Blew a transformer in a crawlspace in St. Louis last Thursday

I was running a new coax line in this old building downtown and accidentally nicked a live wire with my drill bit. The whole block went dark for about 15 minutes, had to wait for the power company to show up and reset it before I could finish the job. Anyone else ever hit something they shouldn't have in a tight space?

2 comments

2 Comments

the_willow20h ago

That coax line couldn't have blown a transformer though. Coax is low voltage, maybe 10-30 volts max off the line, not enough to short anything at 13,800 volts on the primary side. You probably hit the neutral or a phase conductor feeding the building's panel, which tripped the main breaker or blew a fuse on the utility side, not the actual transformer. Transformers don't normally blow from a drill nick, they'd need a direct dead short on the secondary side like two hots touching. Power company probably just had to reset a recloser or swap a fuse at the padmount, not actually repair the transformer.

evan_harris1419h ago

Yeah I was reading the other day that most "blown transformers" in residential or light commercial are actually just blown fuses or tripped reclosers, not the transformer itself dying. Makes sense with what you're saying about the drill nick being too small to take out a proper transformer.