Non-copper wire in ring main?

[Dave Plowman]

But stranded copper 7/0.29 does bend easier than 2.5 solid - especially if rubber.

[Jerry Built]

Hi Ewan,

I shall be very surprised indeed if this is anything but tinned copper PVC covered cable. I have seen a lot of this around, and in general there's nothing wrong with it, exept that it does not conform to current standards (being multi-stranded rather than single). If the insulation is OK (not nibbled by rats etc) it should be perfectly OK for some considerable time to come.

J. --

[R W]

What's the story behind the switch from 15A to 13A sockets? Surely 15A would be more useful....?

[Dave Liquorice]

15A was radial and generally only one socket per room. Count all the sockets in a modern house then think about the size of the CU for that number of MCBs...

[Andrew Gabriel]

The design aim was for 3kW, which is where the 13A comes from. I guess there probably weren't any portable appliances over 3kW in use. Kettles of that era tended to be lower power than today's ones. I have come across a 3kW portable convector heater which could date back to that era, which is rather ironic as you'd be hard pressed to find one over 2kW nowadays.

[Jerry.]

Yes, but why switch from a 15 amp rated socket to one with a plug / fuse rating of 13 amps, in other words, why a maximum of a 13 amp fuse and not a maximum of 15 amp ?

[The Natural Philosopher]

I am not sure. The technology was sold to and continues to be used in south africa.

The square pin is allegedly easier to make a decent high current self wiping contact with than the old round pins, and I suspect what happened was somethig like this.

(i) let's move to ring mains cos we need a LOT of sockets these days, and we can't radial wire them all, and ringing them is a bit safer and relaxes cable constraints.

(ii) let's go to a new and better type of plug.

(iii) now each appliance has its own plug, rather than one socket per room (or floor?), how much do we realistically need to rate a single point at...3KW sounds nice. Oh. Thats 13A then? Right. 13A it is...

(iv) Mmm. What will the cable stand. Ok, about 30A seems right for the sort of cable that isn't TOO heavy. Lets standardise on 30A or 32A fuses then.

(v) what about lights? Oh sod it. do them on spurs cos they are always a nightmare with cables flkying everywhere, and you seldomn need a lot of current for em. say fused at 6A - that is 12 x100w bulbs,. Thats plenty for a house.

(vi) What about all these other plugs and sockets? Oh sell em to someone who wants em. Africans will do.

(viii) I need to set up sockets for msall lamps on lighting circuits...oh well use teh 5A old style plugs if you must. At least people won't be able to plug cookers into em. and they shold take 6A before the MCB trips.

[Dave Plowman]

'Twas my understanding that it's still possible to get stranded 2.5mm singles for conduit use. And if multi-stranded cable was a no-no why is

6mm TW&E etc stranded?

[The Natural Philosopher]

3kw convector were common in the 60's as were 3kw electric fires.

My ma's house was originally wired with 15A stuff (1953), then it was changed to 13A stuff - still on spurs - fairly quickly, and a few bodged extra sockets added. A seperate fuse box for the electric cooker was added when the gas one was binned.

The main wiring is still rubber coated plated copper stranded in steel conduit, and it has never shorted, or blown a fuse or anything.

The addons were done in the 60's using solid core stuff. Some by me.

None of it meets modern regulatons, but it all still works, and the earths are good. No doubt when teh house is eventually sold in teh next ten years estimnated, it will get a total reinsulate, rewire, new bathrooms, extension etc etc. But it still soliders on in remarkably good structural condition.

[Christian McArdle]

Both mine and my mother's fan heaters are 3kW. They're pretty widely available. However, the cheapest in the range will be a 2kW, so they're probably more common to find, as most people are cheapskates.

As for convectors, a quick browse of argos shows five 3kW, one 2.5kW and four 2kW models available.

Christian.

[Dave Plowman]

There's really no point in a 2kW fan heater, given that all have thermostats.

[Christian McArdle]

I can think of two.

Firstly, the output temperature is lower. It is very easy to melt nearby plastic things accidentally with a 3kW.

Secondly, after the room is up to temperature, I tend to knock the power rating down to reduce cycling. I prefer the constant noise to one that goes on and off every five minutes. If half the power of the device is too high, then this will be less effective as it will continue to cycle rapidly.

Christian.

[Andrew Gabriel]

OK. It was probably well over 10 years ago when I last looked, and my recollection was that 2kW seemed to be the max available then.

Funny you should say that. One weekend I ended up working in an unheated office (warehouse sized open plan one). I was given a fan heater. On the 2kW setting, I felt nothing, but on the 1kW setting, it sent me a nice breeze of warm air. On further investigation, I realised that at 2kW, the exhaust air was hotter and didn't make it more than about 2 feet from the fan heater before just going vertically up missing me, whereas at 1kW, the air continued to move perhaps 4 feet horizontally before changing direction, so it caught me.

[Bob Mannix]

Err, I think that last point is one that supports a 3kW fan heater! You can only get up to temperature quickly and then turn the heat down with a 3kW heater (or it's better at it). You can run a 3kW fan heater at 2kW but not the other way round! I grant you the first point, especially if there is a danger of things getting dropped near it (children's toys, things dropped by older people, middle-aged drunks falling over etc).

[Christian McArdle]

I think you have misunderstood. In a room with a 1kW steady state requirement, a 2kW heater will bring it up to temperature and then, on half power, will be able to maintain it using only a minimum of annoying cycling.

A 3kW heater will bring it up even more rapidly. But then, turned down to

1.5kW, it is over sized and will switch on and off over a 3:2 duty cycle with a period of a couple of minutes.

Christian.

[Bob Mannix]

Well, it's not worth falling out over but (a) you didn't originally stipulate the room had a 1kW heat load and (b), on my 3kW heater at least, you can run the 3kW heater at 1kW, 2kW or 3kW. Generally speaking, more flexibility is better. In any case, in a room which was heatable (ie where you are heating a room and not one person in a warehouse) a convector heater is far preferable, as you get no noise at all.

[Christian McArdle]

Ah. A 3kW heater with 1kW and 2kW options would have no disadvantages over the 2kW one. Mine only has a half and full option. In any case, I was only playing devil's advocate. After all, I voted with my feet (should that be wallet?) and got a 3kW one.

Indeed. I quite like oil filled radiators for this as well. However, you can't beat a fan heater for emergency heat, as they are small and lightweight, so store more easily.

My new shed will have a convector heater, though, (on a frost stat and boost for when I'm in there). It will have 50mm Celotex/Kingspan and double glazing, too, ever since I found out the paltry cost of sealed units. I'm planning to store paint and decent tools in there and don't want them freezing/rusting.

Christian.

[Bob Mannix]

I have a big, old draughty garage that couldn't possibly be heated. Tools are fine, if you give them a quick wipe over with WD40. Oil paints are fine but water based stuff just gets thrown away eventually. A heated shed eh?, there's posh. Better let them know on uk.rec.sheds. I'm sure they will have some OT comments to make.