I've had my underfloor heating installed but not wired in yet. I plan to wire it in where I have removed a double socket, so on the ring main. Do I just wire in a FCU to the old socket cables and then the thermostat from that? I read in some posts that permanently fixed heating devices shouldn't be wired directly to the ring main and if this is true what is the correct way to do this using my existing ring main cables, do I need to use a junction box and spur from this? not sure how this is different though. Help and explanantions appreciated. TIA
The basic principle you mention is right: fixed heating appliances ought to have their own dedicated circuit from the CU. The reason is that when they're on (autumn/winter/spring) they're drawing a fairly substantial proportion of the total design current for the ring. So if you draw the previously-anticipated full load from the ring at the other appliances, you'll be in overload territory. Contrary to what you may imagine, the fuse or MCB in the CU will *not* do all that good a job of protecting the ring wiring from a "small" sustained overload - a 32A MCB will pass a current of say 40A more or less indefinitely, but the wiring will at that load - especially if much of it occurs close to one end of the ring
- be getting hotter than it should, over time pushing its way through the insulation at any bends and so on. Not good.
That said, we'd need to know what else is on the ring and (most of all) how much power your UFH will draw. At one end of the scale, if it's 1kW or less to keep a smallish bathroom warm to the feet, and the ring is dedicated to other upstairs bedrooms where you don't run any heavy loads (one PC doesn't count as 'heavy', a bedroom with 8 servers starts to!), it would not be best practice to run it off the ring, but wouldn't be desperately dangerous until you get around to installing a separate feed. At the other extreme, if it's up around 3kW or more, and you're proposing to connect it into a ring which also supplies your kitchen (washing mc, dishwash, microwave, kettle, yada yada) - DON'T EVEN THINK ABOUT IT.
You should really have laid a new circuit back to the CU as part of installing - or getting installed - your electrickle UFH. (I'm assuming throughout that this is an all-electric UFH you're talking about. If all you mean is some electrical control for a UFH coming off your CH boiler, things is different - but you'd presumably talk about 'connecting my zone valve and stat' not 'wiring it in'!)
Alarm bells loudly ring. What's the scope of the underfloor heating installation and what sort of load are we talking about?
Quite right. Any comprehensive space heating installation needs its own dedicated circuit or circuits from the consumer unit or distribution board. Unless this is something very small and localised it's not at all appropriate to feed it from an existing ring circuit.
Underfloor heating comes under the 'special installation' provisions of Part P and requires a Building Notice or installation and sign-off by a member of a competent persons scheme, even if no new circuit is provided.
Interesting stuff, the installer said it would be fine but I didn't see him analyse what was already on the ring so not sure how he came to this conclusion
The room size is 20m2 but the UFH area is probably about 15-16m2
screed there are 2 heaters and I'm pretty sure they are 2KW each.
On the existing ring which serves the dining room and the kitchen are the following:
Toaster, Dishwasher (spur), Coffee machine, hot tub (connected from a FCU which was spurred from the ring) and a fridge freezer (Spur) kettle is also there but very rarely used. The hob and the oven are on their own circuit of course
Richard wrote | Interesting stuff, the installer said it would be fine but I didn't | see him analyse what was already on the ring so not sure how | he came to this conclusion
I'm not sure how he came to any conclusion either. If he's being paid to install it then he should *install* it, not leave half the job undone. If he's not Part P certified then he must subcontract to someone who is. If he hasn't connected it, how do you know what he's installed actually works?
OK so in summary, I have done some further checking on devices to see what the draw will be
Hot Tub = 1.5KW Thermostat controlled and well insualted Toaster = 950W Rarley on Coffee = 1.2KW Rarley on Kettle = 2KW Rarely on UFH (Kitchen) = 2KW F/Freezer = 300W
So from my math when all these devices are on (They never will be) the total draw is 7.95 KW = 31.8 AMPS
So taking this figure and taking some advice I was given from this forum regarding wiring a cooker and a hob together on the same circuit I should be ok allowing for diversity. Just like to add here that Stefek you stated you wouldn't do this and that I should wire the hob onto a seperate circuit. I'm not stating here that you were wrong simply that some people tend to me more cautious than others, which when dealing with electicity is probably a wise thing to do.
Basically in this previous post it was stated that because my cooker and hob would never be on at the same time, meaning all elements, then a 9KW draw would be ok. I actually did put all elements on and the MCB didn't even trip. I didn't however leave these on for an extended period of time though.
In addition to this, if it was an easier job than it will be to wire these seperate circuits in as you suggest then I would do it without question. I have floorboards upstairs and the previous occupiers have built units over where the consumer unit is so this will be a hellish job and if I can get away without wiring in seperate circuits then I would like to.
Is Owain or Lurch around, I would like a second opinion please, they stated the oven and hob could go on the same circuit which turned out to be correct. However they did talk about cable lengths too so maybe this will come into play in my scenario.
BTW the hot tub is protected by a 30MA RCD and the company who installed it are basically the main players in the hot tub market and are not cowboys, also my UFH guy is not a cowboy either he also works for a very reputable company. It makes me laugh that people automatically assume everybody is a cowboy, now ask me about my kitchen fitter, he was a cowboy!
