FCU Wired to Ring Main?
 

Hello

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

Cheers

Richard

Andy Wade wrote:
wrote:

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?

Alarm bells loudly ring. What's the scope of the underfloor heating
installation and what sort of load are we talking about?

I read in some posts that permanently fixed heating devices
shouldn't
be wired directly to the ring main and if this is true [...]

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.

--
Andy

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

From what I remember and by looking at the wires coming out of the
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

Thanks for your repsonses.

Cheers

Richard

Actually I was wrong the 2 heaters are about 1KW each, what do other
common applicances I mention in my previous post
draw?

Thanks

richard

"Stefek Zaba" wrote in message
...
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

He was negligent, and bull****ting too.

The room size is 20m2 but the UFH area is probably about 15-16m2

From what I remember and by looking at the wires coming out of the
screed there are 2 heaters and I'm pretty sure they are 2KW each.

(but you go on to say you think (!) they're actually 1kW 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

Well, it falls pretty squarely into what I called the "DON'T EVEN THINK
ABOUT IT" region. Toaster: 1kW; washdosh - 1kW or 1.5kW (intermittent -
much less when just sloshing already-heated or cold rinse water around,
but up at that figure while heating water and during final 20 mins or so
of air drying); coffee mc - prolly 0.5-1 kW; hot tub - god knows, if
you're heating it electrically then far-too-much not to be on its own
dedicated circuit already (it'll be 3kW), if it's only a pump and heated
off your CH then just a couple of hundred W, maybe, maybe a bit more for
lights too; fridge/freezer - a few hundred W; kettle - 2kW when used.
(Whether they're fed down a spur or from sockets/FCUs directly on the
ring makes not a whit of difference to the load on the ring.)

The hot tub issue alone makes me most uncomfortable (you mention an FCU,
but please God tell us there's a 30mA RCD on that circuit too). Even
without that, you've a peak load of pushing 5kW in the rare cases where
most of these appliances are running - that's 20A. Put even the 2kW
lower guesstimate of your UFH on the same circuit and you've used up the
whole of the circuit capacity, even without worrying about whether most
of that load is at one end of the ring (which means the bulk of the
current is carried by the shorter side of the ring, so making that
shorter cable section run disproportionately hot). Then someone plugs a
vacuum cleaner (1.5kW+) into the ring too... overload city here we come.

You *really* need to get this lot properly sorted: a new separate
circuit with its own RCD/RCBO for that hot tub, and a separate circuit
for the UFH if it's only 2kW (if there's two segments each of 2kW,
you'll want either two separate circuits each in 2.5mmsq, or one in
4mmsq - probably). Running the whole lot off one ring creates the
classic conditions for repeated, sustained, cable-najjering overloads
which are above the cable rating but below the point at which the 32A
MCB on the ring will trip.

Don't go there. Get it sorted.

Oh, and what is the room being UFH'ed? If (shudder) a sauna, does your
installer know about providing additional earthing and the like? (Or
maybe his horse does - y'know, the one he digs his spurs into with a
wild yee-ha! as he rides off into the sunset...)


With your money. :-)

Stefek

On Sun, 09 Jan 2005 08:41:46 -0800, r.rain wrote:

Actually I was wrong the 2 heaters are about 1KW each, what do other
common applicances I mention in my previous post draw?

Thanks

richard

Listen to Stefek, get someone in WHO KNOWS what they are doing !!.

Dave

--
For what we are about to balls up may common sense prevent us doing it
again
in the future!!

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?

Owain

Thanks for your advice Stefek.

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!

Thanks for your contribution Dave.

Richard

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.

The problem is that it is explicitly forbidden and would fail the
inspection. Do it properly and run a new circuit for the UFH.

Christian.

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

Richard

On 10 Jan 2005 02:00:24 -0800, strung together
this:

Is Owain or Lurch around, I would like a second opinion please,

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.
--

SJW
Please reply to group or use 'usenet' in email subject

On Mon, 10 Jan 2005 10:30:37 -0000, "Christian McArdle"
strung together this:

The problem is that it is explicitly forbidden

By who, and how exactly?
--

SJW
Please reply to group or use 'usenet' in email subject

"Owain" wrote in message
...
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?

Owain


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?

Cheers

Richard

That was meant for Owain BTW post looks like its got out of order!

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.

"Lurch" wrote
| Is Owain or Lurch around, I would like a second opinion please,
| Recognition at last! ;-)

There was a Lurch on Scrapheap Challenge last night - was that not you?

Owain

Owain wrote:

[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.

Hmm, that sounds familiar...

--
Andy

On Mon, 10 Jan 2005 21:04:18 -0000, "Owain"
strung together this:

There was a Lurch on Scrapheap Challenge last night - was that not you?

I dont think so. If it was I've forgotten what I built.
--

SJW
Please reply to group or use 'usenet' in email subject

On looking at the post again you DIDN'T in fact state that, so my
profuse apologies. Having problems telling who said what must do
better!

Anyway thanks for all the great information you have provided me. In
this case I will put it on the ring main but only due to the fact of
the MAJOR hassle it would be to put it on a sep circuit, so dont think
I'm just ignoring your advice and not answer my future questions ;) I
have learn't a hell of a lot just from this thread.

I will however plan to do this for the future when we renovate the
upstairs. I really didn't need the extra stress of trying to sort
wiring out as well as all my other jobs I have on at the moment. I'm in
stress city at the moment, I dont think I'll ever buy an old house in
need of renovation again. Nearly done downstairs now though and looking
sweet............

Thanks again

Cheers

Richard

:)
Well as usual I would just like to thank everyone for all their
contributions, you have all been a great help. See response to Stefeks
last posting

Cheers!

Richard