Underfloor Heating electrics...pretty competent DIYer

[Buzzcut]

Hey all...

This place has been my saviour many a time but I've never actually had to ask a question myself before. I've just bought some underfloor heating and need to get it wired in.

The page for the electrics is here

http://www.dumpt.com/img/viewer.php?file=0y5bz1vxdj2uif7hw74c.jpg

It says that the heater can be run from an existing circuit so I was thinking of taking it off the existing 30A plug socket ring that runs to the main fusebox.

There's a 13A double socket right outside the bathroom so above that would be a very convenient place to have the thermostat and isolator.

On the back of the Thermostat it says 16A 3800W max load so my question is whether the 30A circuit can take it. It says on the picture that "the electrician will be able to determine whether or not the circuit can handle the load and if it is RCD protected" but I thought I'd ask first in here....there's no actual RCD in the consumer unit but a 30A wire fuse.

Any advice? I'm well capable of chasing out and installing everything I just need to know if it's safe to do so, I don't really want to pay for an electrian to come out and just say "yeah that's fine..."

Cheers...Buzz

 

[oharaf]

I don't really want to pay for an electrian to come out and just say "yeah that's fine..."

No electrician worth his salt and membership would come out and say this!!!

It will require a full inspection and test!!!

Cheers...Buzz

Where are you installing the under floor heating?

Personally, any heating circuit I would want on its own supply.

3800W @230V is 16.5A @240V is 15.8A right on the limit!!!!

 

[Buzzcut]

Thanks for the quick reply...

I think my "Yeah that's fine" was meant to be more, "yes, go ahead and install it, when it's done, I'll come back and test the install"

I'll be installing in the bathroom but the consumer box is right the other side of the flat and I can't see how I can get it on its own supply.

The Thermostat comes with the underfloor heating so isn't that 16A just the maximum the floor can pull...or maybe I'm missing the point.

 

[davelx]

ooh, PP, my turn :

Work in bathrooms is notifiable under Part P of the building regs and there are special requirements for underfloor heating in the wiring regs which may require an earthed mesh over the top of the elements, unless they are specifically stated to incorporate this in their structure.

So this work either needs to be carried out entirely by or under the supervision of a self-certifying electrician, or notified to your LABC with appropriate fees in advance - in which case you will need to agree with them how the inspection and testing are to be done.

 

[oharaf]

You had better speak to your sparky who is about to sign off 'someone elses' work, after all he is going to carry the responsibility for it.

Does your flat have floor boards?

Does your CU contain an RCD with a spare way?

Bonding and tails up to regs.?

 

[LiamPope]

Does your CU contain an RCD with a spare way?

...there's no actual RCD in the consumer unit but a 30A wire fuse.

Doubt it

Looks like it's time for a new CU since you now need RCD protection. You could run it off the existing circuit in theory (if it could be RCD protected) - how much load is on it already? Far far better to give it a new circuit.

Liam

 

[Buzzcut]

...as you can tell I've had no experience with this depths of electrics before!!

It's a basement flat with a concrete subfloor.

The CU is the old fuse version not with RCDs,

30A for the electirc shower
5A lighting
5A lighting
20A - ABSOLUTELY NO IDEA!!...with this pulled out everthing in the flat still works, heating, shower, lights, sockets etc. It's wired up but can't see where this goes
30A Plug sockets
30A Plug sockets

I'm guessing the heater could go on this 20A fuse...

"Bonding and Tails" is a new one on me. I think I do need to find a local sparky to pop in and take a look. The manual and the installers in the shop I bought it from mentioned nothing about building regs etc and said I could install it easily myself (apart from the electics)

 

[ericmark]

I suppose I could also call myself a "pretty competent DIYer" as I no longer work and as such I fitted under floor heating into my parents wet room.
1) I had to write to manufactures to find out if I needed earthed mesh or not I was lucky it did not need it.
2) I found there was very little difference in price of whole new consumer unit to fitting a RCD just for under floor heating and since I was declaring under Part P anyway it seemed the right way to do the job.
3) Although the thermostat was rated 16A the heating element was only around 700W so I used a FCU and 5A fuse local to thermostat.

The county council did want to check I was a "pretty competent DIYer" and I had to show copies of my C&G 2391 and 2381 as it was then. And I had to show them the test gear I intended to use. Luck my son has two sets of test instruments so he could leave one for me to use.

I had to inspect and test and take results to council. He was worried on his visit as to if they failed what would happen but I assured him I knew what I was doing and it would not fail.

It was passed and the completion cert was dually received.

Although Part P does allow the DIY person to do work it is really designed for the "pretty competent DIYer" like me with a degree in electrical and electronic engineering and C&G 2391 and 2382 as it is now who although trained as an electrician is not registered under the system.

Do remember "Competent person" means:- A person who possesses sufficient technical knowledge, relevant practical skills and experience for the nature of the electrical work undertaken and is able at all times to prevent danger and, where appropriate, injury to him/herself and others.

As such you should be able to both measure ELI and PSC and interpret the results. The meters I borrowed cost my son £750 and most DIY people even if they could borrow them could not use them safely.

I would guess the 20A fuse would have feed an immersion heater and you may find it goes via a switch in kitchen it was normal years ago to include a switch. In my house it has been used to power extra sockets.

I would never use an electric shower without RCD protection. Neither would I use underfloor heating without RCD protection. So to fit two extra units with RCD's in I would think would not be cost effective and I would change whole consumer unit. And with only 6 circuits I would use all RCBO's as much less likely to trip without cause.

 

[ban-all-sheds]

There's a 13A double socket right outside the bathroom so above that would be a very convenient place to have the thermostat and isolator.

I don't think that a thermostat not in the room where the heating is would be a good idea....

 

[Buzzcut]

ericmark - Thanks for that very useful post.

The heating is actually only rated 600W so 2.5A is way below the 16A I initally thought it was...a 5A local isolator would work I guess. I've also just called the manufacturer and the Electirc Mesh is not needed.

And you hit the nail on the head with the Immersion heater, that's the one switch in the airing cupboard I didn't try.. I'll call someone out to have a proper look, I've been putting off getting a new CU for about 6 years since I moved in anyway.

ban-all-sheds - There is a wire probe that goes from the thermostat to under the floor, it doesn't measure air temp. The manual says not to have it in the same room if it's a bathroom anyway.

 

[ban-all-sheds]

OK

 

[Steve]

ericmark - Thanks for that very useful post.

The heating is actually only rated 600W so 2.5A is way below the 16A I initally thought it was...a 5A local isolator would work I guess.

Why didnt you tell us this before?

This whole thread has contributions based on the controller being rated to 16 amps. The controller rating has nothing to do with anything. We need the load rating connected to it!

The sparks above should hang their heads for not spotting this.

 

[Buzzcut]

It's always the most pertinent information that unfamiliar people give last..

I always assumed that the heater would pull 3800W max if it needed to. It only occurred to me to look at the actual rating when i read eric's response.

I guess your question should've been "why did no one ask this idiot the actual rating of the heater!?"

It's been very helpful anyway..

 

[kai]

You need a 3amp fuse for the heating, as it can safely carry up to 720 watts at 240 volts....

 

[Taylortwocities]

If you read the WarmUp Installation Manual, you will find a table that states the current draw for each of the WarmUp heating mats.

The size of fuse will depend on the mat's rating or it could be multiple mats.

All of the info is in the WarmUp manual. It includes all of the info regarding connections, RCDs, etc. It also states that an earthed metallic grid is not required.

EDIT: Read the note on page 4 of the manual with reference to Building Regulations Part P.