1st year apprentice

[Dave Liquorice]

Only when it hadn't been un wound...

[Cursitor Doom]

They wouldn't be if they knew the history behind it. In fact they'd laugh their nuts off. Just search on "Frankfurt School" and read about the congenital mental cases who dreamed it all up.

[ARW]

[543dsa]

Because things have changed radically for the non thick now so they are much less likely to end up as apprentices now.

[tabbypurr]

1. I don't know where you'll find a ref for it. It's hardly news that the hotter for more of the time a cable runs the less its life is. Even in the 1920s folk skilled in the art were entirely familiar with that.
2. It is far from made up. I can only conclude you aren't familiar with how domestic cabling actually operates
3. I have no reason to regret what I've explained.

Your turn to waste time.

NT

[tabbypurr]

It's rated nearly 30A depending on the installation method. And the currents flowing round the 2 legs are usually not balanced. And etc etc etc.

often it does

NT

[ARW]

The maximum CCC of 2.5mm T&E is 27A and it must never be installed on a ring where the installation method drops the CCC below 20A.

[John Rumm]

70 degrees is usually given as the maximum *conductor* temperature for PVC, where it can still be expected to provide at least 20 years of usable life. It will run hotter without catastrophic failure, but will be damaged ever more quickly depending on how much hotter and for how long.

The adiabatic equation for calculating cable survivability assumes that the fault will occur with the cable already operating at its maximum conductor temperature, and that the final conductor temperature on clearing a fault will remain under the "admissible limiting temperature" (its this and other parameters that are used to devise the k factor[1]). That is specified for PVC as 160 degrees. So its generally assumed that a very brief flash to 160 degrees will not cause failure of the cable.

[1] Which is defined as "a factor taking account of the resistivity, temperature coefficient and heat capacity of the conductor material, and the appropriate initial and final temperatures."

[John Rumm]

Did you get any say in choosing them though? I suspect Adam's would have far fewer limitations if he were given the chance to vet them first...

(and a few may run away before even starting!)

[Cursitor Doom]

No probs. I'd secure the end of the tape to the tip of my dick, then flick through Penthouse. Sorted.

[John Rumm]

A cheap and low quality material used in inadequate quantities for the manufacture of many mechanical and electrical items made in China.

[John Rumm]

Yup that ties in with this (not particularly easy to read) fuse response curve for a BS1362 fuse:

That suggests for a 300 second duration an overload of approx 21A to 30A should be enough to blow it.

[John Rumm]

At which end were you observing the lights dimming?

Even if at the shed end remember the total supply impedance is not only made up of the SWA, but also the house wiring to the CU, and the supply impedance. So it would be quite normal to see a few volts dropped on the end of a long run. Enough to be visible on incandescent lamps.

For example, in this house our supply impedance is about 0.24 ohms. Say I had 30m of 6mm^2 cable, that would add another 0.185 ohms, so 0.42 total. So a 13A load would give a 5.5V drop at the end of the cable, and over 3V even measured at the CU.

[Fredxx]

While I agree with much you say, constant k is not defined as a temperature but a derivative of temperature increase (a function of the square root of dT)

[John Rumm]

I don't really understand what you are getting at...

I can't really find any way of reading the wording "a factor taking account of the resistivity, temperature coefficient and heat capacity of the conductor material, and the appropriate initial and final temperatures." as "k is defined as a temperature". Can you?

(And the wording is taken straight from BS7671)

[Dave Plowman (News)]

True. This is the problem in village halls etc. Dunno just how you'd prevent it happening.

[Dave Plowman (News)]

Cable in the 1920s didn't have PVC insulation.

[Dave Plowman (News)]

True. But not to the extent where one becomes overloaded.

[Dave Plowman (News)]

In the BBC, no. All chosen by HR - although a board had an appropriate person skilled in the 'trade'.

At Thames, yes, in a way. Our HOD was a superb manager, and involved all his department in as much as possible.

I remember we made up a series of boxes - all looking much the same. A radio tuner (etc), amplifier and speaker, but marked as such. With a variety of leads - not all would plug in. And asked an applicant to get them working. You'd be surprised how many couldn't.

[Marland]

Use cable tidys shaped like the one in this picture?

The cable may still get warm but not so much not being confined tightly in a drum shaped container with no air flow.

I made similar shaped ones for my leads out of some 25mm x25mm wood that was lying about ,the leads being made from cable and hardware of a quality I could assess when purchasing the components separately. Also my personal preference is for rubber sheathed cable finding it lays down tidier and the cable drum as supplied on most ready made leads even when the cable is unwound can be a large lump on the end of the lead getting in the way.

GH