A strange Electrical issue: Pls help

[richardt1808]

Good morning all,

On the weekend, one of the breakers in our house tripped and on opening the panel, I realised it is not a straightforward case of an appliance tripping a breaker. As you can see from the pic, the wire from the second (20A) breaker has actually fried and the insulation has melted. This indicates to me that the heat was coming from the breaker itself, and not a short elsewhere in the wiring. Any opinions from electrical gurus on this ?

Background info: Although the breaker is rated at 20A, the only things running on the entire circuit was a 42" LCD TV, a cable TV set-top-box and two lamps. The house was built by a very reputable Thai building company 4 years ago and we have been in it since day one. The wiring is very professional - European style with proper earthing on all circuits. Do I just replace the breaker and see if everything runs okay ? (obviously we will need to trim the burned section of wire and feed it so that it reaches the breaker).

Thanks for any ideas !

[Rocceao]

It looks like that circuit is drawing a lot more that 20 amps, the insulation has melted when the circuit tripped causing a surge of elecricity to arc as the breaker closed the circuit, what are you running on that circuit?

You need to find out exaclty what is running on that circuit, things to look for is Air conditioner and hot water system as they should have a separate 25 amp breaker each.

what else do you have that will draw more than 20 amps?

Let me know.

[metisdead]

Moved to the Electrical forum.

[bankruatsteve]

Most likely caused by a connection that never was tight or has worked loose resulting in arcing. Need to replace the breaker and cut off the wire several cm after the charred part.

[KhunBENQ]

Your post sounds like the breaker has tripped and you did not notice that some device/appliance is off, no dead plugs?

That would be strange indeed. Are you sure you have checked everything?

Edited November 23, 2015 by KhunBENQ

[IMA_FARANG]

Most likely caused by a connection that never was tight or has worked loose resulting in arcing. Need to replace the breaker and cut off the wire several cm after the charred part.

-----------------------

Obviously, that breaker got hot enough to cause the insulation to partially melt (see the melted bubble in the insulation).

Before you replace the breaker check carefully the breaker enclosure (remove it if possible with mains power OFF} and look inside for any dirt or moisture indications inside.

Sometimes, small insects or even lizards like to hide in such places.

I once found a small burnt (fully carbonized) lizard that apparently had picked the inside of a fuse assembly as his final resting place.

Unusual, but it happens.

[bdenner]

Most likely caused by a connection that never was tight or has worked loose resulting in arcing. Need to replace the breaker and cut off the wire several cm after the charred part.

I think I agree the terminal was not tightened correctly on the CB, the way the yellow insulation appears to have been melted and flowed down the conductor BUT only a short distance.

It was drawing high current at the time which eventually tripped the breaker so I'd be looking down stream at what was on the circuit at the time as the cause of the fault, the damage is a secondary result.

[richardt1808]

It looks like that circuit is drawing a lot more that 20 amps, the insulation has melted when the circuit tripped causing a surge of elecricity to arc as the breaker closed the circuit, what are you running on that circuit?

You need to find out exaclty what is running on that circuit, things to look for is Air conditioner and hot water system as they should have a separate 25 amp breaker each.

what else do you have that will draw more than 20 amps?

Let me know.

Hi,

I traced all of the circuits when we first bought the house. This line runs only to normal outlet sockets in 3 rooms. The following items are the only things that are connected:

LCD TV

VCR

Cable TV Set-top-box

WiFi router

2 lamps

All our AC units, stove, laundry equipment are each on different separate circuits; all with their own breaker. I will double check to see if there are any sockets on the same line which I may have missed, but we were really rigorous during installation of all high-current items, so its definitely nothing like an AC unit.

[richardt1808]

Your post sounds like the breaker has tripped and you did not notice that some device/appliance is off, no dead plugs?

That would be strange indeed. Are you sure you have checked everything?

Hi, thanks for the reply. I did a quick check when it first tripped last night, but I will do a thorough check of every socket and appliance as soon as I get home.

It is rather weird

[Crossy]

I'm with the others suggesting a loose connection fizzing gently away over time.

The MCB is likely toast too. They are not expensive so replace it and trim off the charred length of wire, re-connect.

Do keep an eye on it but I suspect that will be the end of your problems.

