn’t be signing it off.

 

[Midwest]

As an aside, hope the customer has deep pockets to afford the leccy bill.

 

[Simon47]

... he did say he cut a couple mats down ...

As Davesparks says, with some (many, most ?) systems, you cannot cut them down - and where you can, it may need special measures to maintain the integrity of the element.
Some "mats" are simply a wire system that's pre-laid out on a plastic mesh to make it easier to install. Some heater cables have multiple heating elements which can be cut in certain places. Others cannot be cut as the L&N wires are the elements, and are joined together at the far end - if you cut it then you need to re-join them and the resistance will be lower and the W/m higher than designed for.
So this alone should ring alarm bells. Make sure that you document everything that you were not involved in so they can't come back to you if there's any problems.

 

[DPG]

Maybe show the customer some of the comments on this thread.

 

[ferg]

Start off by walking away, slowly working up to a light jog culminating in a full blown sprint.

 

[westward10]

How come you are concerned with what the builder has done.

 

[HappyHippyDad]

How come you are concerned with what the builder has done.

Because he may not be as self assured as you are Westward. He probably has a working relationship with the builder and feels he has to tread lightly. Even though my builder is a friend there are still times when i think 'should I or should I not put my foot down on this point'. Having said that, this is one time I would definitely be putting my foot down.

 

[telectrix]

this is one time I would definitely be putting my foot down.

hopefully not too hard on the UFH mat.

 

[matthew stephenson]

1.5mm is the minimum for a power circuit. It's in the regs somehwere. 1.0mm is only acceptable for lighting circuits. Really should have it's own circuit also. Definately can't sign this off. What do you think the nic/napit inspector would say?

 

[Deleted account]

1.5mm is the minimum for a power circuit. It's in the regs somehwere. 1.0mm is only acceptable for lighting circuits. Really should have it's own circuit also. Definately can't sign this off. What do you think the nic/napit inspector would say?

What’s the definition of a power circuit?

surely all circuits are power circuits. I know I’m being pedantic, but I see nothing wrong with using 1 mm for a dedicated circuit that needs minimal power. Cheaper and better for environment.

i agree a spur from a socket circuit minimum is 1.5mm whether ring or radial as long as it is fused down as per regs and it’s what I do,

but in theory 1mm fused down spur from a ring or radial socket, I see nothing wrong with that.

 

[davesparks]

What’s the definition of a power circuit?

A circuit which is not a lighting circuit.

 

[Strima]

If you look at table 52.3 it also depends on the type and material used for the construction of the cable.

 

[lozarus]

Just an aside - I've only ever been involved with UFH once so am by no means expert, but I seem to remember the installation instructions for my example demanding IR tests to be done before the mats are fitted, once they're laid down and again after the floorcovering is installed to keep an eye on the condition of the mats throughout the installaton process. Certainly the one I used provided an area for these results to be noted and suggested it to be left by the CU (apologies can't remember the make). But with this in mind, i'd be concerned about an installation I hadn't been fully involved in

 

[Simon47]

Not just IR, resistance as well. Both should stay stable - you really need to detect faults before the floor goes down on top (especially tiles !)
IIRC, my mate's system came from Topps Tiles and the "one free repair" offer was conditional on having taken these measurements.