Fire to Fluorescent lighting fixture

[Pham Van Hung]

Hi.

We've just experienced a fire to one of the fluorescent light fixtures and need your helps for investigation of root cause.
8 twin ligh fixtures 2x40W using magnectic ballasts are connected in parallel (so totally 16 lamps connected in paralell).
Actual measured current of a lamp branch is 0.3A.
Wire of a branch is 1mm2 solid wire, and cable of supply line is 2x4mm2 stranded wires.
One 16A inverse time MCB to switch on and off the 16 lamps.
No junction box outside the fixture for intermediate connections, in stead plastic terminal blocks are used inside light fixture for connection and jump from fixture to fixture). The terminal block and its associated wires is located about 30mm from one ballast.
Electric wires were inside the loom tubes (pls see my attachment)
At the time of the fire the 16A MCB was tripped.
Checking other fixtures we found some cases that:
The branch wire inside light fixture touched the ballast and sticked to the hot ballast since the wire sheath was melt by heat and acted as an adhesive to keep the bare core of wire in contact with the ballast case. This caused fault current of 0.7A in the branch circuit of the lamp with fault. The 0.7A did not trip 16A MCB, and monitoring of ballast iin this case showed increasing temperature.
I attach herewith the PDF file for your imagination.
Any advices on possible root cause are appriciated.

 

[Volta]

I don't think that we can know from here, the pictures are hard to interpret. But how is it that you figure the fault current was only .7A?

I could speculate that a connection to a terminal may have had high resistance and the spiral started from there, but that is purely a guess. If the ballast is normally too hot for the insulation type used, that would be poor design on somebody's part.

As an aside, is it standard practice in your area to protect a 1mm2 wire at 16A? Seems close to being protected, but a little small for my liking.

 

[Pham Van Hung]

I don't think that we can know from here, the pictures are hard to interpret. But how is it that you figure the fault current was only .7A?

The .7A fault current was intentionally arranged by us. After the fire, we checked all lights and found line wire touched ballast case. We took it out and attached it again by purpose to simulate a fault condition.

I could speculate that a connection to a terminal may have had high resistance and the spiral started from there, but that is purely a guess.

Yes, poor connection is the most likelihood as one of the senior member in this forum advised me via email.

As an aside, is it standard practice in your area to protect a 1mm2 wire at 16A? Seems close to being protected, but a little small for my liking.

The 1mm2 is the wiring through one lamp only whose actual current is 0.3A and this 1mm2 wire is orgininally pre-wire by light fixture manufacturer. The supply wires are 2x4mm2.

 

[Volta]

The .7A fault current was intentionally arranged by us. After the fire, we checked all lights and found line wire touched ballast case. We took it out and attached it again by purpose to simulate a fault condition.

Ok, but something must have limited the current flow during your simulated test. A much higher current flowed during the original fault. You will agree, as the 16 amp breaker was found tripped.

Yes, poor connection is the most likelihood as one of the senior member in this forum advised me via email.

Guessing only, with some squinting at the pictures, but it seems like the terminal block experienced the most heat.

The 1mm2 is the wiring through one lamp only whose actual current is 0.3A and this 1mm2 wire is orgininally pre-wire by light fixture manufacturer. The supply wires are 2x4mm2.

Gotcha. When you say 2x4mm2, does that mean paralled wires? Are dual 4mm2 wires used for each ungrounded conductor path?

 

[Pham Van Hung]

Ok, but something must have limited the current flow during your simulated test. A much higher current flowed during the original fault. You will agree, as the 16 amp breaker was found tripped.

I think the resistance of ballast case insulation material plus fixture case resistance + resistance of neutral conductor prevented the current. In my opinion, the 16A CB was tripped after the fire took place which melt the supply cables and made direct contact bwt line and neutral.

Gotcha. When you say 2x4mm2, does that mean paralled wires? Are dual 4mm2 wires used for each ungrounded conductor path?

No it is a wire for line and the other is for neutral.