Repairing nick in 2.5mm cable

[Mike Harrison]

You have to look at the figures in more detail before making such assertions, and take into account that the resistance of the joint is initially very small compared to that of the load. If you draw a graph of power dissipation in one of 2 series resistances (joint plus load) at constant supply voltage, you will see that it peaks at the point where the two resistors are equal, so until the joint resistance equals that of the load (by which time you are in serious trouble), power dissipation, and therefore heat, will increase with increasing joint resistance.

[Mike Harrison]

Correct. Then oxidisation kicks in to make things exponentially worse.

[Frank Erskine]

I didn't mention joints - I was talking about a nicked wire.

[Dave Liquorice]

I don't think that in itself would be a problem but the whole picture includes the earths magnetic field. Thus any current carrying conductor will have a (small) force excerted on it.

You can feel the vibration in cable carrying a 50A or so without any trouble.

[Newshound]

Exactly; plus, if it gets loose enough to get any arcing that will rapidly cause oxidation and runaway heating.

[david lang]

How difficult is it to cut out the damaged section of cable and use 2 x junction boxes to insert a new piece? Why not do the job properly?

Dave

[<me9]

It's a load of B******s.

[<me9]

When you are in a hole stop digging.

[<me9]

Tea leafs rather than Nutmeg?

[<me9]

As long as the conductors are not significantly damaged then it should be fine. Otherwise either replace the section of cable or join it in an accessible junction box.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Bob Watkinson" saying something like:

Honestly; I don't think I've read such a load of cobblers for years.

Utter, utter, s**te.

[John Rumm]

although I doubt the

effects, both environmental

the floor.

will cause a

over time, which will

contact surface,

likely to start a fire.

At last common sense (and the laws of physics) prevail! ;-)

[John Rumm]

!

I think I would strip some of the outer insulation leaving the three wires accessable, fold the cable at the damaged bit and slide heat shrink over each of conductors. Shrink them, and then use a wider heat shrink over the whole cable.

[John Rumm]

If you want ot go this route, and if this is to be a join in an unaccessabel place it would be better to not use screw connections. Crimps and heatshrink, or crimps in an insulating box would be better.

[charlieB]

No

For the local heating effect at a poorly made connection, dissipated power, P=V*I

However, I is the current is the current flowing in the ring/spur and has nothing to do with the impedance of the joint.

V is the voltage dropped across the impedance of the poor connection, R, due to current flowing in ring, I.

Power dissipated in poor connection, P= I*I*R

The larger the impedance of the poor connection, the more heat will be dissipated locally.

[Chris Bacon]

See if you can get a "small tools handling" course in at some time.

[mungoh]

I've found it invaluable to keep a couple of those cheap nightlights in my toolbox to help ascertain when mains sockets are powered.

Go down your local pound shop and pick up a packet of one or two neon nighlights and store these in your toolbox.

Saves scrabbling for some electrical appliance to use to test a socket.

Mungo

[Sadly]

There is only one answer to this: "You are Doctor Drivel and I claim my =A35"

[Mike Harrison]

If the conductor is not damaged, inserting 2 additional junction boxes would be far from 'properly' in terms of reliability and potential safety.

[Andy Wade]

I suggest you stop, cease and desist from giving advice on any electrical topic forthwith as you're talking complete bollocks.

Loose connections and nicked wires (reduced cross-sectional area) lead to development of localised hot-spots due to resistive heating. The amount of heat generated is directly proportional to the contact resistance of the joint and to the square of the current flowing. Frictional heating due to vibration (which would be at 100 Hz, by the way, not 50 Hz) might contribute a minute amount of additional heat, but is certainly not a material factor.

Clue: how do fuses work?