3 ms·

Once upon a time, in the nuclear submarine navy, my shipmate tags out the ship's battery breaker. As part of the tagout, he checks that the ship's DC bus is de

Once upon a time, in the nuclear submarine navy, my shipmate tags out the ship's battery breaker. As part of the tagout, he checks that the ship's DC bus is deenergized - within the battery breaker box itself. During the check, he finds some voltage, which isn't entirely unexpected, since there is enough capacitance on the DC bus to hold it charged for a while. So he uses a specialized grounding probe - about 1/8" diameter copper rod with a reinforced handle - to discharge it. Unfortunately, he has misunderstood what was inside the breaker box and is actually shorting out the ship's main battery! This is a couple hundred volts DC, and a few thousand amp-hours of capacity, and it delivers enough current to instantly vaporized the grounding rod. He's knocked on his ass by the arc blast. Fortunately, he was correctly considering the box to be energized gear and was wearing a full set of PPE, suffering only minor flash damage to his eyes.

jacquesm 11y ago
Lucky guy, lucky too he used a relatively thin rod, a thicker one and it would have been quite a different ending. I did a similarly stupid thing one day. While repairing a clock for a display on a trade show I hooked the ground crocodile clamp of my scope to what I thought was the ground but which in fact was V- of the DC supply voltage of the neon light installation that was use to drive the display. I had a blind spot in the middle of my eyes for many days after that (and took out a fairly large chunk of the mains supply for the Eastern district of Amsterdam). The crocodile clamp totally disappeared, the scope, miraculously survived and wasn't even out of spec. Every time I use a crocodile clamp to hook it on to something I think back to that moment when the clamp makes contact and some part of me expects it to happen again.
- brandmeyer 11y ago
  > I hooked the ground crocodile clamp of my scope to what I thought was the ground but which in fact was V- of the DC supply voltage of the neon light installation that was use to drive the display. Yeao! I own a couple of high-voltage differential probes for this very purpose. Even though most single-ended scope probes are rated to 300V Cat II, I won't go anywhere near main's power with them.
CamperBob2 11y ago
Pretty hard to top that. "I bought some fuming nitric acid on eBay and spilled it on the carpet. Dad was pissed." "I fused two screwdrivers together with a photoflash capacitor. Sears refused to give me a refund." "I accidentally made chloramine gas and experienced short-term breathing difficulties." "Yeah, well, I shorted out a nuclear submarine battery." silence
- jacquesm 11y ago
  No, he did not short out the reactor, he shorted out the battery.
  - CamperBob2 11y ago
    Edited just before you posted that comment, because I somehow knew it was coming. Sigh.

jacquesm 11y ago

Lucky guy, lucky too he used a relatively thin rod, a thicker one and it would have been quite a different ending. I did a similarly stupid thing one day. While repairing a clock for a display on a trade show I hooked the ground crocodile clamp of my scope to what I thought was the ground but which in fact was V- of the DC supply voltage of the neon light installation that was use to drive the display. I had a blind spot in the middle of my eyes for many days after that (and took out a fairly large chunk of the mains supply for the Eastern district of Amsterdam). The crocodile clamp totally disappeared, the scope, miraculously survived and wasn't even out of spec. Every time I use a crocodile clamp to hook it on to something I think back to that moment when the clamp makes contact and some part of me expects it to happen again.

brandmeyer 11y ago
> I hooked the ground crocodile clamp of my scope to what I thought was the ground but which in fact was V- of the DC supply voltage of the neon light installation that was use to drive the display. Yeao! I own a couple of high-voltage differential probes for this very purpose. Even though most single-ended scope probes are rated to 300V Cat II, I won't go anywhere near main's power with them.

CamperBob2 11y ago

Pretty hard to top that. "I bought some fuming nitric acid on eBay and spilled it on the carpet. Dad was pissed." "I fused two screwdrivers together with a photoflash capacitor. Sears refused to give me a refund." "I accidentally made chloramine gas and experienced short-term breathing difficulties." "Yeah, well, I shorted out a nuclear submarine battery." silence

jacquesm 11y ago
No, he did not short out the reactor, he shorted out the battery.
- CamperBob2 11y ago
  Edited just before you posted that comment, because I somehow knew it was coming. Sigh.