Cable ampacity

regs as 16A if clipped to a wall, 8A buried in insulation. Why the difference? Is PVC just a much better thermal conductor than air? T he T&E has far more PVC than the single.

NT

Reply to
tabbypurr
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** All to do with the expected temp rise and resulting deterioration of the PVC in use. T&E has extra insulation & physical protection for the PVC on the conductors and if air can circulate freely round it gets a higher curre nt rating.

Singe flex cables are used in ceilings for lighting circuits where the ambi ent temp can be high and they may be covered in insulation material, so a d e-rating is applied.

You must have seen PVC coated wires that have run hot for a long time - eve ntually the insulation blackens, becomes brittle, cracks appear and it fall s off.

.... Phil

Reply to
Phil Allison

he PVC in use. T&E has extra insulation & physical protection for the PVC o n the conductors and if air can circulate freely round it gets a higher cur rent rating.

bient temp can be high and they may be covered in insulation material, so a de-rating is applied.

ventually the insulation blackens, becomes brittle, cracks appear and it fa lls off.

right, cheers

NT

Reply to
tabbypurr

On Thu, 10 Dec 2015 17:02:25 -0800 (PST), snipped-for-privacy@gmail.com Gave us:

"Buried in insulation" means the heat generated has nowhere to go. Not as good as in a tray run or "clipped to a wall".

Not from the UK so I do not actually know, but this is what I would guess is the reason.

Reply to
DecadentLinuxUserNumeroUno

On Friday, 11 December 2015 04:21:57 UTC, DecadentLinuxUserNumeroUno wrote :

n.

I think you've misunderstood the question. Why the difference between the s ingle 6-10A rating and the T&E 8-16A. The significant difference is 10 vers us 16A.

NT

Reply to
tabbypurr

On Fri, 11 Dec 2015 06:04:38 -0800 (PST), snipped-for-privacy@gmail.com Gave us:

Ampacity in commercial and residential wiring specs is not about what the physics are in what a given gauge of copper can handle before fusing open. It is about heat and fire prevention.

So an armored run will be permitted to carry more than an open exposed run.

Does that help?

Reply to
DecadentLinuxUserNumeroUno

this has to be transferred into the environment. The thicker the conductor/cable insulation and if the cable runs through some insulation material, the harder it is getting away of this heat, while keeping the conductor temperature sufficiently low for the conductor itself, the conductor/cable maximum temperature and the maximum building material temperature.

A T&E is in fact carrying twice the current (L+N), so at 10 A, the current would be 10+10 A and cable dissipation 3.4 W/m.

That UK building regulations seems a bit high, in other European

Is the UK still using ring mains with say 35 A fuses at the end of the ring and smaller, load specific fuses at wall plugs ? Wouldn't the ring mains require much thicker conductors to trip such big fuses reliably ?

Reply to
upsidedown

It's YOU who constantly misunderstands the ANSWERS, tabbytroll. You would have posted this question to uk.d-i-y where it would be more appropriate, but since your rep there for trolling is so bad you're trying your luck here instead, I see...

Reply to
Julian Barnes

On Friday, 11 December 2015 14:50:57 UTC, DecadentLinuxUserNumeroUno wrote :

ote:

tion.

ot

e single 6-10A rating and the T&E 8-16A. The significant difference is 10 v ersus 16A.

I thought ampacity was determined more by insulation life expectancy with p vc. This gives temps far below any fire risk. And I think I've got it.... w ith house wiring those max figures aren't often reached/exceeded, so the ca ble can get a bit hot at times but still last well. OTOH the single flex mi ght be used in any situation at all, so needs to be rated for continuous fu ll current use.

NT

Reply to
tabbypurr

that's true if pvc is a worse thermal conductor than air. I don't know but suspect it's better rather than worse.

ing regs as 16A if clipped to a wall, 8A buried in insulation.

? The T&E has far more PVC than the single.

30A fuse or 32A breaker supplying a ring of 2.5mm^2 cable feeding an unlimi ted number of sockets (limited large floor area). Plugs all have 13A or low er fuses. So every socket is fed by no less than 5mm^2 of copper. IIRC perm itted overcurrent clearance time is 0.4 seconds for sockets, 5secs for ever ything else.

The system is safer, cheaper and more reliable. It has such upsides over ra dial that it's odd that no other country has copied it.

NT

Reply to
tabbypurr

Anyone can see I wasn't asking about the effect of burial in insulation, which is quite obvious.

I don't think ukdiy a good place to ask such things personally, far too little electronics knowledge. It's a house maintenance group.

NT

Reply to
tabbypurr

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