Safe temperature to run Switch Start Fluorescents

[Ash]

The ballast would withstand one day of high ambient temp no worse than it would withstand one day of stuck starter

Good point on the PF cap - It might have had a one-off bigger self healing event, possibly pushed on by the higher temperature

And it might have been a spider getting into a terminal somewhere in the fitting and igniting an arc, tho in this case it would likely be an L-E short, so trip the RCD before the fuse



In the last significant heat wave we had, the ignition coil pack in my car failed the next day after a day in which i had a long ride during peak heat. The secondary winding of one of the 4 coils changed resistance from 4.2kOhm to 3.9kOhm (300 Ohm of windings became shorted turns) and the engine started misfiring

It is all rated to work at such temperatures (when new), but the aging coil pack (with 130K km on it) probably had insulation going brittle inside, and the higher heat tipped it over

Now, a car ignition coil have a secondary winding made of really thin wire (4.2 kOhm resistance with copper wire) with really thin insulation, and producing voltages in the 10's kV range

Something like this can fail slowly - It might have had a single first flashover during the hot ride, after which it had more single event flash overs every now and then (which would make single skips in the engine, unnoticed as long as its one-offs), and took another day to fail permanently

A FL ballast have much lower voltage, so if FL ballast insulation degraded to the point where it flashed over, it means there is no insulation left - It will be more likely to fail permanently immediately

[Oliver]

I think 40c temps would be fine to be honest, but if they are particularly hot running ballasts to start with, then I'd be more concerned. My 2 x 18w fittings with a single ballast run scorching hot at the best of times!

My two sign lights outside are in full sun and during the 40c heatwave we had, the little Tridonic ballasts were measured at 100c! They run 24/7 and continue to work fine to this day. If the tubes were rectifying at the time, I think they would've got quite close to the 120c limit though.

One way to try and reduce the temps of your ballasts is to maybe install the fittings onto some thick steel box section to try and pull the heat away from the ballasts or leave the gear tray covers off.