How many 4 x 36w Mods on a 6 amp circuit

[RobTDCI]

We have a problem at work where one of the lighting circuits with a 6 amp breaker keeps tripping after hours of usage. The circuit has nine, 4 x 36w magnetically ballasted mods. We have tried having fewer lit and it seems OK then and seems strange that it should start giving problems now have been in this building for 12 years. Is it possible that the circuit is slightly overloaded? It's right on the max according to my calculations including magnetic ballast losses but I don't trust my simple take on things.

[HIDLamp]

My work has 18 4x18W magnetic mods on one breaker and they seem fine (haven't examined to see what the breaker is though)

[Kev]

MCBs can weaken when used on the max over a period of time had it a good few times.
Had to change a 16A triple pole a couple months ago that was tripping on 9A when the water heater was pulling 12 per phase. Old dorman smith

[FrontSideBus]

Power factor correction capacitors degrading over the years and causing the circuit current to gradually rise?

[Slyspark]

I've seen this before where a ballast is on the verge of smoking out. Kept on tripping, yet there was never anything obvious and it would just randomly do it after being on for hours. I discovered the best way to find this is to insulation test between phase and CPC at high voltage (500 or 1000V) and generally that's enough for the ballast to go into meltdown about 5 mins after you restore the power. It's one way of finding the fault I guess....

That, or as Kev has pointed out above, MCB's do sometimes just wear out, so worth replacing it, or maybe switching the MCB's over on 2 different lighting circuits and see if the fault moves with the MCB.

[RobTDCI]

Thanks for your advice guys, all good as always!

It hasn't done it sonce Wednesday, but one of the rooms affected has no Window to outside, so its a bit more of a problem than it otherwise would be. We will probably try swapping an MCB first but failing that, we will have to try and find a decent electrician, easier said than done.

[Kev]

Or even easier you would most likely be fine to bang a 10A in there