How many 2.5mm T&E into a 13A socket?

[Major Scott]

On Tue, 02 Apr 2013 18:38:45 +0100, harry w= rote:

I use LEDs (and CFLs until they've all worn out). I've got 60W in this = room, which is just LEDs. Ten 6W LEDs (50W halogen equivalent). 8 room= s, that's up to 480W, even when I get everything changed to LED. All th= e lights are automatic, so it does happen that they are all on at once i= f I'm moving around the whole house. I like it to be as bright as a sun= ny day :-)

-- =

The easiest way to find something lost around the house is to buy a repl= acement.

[Major Scott]

You think fuses are a bad idea? We were using them for decades before these health and safety morons appeared.

[Tim Watts]

On Tuesday 02 April 2013 15:32 Major Scott wrote in uk.d-i-y:

Then you really do not understand.

Final circuits rated at 32A or less in domestic properties are required to disconnect from the supply in Anyway, if the current limit is less, you don't need as low an impedance

Correct. For a given tripping time and a fixed characteristic (breaker or fuse type) the required current to give that tripping time is a fixed ratio over the nominal rated current. But in your case, that assumes that the breaker is a 0.5A breaker or fuse. Claiming the design current of the circuit is 0.5A and then protecting it with a 5A fuse does not work.

Irrelevant.

[Tim Watts]

On Tuesday 02 April 2013 18:48 Major Scott wrote in uk.d-i-y:

The you should probably ask your electricy company for a 150A supply depending of whether you have an electric shower and cooker.

And a road with 100 houses should be supplied with 5000A 3 phase cables.

etc etc.

[Major Scott]

Comparing two cable installations, where the cable is on a circuit protected by a fuse rated the same as the cable. One is 10A and one is 5A.

If you double the cable's resistance (10A to 5A cable), you halve the short circuit current through that cable, but you've also halved the fuse rating, so the time to blow the fuse will be the same.

People with fuses aren't so worried about quick trips.

[Major Scott]

No, it's fine as long as there is adequate protection. The electricity board assumes I will never use more than 100 amps. But if I did, the fuse next to the meter would blow.

But assuming nobody will ever draw 26 amps from a double socket, and having no protection if it did happen, is daft.

[Alexander Lamaison]

Unless the circuit was never used it doesn't show that. What it shows is that the plastic couldn't handle whatever temperature the conductors became under load with an ambient temperature the same as the radiator. This could be higher than 100C depending on flex resistance and fan load.

Alex

[Alexander Lamaison]

I mean when you're totting up the total load to assess whether the main cutout is sufficient. OSG says use "100% of current demand of largest circuit + 40%". So do you just say design current 32A for ring on 32A MCB so sockets = 32 + (12.8)n?

Alex

[Major Scott]

I forgot to mention the fan was switched off. Most people don't use a radiator and a fan on the same day.

Mind you the local council doesn't seem to realise this, a woman in a council flat gave me her ceiling fan because she was told she mustn't have one in the same room as a gas fire in case it blows it out. She said she'd never use both at once, but he didn't listen. Then she said what about an open window, and he still didn't listen. I would have removed the fan temporarily while he fixed the fire, but she didn't. So I got a free fan.

[ARW]

So you live in a caravan?

[Alexander Lamaison]

You seem to be thinking of the items in an electrical installation as having ratings indicating a magic boundary: a '30A cable' that's protected by a '30A fuse', in your mind, is good while a '20A cable' protected by a '30A fuse' is bad.

That's not how it works. Think of the ratings on these things as more like names than numbers. You can't match circuit components and protection using the number on the back, like painting-by-numbers.

In case you are still sceptical, consider the difference between a 30A rewireable fuse and a 30A cartridge fuse which have different protective 'strength' (a 30A rewireable fuse has about the same ability as a 22A cartridge fuse - if they existed).

Alex

[Alexander Lamaison]

I think this sums up your misunderstanding. A 100A fuse would not blow just for going over 100A. You have exceed its rating continously for a period of time. For example, a 100A fuse must not blow when overloaded at 160A before the overload is carried for _4 hours_!

That's exactly what happens throughout the system, you've just never realised. There is no protection that kicks in when you exceed either the rated current of the 20A socket *or* the rated current of any circuit in your home. The protection in both cases kicks in some time later if you continue to exceed the rated current and it's safe because it was specifically engineered that way.

If I could say only one thing it would be not assume you can compare the ratings of things directly. They're not colour-codes.

Alex

[John Rumm]

Buy MK ones then - they claim to test with 2 x 13A loads.

Look at the current draw profile and you will find none of them present continuous 13A loads. Many appliances of that nature are designed with

10A maximum loads, and that will be reduced over time by the action of the thermostats.

Which re-enforces the point really. If you are buying for your own place and need a few dozen, then you can splash out a hundred quid extra on the higher quality ones. If on the other hand you are purchasing for a new housing estate, the prospect of saving £20K by going for an item that in all practical purposes will work just as well, is attractive.

Have a look round your house - you will likely have a range of accessories that don't meet the standards you claim to subscribe to, and yet here you still are.

[Alexander Lamaison]

Like I said yesterday, sockets aren't firecrackers. They don't burst into flame in indignation that you exceeded their rating. Are you running the elements of all three machines on full, simulatanously for

10 hours? No, you couldn't convince the machines to do that even if you wanted to.

Its certainly your right to dream.

Let's imagine this socket somehow protected 20A by a 20A fuse (your main complaint is that it isn't) and that you convinced that lot to run at

26A for an hour and a half contiunously (you couldn't). That would not even begin to tickle your 20A fuse - it would never blow.

Exactly. The ones rated at 20A are pennies. The MK ones, apparently rated at 26A, are not.

Alex

[John Rumm]

If you had two socket circuits, then yes.

Note that the OSG guidance has not changed in many years though, and modern usage profiles have shifted dramatically in that time.

100% of the kitchen circuit, and then %20 of the next and ignore the rest might be closer these days.

Some of this is discussed here:

[John Rumm]

Yes of course...

Standard building materials are not combustible at that temperature...

Note also that is the conductor temperature. There will be a temperature gradient across the insulation, so the touch temperature of the insulation on the outside will be lower.

[John Rumm]

What is your wall made out of? What temperature will it spontaneously combust at?

[John Rumm]

No, we think people who put faith in fuses without also ensuring there is adequate PFC to operate them, are either ignorant or morons.

[John Rumm]

Sorry, typo, 20A in clipped direct.

[Major Scott]

Put a match to your wallpaper. Or plasterboard.