[Forkinhades]

Yep, I will echo previous comments, loose connection at the MCB

[Rocceao]

It looks like that circuit is drawing a lot more that 20 amps, the insulation has melted when the circuit tripped causing a surge of elecricity to arc as the breaker closed the circuit, what are you running on that circuit?

You need to find out exaclty what is running on that circuit, things to look for is Air conditioner and hot water system as they should have a separate 25 amp breaker each.

what else do you have that will draw more than 20 amps?

Let me know.

Hi,

I traced all of the circuits when we first bought the house. This line runs only to normal outlet sockets in 3 rooms. The following items are the only things that are connected:

LCD TV

VCR

Cable TV Set-top-box

WiFi router

2 lamps

All our AC units, stove, laundry equipment are each on different separate circuits; all with their own breaker. I will double check to see if there are any sockets on the same line which I may have missed, but we were really rigorous during installation of all high-current items, so its definitely nothing like an AC unit.

Sounds like you have it covered with the appliances on that circuit, seems strange that after 4 years it would go now, as many have said that it could be a loose connection normally a loose connection will give trouble a lot earlier than that.

Do you know if your house is grounded to earth? you can check this by looking for a long copper rod that is buried in the ground close to the side of the house opposite the MCB, it will have a green earth wire conected to the top and connected to the MCB, if you don't this could be a problem esspecially if you had an electrical storm close by and the appliances were on at the time.

[bwpage3]

The purpose of the circuit breaker is to trip before the wire gets damaged.

This did not happen so therefore it was not a direct short to ground.

You can get a relatively cheap current meter that will wrap around the wire and tell you what the amp draw is and then by unplugging things you can tell which outlet the problem is coming from.

If you do not have access to a current meter, you could turn off ALL the power to the breaker box, remove the wire from the circuit breaker and read the resistance with an Ohm meter.

If there is high resistance , then unplug, one at a time, all of the appliances plugged into those outlets to see if the resistance drops down

Do you have a wiring schematic of this circuit?

[bankruatsteve]

Folks, a loose wire connection is the primary cause for electrical fires. That is why it is very important to make sure connections are tight and can't get loose. How do connections get loose? Mainly from temperature changes which will expand and contract the wire. Suspect the connection the OP shows wasn't a lot loose, but just enough to cause arcing. It doesn't take much. And, the arcing may not (probably not) trip the over-current breaker or RCD before extreme damage and FIRE.

Edit: just to add that arcing can happen with Live or Neutral - there is no single suspect for that. Also with soldered connections that have peaks.

Edited November 23, 2015 by bankruatsteve

[T_Dog]

Loose connection is a suspect for sure, but also look for arcing to ground behind or under the breaker. An insect or jinjok could start the corona which would leave the wire scorched like that. 240 volts can support an arc for quite a while as we witnessed with an unterminated extension cord burning up years ago. It was outside and we saw it arc for almost five minutes before the wires melted together and the breaker tripped.

[bankruatsteve]

Loose connection is a suspect for sure, but also look for arcing to ground behind or under the breaker. An insect or jinjok could start the corona which would leave the wire scorched like that. 240 volts can support an arc for quite a while as we witnessed with an unterminated extension cord burning up years ago. It was outside and we saw it arc for almost five minutes before the wires melted together and the breaker tripped.

For sure. But, fault to ground would trip RCD. Without fault otherwise, arcing can and will do a lot of damage before tripping a breaker - if it ever does.

[gk10002000]

Definitely check the power on that wire/circuit with a wrap around or clip on meter. While that circuit may only go to where you say, there may be a short somewhere along the way, anywhere between those outlets all the way up to the box. Wire frying is bad. The CB should have tripped long before the wire fried. I would not be surprised if: 1) your CBs are crap. 2) The wires are under-rated for what they are carrying and what they are rated to carry or are labeled to carry. Quality of wires, fraudulent ratings versus what is printed on the wires, etc. are not uncommon issues. 3) Some poor wiring/connection/construction behind the box or that circuit break that let power get into that wire, perhaps even after the CB tripped.

[wayned]

I need to increase my post count and echo my agreement! Looooooooooooooooooooose Coooooooneeeeeeeecshuuuuuuuuuuun!!!!!!!!