OK now we are getting there. Which part is explicitly forbidden, running the UFH from the ring main or the amount of load? If the latter then my cooker and hob together on one circuit (9KW) would fail if the work was done after Part P was introduced and I had to get it inspected. If you are saying the former then I will have some serious words with the installer as I would not of had UFH if I needed a seperate circuit, the only reason I got it was because we needed to get the floor levelled anyway prior to tiling so I thought what the hell. To re-iterate it will be a complete pain in the butt to run a seperate circuit and will involve dismantling a huge cupboard to some degree, that said looking likely I may need to do this now! SWMBO will not be happy its in her dressing room.
Sorry to ask all these questions, just want to get everything straight. Cheers Christian
On 10 Jan 2005 02:00:24 -0800, snipped-for-privacy@btinternet.com strung together this:
Recognition at last! ;-)
Right then, you could add another 2kW to the ring and it would be fine as the chances of having everything on for long periods of time simultaneously is near enough nil.
Just a quick add up and my kitchen ring has well over 10kW of potential load on it and I've never had a problem.
I would prefer it if the UFH were on a seperate radial but you shouldn't see any problems with the UFH on the ring. Depends on what's involved in running new cables in. If it does turn out that the UFH is causing trouble, move it over onto a radial later.
Funny that, but that's what I first thought. If he was paid to install it, then why leave the main connection for the householder to do by themselves? Unless he was a floor layer with no electrical experience, or an electrician with no Part P self certification. Weird that.
He is coming back after tiling has completed, I was currious and wanted to make sure what he's doing is correct and I will probably do it myself anyways to make sure its mounted all neat inside a kitchen cupboard. I have monitor boxes on at the moment which are monitoring the integrity of the UFH element just in case I drop a tile on the screed and break something. As for Part P I couldn't really give a hoot about it, as far as I'm concerned the work was done before the regs came in, my house, my problem if it goes South and I will continue to do electrical work. I already paid a BCO guy to come and do nothing when I knocked a wall down and erected a steel structure for an opening, money for old rope, another tax me thinks. As for the UFH company then they obviously need to make sure they are covered in some way but I didn't ask, they may well be.
So did you read the complete thread, interested to hear your opinion on what you would do regarding seperate circuit or not?
Richard wrote | So did you read the complete thread, interested to hear your opinion | on what you would do regarding seperate circuit or not? | That was meant for Owain BTW post looks like its got out of order!
I wouldn't have put electric underfloor heating in in the first place matey :-)
If it's *only* 2kW and the other loading on the ring is light and it's a right hassle to put in a separate circuit then I would probably spur it off the ring.[1] But then I wouldn't be doing it as a professional installer with a commensurate duty of care towards a customer.
Owain
[1] I have done worse things but my excuse is that I was only 13 and not given enough pocket money for proper materials to rewire the bedroom without my parents knowing.
So it'd be right on the limit of its design capacity, and when someone else plugs in a vac, or you put a dishwasher into the kitchen, or acquire a microwave, etc., you'll be overloading the kitchen ring.
It's because a ring is designed to be 'flexible' in meeting varying power demands that it's discouraged to connect fixed-load appliances to it. If you want to hear words from an Authoritative Book, how about this from Paul Cook (who heads the IEE technical committee which writes The Regs, AIUI) in 'Commentary on the IEE Wiring Regulations': 'In a domestic premise, it is preferable if water heaters and permanently connected heating appliances that are part of a comprehensive space heating installation are not supplied from the ring circuit supplying kitchen appliances and the distribution of the kitchen load needs consideration'. (section 6.2.2, 'Ring circuits', referencing Reg 433-02-04). So this guy's commentary doesn't say 'never', but rather 'discouraged'. Other commentaries - Steward & Stubbs, from memory - are fiercer and just say 'don't', AFAIR.
I'd be surprised to find I'd said that ;-) A year or more ago Lurch and I had a robust difference of views over hob-n-oven connection, in which I was firmly on the 'permissive' side with Lurch on the 'gert big cables throughout' side. Cookers are the classic example of allowing a lot of diversity - they're rarely used at their 'full' loads and even then the various elements switch in and out of circuit quite frequently under thermostatic control; and there's particular dispensation in the Regs to treat an oven and hob in a single domestic kitchen as a single cooking appliance (which sanctions counting the load from that combination as quite a lot lower than if you treated them separately). Your kitchen ring - which already has one relatively heavy fixed load on it, the hot tub - is designed to support 'typical' kitchen usage; by adding another fixed long-term load - the UFH - you're taking it a long way from its design assumptions. *You* may use fewer electrickle appliances than typical in the kitchen; any future user (and anyone they get in to do an electrical inspection) *will* barf on seeing a UFH *and* a hot tub sharing the kitchen ring, which current Regs-compliance thinking already points out as 'the ring most likely to need extra thought'.
Your consumption figures show you're not in immediate danger of overload on the proposed single ring. But any electrician doing an inspection that they're answerable for will not want to commit themselves to saying that, and will label the UFH-on-the-ring as a "2" - "requires improvement" - if feeling generous, or a "1" - "requires urgent attention" - if not. In practice it's your decision whether to go through the hassle of running a separate feed for the UFH now, or later if your kitchen usage patterns change or you come to sell up.
Again, I'd be surprised if I'd said you needed separate circs for an oven and hob - do you have a Google reference or a Message-ID:? The ones I see on a quick look don't mention "put them on separate circs"...
Glad to hear the hot tub has an RCD. As to spurs and reputable companies
- that's what second (third, and fourth) opinions are for, innit. And here on Usenet they're ten a penny ;-)
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