A strange Electrical issue: Pls help

[gandalf12]

I would say that you would probably be better off getting an electician to check it out. Someone who can check both your voltage and also the Current being drawn on that circuit.

I would imagine that the appliances you have stated would add up to around 500 or 600 watts.

If you use Ohms law,

Even if you said that circuit had 1000 watts @ 240v which would equal only around 4 amps.

Definately not enough to heat that conductor in question.

Something is very loose....Or that circuit is drawaing a lot more than 4 amps.

Ohm's Law defines the relationship between power, voltage, current, and resistance. The various possible formulas for Ohm's law are as follows.

Where

P = power in watts

E = voltage in volts

I = current in amps

R = resistance in ohms

I = E/R

I = P/E

I = sqrt(P/R)

Standard letter for Voltage is V not E

[Crossy]

I would say that you would probably be better off getting an electician to check it out. Someone who can check both your voltage and also the Current being drawn on that circuit.

I would imagine that the appliances you have stated would add up to around 500 or 600 watts.

If you use Ohms law,

Even if you said that circuit had 1000 watts @ 240v which would equal only around 4 amps.

Definately not enough to heat that conductor in question.

Something is very loose....Or that circuit is drawaing a lot more than 4 amps.

Ohm's Law defines the relationship between power, voltage, current, and resistance. The various possible formulas for Ohm's law are as follows.

Where

P = power in watts

E = voltage in volts

I = current in amps

R = resistance in ohms

I = E/R

I = P/E

I = sqrt(P/R)

Standard letter for Voltage is V not E

You can use E or U too.

Depends upon circumstances, but in our case, yes, using V is correct and non-confusing.

EDIT Using V for both the quantity and the unit is unusual (or possibly unique) in the SI system.

[gandalf12]

Can those advocating a dead short or massive overload somewhere please explain whey the incoming MCB didn't open.

Even if the circuit MCB was welded the incomer provides the second line of defence.

The MCB is probably 63A or there abouts. A surge of 40A say would not trip that just the downstream breaker. In this case looks like it did not exceed the capacity of the downstream breaker

[bankruatsteve]

Great. I have my entertainment for the day. Thanks all.

[Crossy]

Can those advocating a dead short or massive overload somewhere please explain whey the incoming MCB didn't open.

Even if the circuit MCB was welded the incomer provides the second line of defence.

The MCB is probably 63A or there abouts. A surge of 40A say would not trip that just the downstream breaker. In this case looks like it did not exceed the capacity of the downstream breaker

But a 40A surge wouldn't do that to the cable either

EDIT sod it - it was a surge / overload / mystery fault. Read my signature. Then replace the damaged breaker and trim back the cable.

EDIT 2 some interesting reading about loose connections http://www.thecircuitdetective.com/melted.htm

[gandalf12]

Can those advocating a dead short or massive overload somewhere please explain whey the incoming MCB didn't open.

Even if the circuit MCB was welded the incomer provides the second line of defence.

The MCB is probably 63A or there abouts. A surge of 40A say would not trip that just the downstream breaker. In this case looks like it did not exceed the capacity of the downstream breaker

But a 40A surge wouldn't do that to the cable either

EDIT sod it - it was a surge / overload / mystery fault. Read my signature. Then replace the damaged breaker and trim back the cable.

Are you sure about that? A surge like that would do it

[Crossy]

Can those advocating a dead short or massive overload somewhere please explain whey the incoming MCB didn't open.

Even if the circuit MCB was welded the incomer provides the second line of defence.

The MCB is probably 63A or there abouts. A surge of 40A say would not trip that just the downstream breaker. In this case looks like it did not exceed the capacity of the downstream breaker

But a 40A surge wouldn't do that to the cable either

EDIT sod it - it was a surge / overload / mystery fault. Read my signature. Then replace the damaged breaker and trim back the cable.

Are you sure about that? A surge like that would do it

Yes I'm sure.

BKK Cable 2.5mm² THW is rated at 29A in air (70C insulation), at 50A it is getting very warm, but nowhere near smoking.

Anyway, a 'surge' isn't going to get enough energy into the copper to heat it up much, it would need a sustained overload for hours. These cables are massively over-rated to prevent small (100%) overloads from starting fires.

The damage footprint is a classic loose connection, insulation burned back from the hot (very hot) arc point, no damage to the insulation further down (heat dissipated to atmosphere) indicating that the heating was localised, not along the length of the cable as overload heating would be.

EDIT A not particularly scientific experiment here http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=58432 (note the test was with a 0.75mm² flex), don't bother reading past the first page, it gets a bit 'handbags at dawn' (like many TV threads).

[TungnaaTom]

I've seen this before. The connection under the screw is not good, and it heats up, even if the load is less than what the breaker and wire are rated for.

The usual cause is that the screw was not tightened down enough. The second cause is that the copper wire was heavily oxidized before the connection was made.

Strip back the wire to where the insulation is not burned, like another poster pointed out, and if the wire is black, then use a fine grit sandpaper to remove the oxide. The colour of the exposed wire should be shiny copper.

The screw assembly of the breaker will be oxidized & melted, so replace the breaker with a new one.

And finally: TIGHTEN DOWN THE SCREWS ON ALL THE OTHER BREAKERS! I've worked a few industries in Asia, and noticed that Asians are afraid to properly tighten down screws in every industry. I've had wires fall out of terminal blocks after I touched them! In your case, if the electrician did not tighten one properly, chances are he did not do the rest either!

Edited November 24, 2015 by TungnaaTom

[realenglish1]

Hey I have a lot of loose connections but so far my brain is still working no shorts

[Crossy]

Hey I have a lot of loose connections but so far my brain is still working no shorts

Your choice to go commando has no relevance to this thread

[richardt1808]

Thanks for the great suggestions guys.

We had an electrician over who was great. He replaced the breaker with a 10A one and did current draw test, plugging items in one-by one. The wife forgot to ask him if the screw on the old breaker was loose, but I opened up the panel again when I got home to check the others. He must have tightened them all as they were all rock solid. The receptacle in the old breaker was black and slightly pitted, so It looks like it was indeed a loose screw.

Many thanks !

[Forkinhades]

Case closed, so thread closed to stop all this nonsense.

If anybody wants this reopened then PM me with the reason why.