[Crossy]

Wayne, your post count is fine

Once again, the way the insulation is burnt for a short distance from the terminal is a classic indication of a loose connection. You'll probably find the terminal screw is seized (or feels 'funny').

Replace the breaker and re-wire.

QED.

[jacko45k]

Strange that all the wires appear to be the same size, despite different breaker sizes.

Check the wire gauge is sufficient for 20 amps.... the breaker is supposed to trip well below the cable rating. 2.5mm2 or 12/14 gauge (copper) is usual for 20 amps.

It is possible that there was a hot-spot where the cable was connected to the breaker, but what worries me is how such a low load would cause a hot spot.

Replace the breaker with a smaller one more suitable to the load.

A little advanced but normally done after installation....test the wiring with a megga, remembering to unplug every device.

There was likely a fault on the circuit to heat the wires like this, and the breaker failed to interrupt it, was any extra load plugged in, a frequent contender being cheap phone chargers? Another possibility is a loose scrre connection at the breaker, this is a frequent issue here, I call limp wristedness. Check the rest are tight.

Edited November 24, 2015 by jacko45k

[phaykk]

Agree most likely a loose connection, but you do say everything has proper grounds and in the pic at the bottom it appears the one wire you see is a black and white only no ground in it.

[Crossy]

Whether it was an overload that the breaker failed to clear, or a loose connection, the fix is the same.

It's not possible to test MCBs safely in a domestic environment, it's suspect, replace it.

[dotpoom]

It looks like that circuit is drawing a lot more that 20 amps, the insulation has melted when the circuit tripped causing a surge of elecricity to arc as the breaker closed the circuit, what are you running on that circuit?

You need to find out exaclty what is running on that circuit, things to look for is Air conditioner and hot water system as they should have a separate 25 amp breaker each.

what else do you have that will draw more than 20 amps?

Let me know.

He did point out what was on the circuit....seems very very light stuff?

[Thaimike370]

Hello dotpoom. Your problem was probably just caused by the breaker screw being loose. Trim the burnt wire then fit a new breaker, check and tighten all of the other wires.

[DiDiChok]

I agree with the loose screw theory. It's a fact that as the supply is alternating current, the screws come loose over time as they're undone by the vibrations in the wire caused by that alternating current. This is particularly bad in offices where there are a lot of computers using switched mode power supplies and every screw in the box comes loose. Periodically, somebody has to go around and tighten up all those little screws in the fuse box, sockets, switches and lights.

All new installations should be checked after a couple of years as the screws always come loose and the copper wire anneals. Looks like it's time to do that everywhere now and to get a new breaker fitted after the circuit has been checked for leakage.

[gandalf12]

It could be, just really thinking out loud, that at some time a voltage surge from lightning has destroyed the breaker. If not it has not been functioning correctly anyway. Unlike fuses which can stand 100% overload a breaker will trip within milli-seconds with an overload of around 10%. To fry the cable indicates it was not working.

I would change the breaker and have the cables connected to it replaced. Even if they look ok the insulation resistance of the cable could be badly damaged and should be replaced.

Also when replacing the cables get th Core to Earth resistance measured. It should read infinity or open circuit.

Edited November 24, 2015 by gandalf12

[sandyf]

I'm with the others suggesting a loose connection fizzing gently away over time.

The MCB is likely toast too. They are not expensive so replace it and trim off the charred length of wire, re-connect.

Do keep an eye on it but I suspect that will be the end of your problems.

I would tend to agree. Had it been a load fault the breaker would have tripped or if stuck there would be indications of overheating elsewhere, in particular within cable looms.

In this case it would appear the breaker tripped due to heat from a bad connection rather than excess current.

[05daytona]

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)

[Urbain]

There is/was a massive short circuit somewhere between the breaker and the neutral or the earth (ground). proceed with great care looking for this short circuit. Start by disconnecting the circuit from the breaker (the melted wire). Disconnect everything from the breaker circuit (TV etc...). Then inspect de disconnected appliances for a short ciircuit. Then inspect the different power outlets, first make shure there is no remaining power on line, neutral and earth! Measure the resistance between the line and the neutral and between the line and the earth at each power outlet and finally between the melted end and the neutral and the earth. Good luck.

[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.