Breaking ring main

[xnetdude]

Lectrician - sorry missed your question amongst the red mist.

It's simply a matter of where the cable needed to be run. It has to squeeze behind and around a fair bit of boxing and a 1.5 t/e just about fits around the corners. Nothing suspect as you mention, just a tight squeeze.

I think the 5A FCU between the a ring and the 1.5mm cable is the way forward for us.

As a related? question - does anyone have an opinion if the lighting circuit could be used instead as the heating mat is only 150w. That way a cable can be run down the wall void with the appropriate 5A FCU installed in the attic?

 

[Bluehair]

I would not have any problems with running the UFH from the lighting circuit.

The UFH will need RCD protection - either at the CU or via a RCD fused spur

 

[bernardgreen]

Feeding from the lighting circuit is an option.

But you need to consider several things. Can the lighting circuit take the extra load. Add up all the wattages of lamps on that circuit then add 50% If that is less than 1000 watts then adding the heating mat will probably not overload the lighting.

The 50% is to allow for the extra load that a lamp takes when switching on.

The FCU should be fused at 3 amps. That may mean a fault in the mat will not take out the MCB and the lights.
The FCU should be double pole. That will ensure a fault in the mat can be fully isolated ( live and neutral ) allowing the lighting circuit to continue to function.

Under floor heating should be supplied via an RCD ( earth leakage breaker ) to minimise the risk of electric shock should a fault or damage or water ingress occur.

If running on the lights circuit you will lose your lights until the double pole FCU can be found ( in the dark ) and switched OFF.

 

[Taylortwocities]

And one last thing to consider...

The work of installing underfloor electric heating, in a special location is (still) notifiable under Building Regulations Part P.

So you will need to contact your LABC BEFORE you start work, or use a registered electrician.

 

[xnetdude]

Yep understood about Part P etc.

Thank you very much guys for the help - I have already worked out the load on the lighting and it will be fine - phew - much easier route!

Thanks again for the comments.

 

[ban-all-sheds]

Yep understood about Part P etc.

So when you request approval to carry out the work, what will you say will be the way you'll ensure that you comply with Part P?

 

[flameport]

It's simply a matter of where the cable needed to be run. It has to squeeze behind and around a fair bit of boxing and a 1.5 t/e just about fits around the corners.

That suggests 1.5mm won't be suitable either. Cables have a minimum bending radius to avoid damage, and if 1.5mm just fits around these corners and 2.5mm does not, the cables will probably be damaged when installing them.

As a related? question - does anyone have an opinion if the lighting circuit could be used instead as the heating mat is only 150w.

Electrically it can be done.
It will be totally pointless, as 150W of underfloor heating will do nothing other than waste energy.

 

[AdamCH]

is this 150w total or 150w per m2?