Wiring in a 60w heater permanently from ring

[dabaldie]

Ok, someone correct me if i'm wrong but i need to fit a small heater (60w) (yes sixty) inside a built in cupboard to air air circulation.

This is the way i assume you would do it:

Disconnect the supply.
Remove one cable from a nearby double socket.
Reconnect this cable to a 20A Junction box.
A new length of 2.5mm cable from the junction box back to the original socket.
Now connect the Live, Neutral and Earth terminals in the JB to (any cable will do, say 1mm^2 (as it is only 60w (but better to use 2.5?)) to a Switched FCU (mounted at low level outside the cupboard. Then connect this in turn to the tubular heater. What fuse? 3A or 1A (0.26 of an amp drawn)

This is how i picture it. Is this correct?... is there anyway of doing it without using a junction box, (ie switch that has a spur connection which wont break the ring). Is the way i have descriibed the easiest and safest way. I dont want or need to run a completely seperate circuit/spur from the CU just for a 60w outlet.
As for Part P (just a mention so dont shoot me down in flames), its technically just adding a spur in a bedroom so therefore is not notifiable.

Please point out any mistakes i have made. As ideally i need to do this this w/e as the new cupboards are being fitted next week and i need to lift floorbaords.

 

[ban-all-sheds]

Disconnect the supply.

And verify that it is disconnected, and ensure that nobody will turn it back on whilst you are working on it.

Remove one cable from a nearby double socket.
Reconnect this cable to a 20A Junction box.
A new length of 2.5mm cable from the junction box back to the original socket.

1) 30A JB
2) Why not put the FCU properly on the socket circuit? i.e. connect the cable you removed to the supply terminals of the FCU, along with a new length continuing on to the socket?

Now connect the Live, Neutral and Earth terminals in the JB to (any cable will do, say 1mm^2 (as it is only 60w (but better to use 2.5?))

2.5mm² much better.

to a Switched FCU (mounted at low level outside the cupboard.

Or inside.

Then connect this in turn to the tubular heater. What fuse? 3A or 1A (0.26 of an amp drawn)

3A will be fine, and a lot easier to find than 1A.

Also, if the heater doesn't have one, I'd advise fitting a thermostat in the circuit to avoid any risk of the cupboard getting too hot.

What surface temperature does the heater get to? Have you considered using something like this?:

 

[fr1day]

New to the site and been flicking through old posts with personal queries and out of interest.

I know this is an old one now but I've just seen it and wondered if anyone could answer:

ban-all-sheds> why 2.5mm2? 1mm2 is rated up to 5A for a BS1361 or 3036 protective device, or 6A for BS 88. You recommend a 3A fuse in the FCU so surely 1mm2 cable is more than adequate?

Also I've been thinking a while now about 20A junction boxes in ring mains circuits. You can cut down from 6mm2 cable from radial main to 2.5mm2 cable in a ring main and yet supply the same 30A current based on the fact that the current can circulate two ways round the ring. (The combined csa of the 2.5mm2 cables both ways gives 5mm2, which is (nearly) equal to 6mm2 of the radial). To follow on then, surely you only expect each half of the ring to only see half of the current (15A) at any one time. So shouldn't a 20A JB in a ring main be OK? ......

 

[Qedelec]

Man fr1day, It is always better to continue a circuit in the same size cable as the rest of the circuit. That way its future proofed, and its easier to identify which circuit it belongs to.

 

[ban-all-sheds]

Re the JB - the current doesn't always balance out 50/50 - it will only do that if all of the load is at the mid point.

If, say, you had 2 twin sockets next to each other, 10% of the way round the ring, each supplying a total of 15A, then 27A would be flowing in one leg of the ring and 3A in the other.

And depending on how the cable is installed, you could have problems. This is why the regulation that actually permits 30/32A ring finals wired in 2.5mm² in the first place require that the capacity of the cable not be less than 20A and the current in any part of the ring to not exceed 20A for any protracted period.

So given that, I guess a 20A JB would technically be OK, but I can't see the point of not using a 30A one....

 

[fr1day]

Thanks for the replies and explanations. Very helpful.

b-a-s>still one for thought then! Though I guess 'better safe than sorry' is always going to be the best route with using a 30A JB - overrated components can never hurt so long as the protective device for the circuit is correctly selected, and you get more room in the terminals in the 30A box.

I never like to just do for the sake of doing - it can be worth the extra question sometimes.