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Topic Title: Outdoor Heater Install
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Created On: 15 May 2014 05:24 PM
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 15 May 2014 05:24 PM
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Grayston

Posts: 25
Joined: 12 December 2012

Guys,
Been asked to install a 4.5kw outdoor wall mounted heater.
Now as the heater will be knocking on the door of 20A full on I was going to put a new feed in from the board. Its a new board so has RCD's already.
Was going to run 4mm to it via plastic conduit, but as you can radial 2.5mm at 20A, what do you think?
I'm leaning to 4mm, but will take offers. run length is approx 10m.
 15 May 2014 05:37 PM
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mapj1

Posts: 9577
Joined: 22 July 2004

Depends what you are going to run the cable through and alongside - yes 2.5mm is good for 27 amps when well ventilated, but this shrinks back to more like 22 if the conduit is in a wall, and less again when grouped with other wiring.
There are not many situations when 2.5mm is not enough. Actually if it was SWA or twin and earth clipped direct or on overhead catenary wire you would be just about OK with 1.5mm for this load and distance !
You could do worse than have a play with the calculator here as a starting point.

An online calc for voltage drop etc.

regards Mike

-------------------------
regards Mike
 15 May 2014 05:54 PM
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Grayston

Posts: 25
Joined: 12 December 2012

Cheers Mike, will have a look at that, was going to run it on an outside wall in conduit. must admit a do tend to air on the over the top side, but did think about the 2.5mm option.
cheers for the advice, much appreciated as always with this forum, best one on the net!
G
 15 May 2014 07:53 PM
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mikejumper

Posts: 2454
Joined: 14 December 2006

Originally posted by: Grayston
I'm leaning to 4mm, but will take offers. run length is approx 10m.

I find it easier with borderline situations like this to err on the cautious side and be done with it.
Fit it and forget it.
 16 May 2014 09:42 AM
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Grayston

Posts: 25
Joined: 12 December 2012

that calculator is interesting, never would have thought 1.5mm would be ok though.
I guess in theory you could spur off the ring final. dont think I would, I prefer a dedicated supply.
 16 May 2014 09:55 AM
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mapj1

Posts: 9577
Joined: 22 July 2004

Yes, fun isn't it. I've mis-used it once or twice to sanity check other people's designs that look a bit wrong when I've been away from the big book of tables.
Once can save a bob or two by not fitting a cable that's too oversize,but being right on the knuckle means folk ring up and tell you the cable feels warm and they dont like it.

I would not put 4.5kW on a ring either, its rather more than one should really take off at one point and doesn't leave very much left over for all the things that folk actually want to plug in. Actually I dont really like wto see water heaters/ immersion heaters on spurs from the ring either but I realise it doesnt usually give a problem.

However a decicated 20A radial from the board in 2.5mm should be fine if its not bundled up with a load of other wiring thats all sweating merrily.
M

-------------------------
regards Mike
 16 May 2014 02:02 PM
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Grayston

Posts: 25
Joined: 12 December 2012

Thinking the same thing there, just got to supply it from a Crabtree Starbreaker board, which has no spaces left on the RCD side! 2 spaces on the non rcd side so was going to fit a RCBO. its the only way without replacing the board. i'm sure the guy would love me to install a new board just to supply a garden heater!
i could drop singles in a conduit to get a bit more out of the 2.5mm, looks like 24A using the tables.
 16 May 2014 02:17 PM
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OMS

Posts: 22400
Joined: 23 March 2004

Why the focus on RCD or RCBO protection ?

It's not a socket, it's not a cable buried in the structure less than 50mm from the surface, it's not in a special location such as a bathroom.

That might save you more than debating 1.5mm2, 2.5mm2 or 4.0mm2 for a 4.5kW heater load.



Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
 16 May 2014 03:06 PM
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Grayston

Posts: 25
Joined: 12 December 2012

its an outdoor heater, I assumed it needed one due to being outside? although all parts bar the switch will be above head height.
 16 May 2014 04:03 PM
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OMS

Posts: 22400
Joined: 23 March 2004

Originally posted by: Grayston

its an outdoor heater, I assumed it needed one due to being outside? although all parts bar the switch will be above head height.


What are you basing that assumption on, as the designer - no one is likley to be handling or gripping a heater in the smoking shelter are they - nor is it mobile.

Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
 16 May 2014 04:13 PM
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mapj1

Posts: 9577
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Actually, I'm not sure that I'd recomend an outdoor anything that could get wet to share an RCD with anything too critical, and especially if its the only RCD for the whole place, either RCBO or just MCB is probably the better way to go.

Is it a location where damage to your cable is likely? actually in OMS's analogy of the smoking room, I'd be umming, perhaps if it was a public building where inebriated folk doing something odd near the heater is likely, then actually there is some merit in the additional protection.
regards
Mike.

-------------------------
regards Mike
 16 May 2014 04:44 PM
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OMS

Posts: 22400
Joined: 23 March 2004

It's in conduit isn't it ?

Most smokers, (p*ss*d or not) haven't got the lungs for a concerted attack on a cable to the only thing that keeps them warm

Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
 16 May 2014 04:57 PM
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Parsley

Posts: 1353
Joined: 04 November 2004

If you really want to over engineer it why not make it TT as well

Regards
 16 May 2014 05:43 PM
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OMS

Posts: 22400
Joined: 23 March 2004

Originally posted by: Parsley

If you really want to over engineer it why not make it TT as well

Regards


Or buy a gas patio heater

OMS

-------------------------
Let the wind blow you, across a big floor.
 16 May 2014 05:51 PM
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mapj1

Posts: 9577
Joined: 22 July 2004

I was suddenly seing visions of people spilling half a pint into the heater or a pile of cigarette butts accumulating around the wire and catching light.
Maybe its just the sort of places I frequent.

I can argue it away again, its not a strong feeling about the RCDs.

M.

I manged to give up smoking before it became a seriously exiled activity, but I do have some sympathy for the poor chaps who still sacrifice themselves so valiently to keep the pension fund in balance . Now in addition to lung cancer &c. one has to add the pneumonia risk to their burden.

-------------------------
regards Mike
 16 May 2014 08:04 PM
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OMS

Posts: 22400
Joined: 23 March 2004

I'm still a resolute afficianado of the evil weed - never mind pneumonia from standing out in the cold and wet, you're more likley to get mown down by the lunatics driving by the front door when you step out for a gasper whilst under the 'fluence of a few pints of good ale

Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
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