I work at a waterpark where we sometimes do night swims in the summer. Most of the park is lit from 7 stadium light poles containing a total of 44 1500w metal halide lamps. Each pole gets 2 of the 3 phases for 480v at each ballast. The installation is 21 years old and the ballasts have become unreliable. They are planning to switch to LED for reliability (the lights are not used enough to ever pay back on costs). One night I closed the contactor circuit as usual, the lights starting striking and warming up, then sparks shot from the top of one of the poles, probably a phase to phase short at a ballast, tripping not just the 35a breaker feeding that pole, but the 200a breaker in the MDP feeding the whole system. And we can't do anything for 10 minutes while the lamps cool down.

It is critical that full loss of lighting does not occur when we have people in the water, because they could get hurt (or possibly drown) trying to exit a crowded pool in the complete darkness. It should be much easier to drive the LED lights from emergency power than HID, but what's to stop the main panel breaker from tripping if a fault at one LED driver occurs?

It is not related just to LEDs, but a general rule is, you have all the installation split among multiple circuits with independent breaker on each circuit. In that way you may isolate the one circuit with the faulty fixture, yet have the remaining ones still operating.
Your description sounds to me like there is just a single 3-phase circuit (because of the single breaker unit it means it is to be treated as a single circuit), so in no way it is capable to provide any redundancy at all.
However the LEDs will still be a safety improvement there over the HID: The individual ballasts do include a fuse (or some equivalent device), isolating the damaged ballast from the mains. So although it may trip the common breaker when the fault occur, by resetting the breaker you have most of your lights back on, without the 15 minutes restrike gap. It means still some minute of darkness (till you get to the breaker and reset it), but still that would be way shorter, so the shorter darkness will way less likely erupt into the deadly panic among the visitors.

And make sure your PA system is working, so you are able to calm the crowd down (and better to take some training in that)...

With a "critical" system such as this-you should have a fuse in each fixture so if one faults-it won't bring the whole light system down.

HID lamps with a twin arc tube would mean that you could make a hot restrike.

The sparks that shot from the pole were in all likelyhood not a ballast failure, but crumbled isolation on a cable where it enters a ballast enclosure. Time to replace the wiring, it probably is crumbling after 20+ years in the Sun light. Alternatively, it was a ballast failure but then it means, that the ballast enclosure on that luminaire was not closed properly, which was the cause of the failure in the first place

If ballasts are getting unreliable, its likely series capacitors (assuming CWA ?) at fault. Test them with a capacitance meter, they will likely show well below their rating which means that they are EOL. Replace them and odds are that everything will work well for many more years


The tripped main will happen even if there are individual fuses or breakers in each luminaire, if there is no coordination between them and the main breaker for the installation. The main breaker should not be just any random MCB of the correct rating, but an MCCB that is matched to work correctly with downstream breakers, so that it will only ever trip when the short happens in the main cables before the downstream breaker