Local grocery store has 4 wall packs(250Watt,110Volt,Type M58? lamp said multi vapor-wholesale gave merc vapor)) about 12-15 years old.
I replaced lamps in 3 of the 4 and had one arch and spark(caught fire) as I was opening lid, it was getting dark and photos energized while I was moving from fixture to fixture with my extension ladder, luckily the breaker tripped and I removed fixture from wall. The other three appeared in rough shape and I recommended replacing all or perhaps ballasts(not sure if it would save $$ with labor). The manager wants to wait until quarters end...bonus.

My question is why did one lamp burn out within 20 min. of being on?

Does that mean ballast is definitely bad?

The reason for the arching was insulation was melted off conductors, assume ballast is/was overheating. The other 3 showed signs of the same, but not to the extreme.

Thoughts appreciated,
H20

The M-58 is indeed a legit Metal Halide and it is 250 watter.

If you see the " H " lettering that is old mercury vapour that is pretty much history like dino.

The Metal Halide bulbs typically run little hotter than mercury vapour is and they are pretty senstive to burning postion as well espcally with hortzotal verison.

If alot of stuff look pretty much burnted or about ready to become FUBAR it is good time to ditch it and get new one.

15-20 years is not too bad but little short side on lifewise if properly maintened it should last at least 25 years before something major screw up.

The other thing I am not sure but if you can read the ballast info you should able tell if that wallpack have proper bulb in there with med et larger wallpack it common to see 250 and 400 watter in the same housing.

some case I know someone stick in 250 watter in the 400 watt ballast that can overdrive the lamp and really shorten the life and some case it can exploded.{ for sure you will heat up the whole thing pretty easy }

Merci,Marc

Marc raises a good point: it's very easy for someone to put the wrong bulb in these fixtures.

The result? damaged fixtures.

DON'T assume the right bulb is in the fixture. LOOK at the ballast and the fixyure; both should be identified as to what goes in.

OK, they make it confusing. Rather than say "250w MH", they say something like "M58." Still, you ought to be able to find a cross-reference ... for example, google "M58" and you'll find a description.

H2O:
From experience, 12-15 yr old wallpacks are great candidates for replacement. factor in the costs of bulbs, ballasts & labor, against the cost of a new fixture and labor.

You can order new fixtures (with lamps) direct from mfg like RUUD Ltg., or any of the other direct to contractor sellers. The MV bulbs are going to be 'unavailable' by Federal law either very soon, or possibly already. Pulse start MH provide equal light output at reduced input wattage, and new tech induction is a really great energy saver with incredable lamp life, but at a high $$$$ now.