Interruption of Power Supply

Well then, get it fixed and install a circuit breaker that will protect the wiring next time.

That is, assuming you can figure out what caused the copper wire to melt.

It seems I didnt address my questionare right.

I am trying to find the reason behind wires melting all along the route to lighting switch and why melting drops has dropped only from one point that lead to fire accident.

The main topic is fire accident.

I have gone through Schneider White Paper 18 and made some conclusions on the issue

but still I like to have it discussed with you.

Regards and appreciated

As I said in #3, discuss it with a competent local electrician.

No one here can solve your problems and tell you how to resolve them, without seeing the aftermath.

I will suggest two options, then leave you to flounder.

1. See above. Hire a competent local electrician to explain it to you.

2. See above. Hire a competent local electrician to install a new electrical service that complies with all applicable codes.

The reason for wire insulation melting, most probable one, is loose connection at the light switch terminals. The loose connection leads to heating (high contact resistance giving rise to excessive heat) and consequent melting of PVC. The PVC melt drops are expected to fall near the loose connection point initially and further, depending on the slope of the wire conduit or the wire itself, the pvc melt drops may travel along the conductor before falling down at the appropriate location.

Hope it makes sense.

What many people forget is that circuit breakers do fail. Most of the time a circuit breaker fails but a short circuit does not happen so nobody knows of the failure. This is why regular maintenance and testing of circuit breakers is recommended, although few do it.

Have you contacted your local power provider and ask if there were any faults at their side? Or, asked neighbors probably at different distribution transformer.

Your describing a low voltage scene. It could be caused by upstream line fault of the affected wires and switches.

Say for example a 220Vac, 1A(220VA) equipment if voltage dropped a half, say, 110Vac then load will be sustained under (220VA). Thus, circuit current will be at 2 A. Worst is, if it drops lower than that.

I suggest you conduct ocular inspection on your power panel, there might be rodent or lizard infiltrated the enclosure and connected the buses. Also inspect all connected equipment especially motors. There might be failing equipment/transformer/winding that caused the low voltage.

Circuit Breaker probably failed. They fail both to both open and closed. If it fails open it won't reset or flow electricity. If it fails closed it won't trip for an overload condition when it should.

Have a qualified licensed electrician do the following, at the least. Don't do it yourself unless you are a qualified licensed electrician!

Remove the old breaker and toss it. If the buss bars are aluminum have him coat the contact point on them with an appropriate anti-oxidation paste. Replace all the wiring on that circuit from the breaker panel to the fixture. Check it out to make sure it is correct. Connect the wire to an appropriately sized new circuit breaker and install that in the panel. Check all contacts and voltages. Also use a clamp on amp meter to assure that the appropriate current is flowing to the new bulb. This should be done at the panel. If that doesn't work, fire the unqualified licensed electrician and get the best, probably most expensive also, licensed electrician you can find. The money is a wise investment.

Good Luck, Old Salt

First of all the circuit breaker worked twice. It seems to me the available short-circuit current is more than the circuit breaker short-circuit current could withstand and at third time of interruption the contacts were welded and did not open.

If this is a reliable manufacturer at least 10 kA could be the rated.

I don't think the short-circuit in a lighting circuit could be more than 2-3 kA.

In this case the circuit breaker was damaged or poor manufactured.

Hi,

The kA rating of the CB should be the same as the in both cases you are looking to have the CB operate in a fault situation where the short-circuit is on the distribution network side of the demarcation point. Typically the magnitude of the fault current is this is driven by the fault current at the zone sub-station, and is then moderated by the impedance of the conductors and distance of the installation from the zone sub-station.

Looking at a spreadsheet of maximum fault currents at zone substations on my employer's network the maximum P - G is 15kA and the minimum is 2.77kA (P-P is slightly less in each case).

Hi,

Insidious high resistance L-N fault likely happened the first 2 times due to failing insulation - your lighting point terminals have come loose? - I2R heating! The overcurrent device (OCD) probably tripped on thermal; these events precipitated a short circuit the third time which the OCD could not handle because of:

(i) poor quality OCD

(ii) interrupting capacity of OCD is less than the prospective short circuit current at the point of short circuit.

Regards

Sounds like it was an arcing ground (earth) fault, which if the resistance is high enough, will keep the current too low to trip the circuit breaker, but create heat high enough to melt the wire insulation. It's not as uncommon as one might think, in fact here in the US we now must use new types of circuit breakers called "Arc Fault Circuit Interrupters"(AFCIs) in places where that type of fault can lead to fires.

I always thought arcing grounds are relevant in MV systems!

Can wire capacitance be that significant in LV systems to cause arcing grounds!!

In my opinion this phenomenon is a little bit more complicate. See [for instance]:

http://www.neiengineering.com/wp-content/uploads/2012/05/Arcing-Fault-Current-and-the-Criteria-for-Setting-Ground-Fault-Relays-in-Solidly-Grounded-Low-Voltage-Systems.pdf

I agree with jraef. For instance a 2.5 mm^2 copper will melt in 5.7 sec. for 300 A

and 1.5 mm^2 at 180 A will melt in the same time.

300 A it is 30*Irated of the circuit breaker [Irated=10 A].

According to Circuit Breaker Characteristic Trip Curves and Coordination Bulletin No. 0600DB0105 Data Bulletin [Square D] the circuit breaker will trip in 10 to 30 sec.only.

Sorry! My glasses! It will be for 30 A [3 times Irated] the circuit breaker will trip in

10 to 30 sec. but the 1.5 mm^2 copper wire will melt in 20 sec.