Electricity Kills

[Clusterfrack]

That's interesting. Despite the movie and TV shows where car batteries and jumper cables are used to inflict torture, I've never heard of anyone actually being shocked by 12V. I can grab hold of both posts of a car or heavy equipment battery and hold on all day without feeling a thing, and some of those are rated in the 1200 or more CCA range. I would guess that many engine starting motors are in the same hp / amperage draw range as the servomotor you're describing.

Were there odd conditions on that job?

Man, I don't know... Might have been 24VDC. High current for sure.

[theJanitor]

Getting hit by a MSD ignition box hurts pretty good. I got hit pretty hard by a 600amp, 220 volt main. Blew me about 7 feet off. That wasn't a fun experience

[farscott]

That's interesting. Despite the movie and TV shows where car batteries and jumper cables are used to inflict torture, I've never heard of anyone actually being shocked by 12V. I can grab hold of both posts of a car or heavy equipment battery and hold on all day without feeling a thing, and some of those are rated in the 1200 or more CCA range. I would guess that many engine starting motors are in the same hp / amperage draw range as the servomotor you're describing.

Were there odd conditions on that job?

It is possible that the 12V supply was not referenced to earth ground but was not floating. For example, I did a lot of power supply designs for inverters where we took 120VAC, rectified it to 170VDC, and then used a voltage doubler to create a 340V bus. That allows the use of smaller current for the same power, meaning lower conduction losses in the drive switches.

Then the microcontroller power supply would be set to 3.3V above the "ground" reference for the inverter. 3.3V is not much until you realize that the reference is now 170V BELOW earth ground as the voltage doubler midpoint is neutral. The designs were frequently around 1 hp (used about 410uF of equivalent capacitance to stabilize the DC bus) so touching that 3.3V rail would provide a nice jolt.

[JohnO]

Do not screw around with electricity. Especially multi-phase sources like 220 VAC and 480 VAC. The potential exists for Arc Flash. The energy released during an Arc Flash is nothing anyone wants to be near without the proper PPE Personal protective Equipment. I have seen the aftermath and it is devastating.

The following video illustrates what can happen and the individuals are not wearing proper PPE.

[Jared]

I've taken two hits from 3 phase 480VAC. It's not fun, especially the one that went hand to hand and I still don't understand how that one happened.

Seriously, like was said above, do not screw around with electricity. I've been working with it for almost 15 years and have been quoted as saying "you'll never find another electrician that has as much respect for electricity as me."

[Wheeler]

I've been hung up on 277VAC, both the hot and the neutral, (at separate times.) It hurts. A lot. Very few folks have actually been hit by 480 as they would have to make contact with two separate current carrying conductors (hot wires,) to actually have 480 V pass through them.

Arc Flash is a real thing. The video above shows an extreme example, it's one of the training videos we have to watch occasionally. It is not nearly as likely to happen in what is considered a low voltage system, typically referred to as 120/208 VAC. It is much more likely in what is referred to as a high voltage system, (277/480VAC.) keep in mind that 220VAC is the typical voltage in domiciles in the USA.

[Wheeler]

I've taken two hits from 3 phase 480VAC. It's not fun, especially the one that went hand to hand and I still don't understand how that one happened.

Seriously, like was said above, do not screw around with electricity. I've been working with it for almost 15 years and have been quoted as saying "you'll never find another electrician that has as much respect for electricity as me."

That shit will put the fear of God in one for sure.

[ranger]

I made the mistake of putting a steel feeler gauge in between the points on an old Mustang with the ignition switch on - maybe it was only 12v but it was all I wanted!

[JAD]

In my new job I play with batteries, sized to propel ferries or source power for directed energy weapons. After years in RF and AC, I have a newfound respect for DC.

[BobM]

Thanks to the OP for bringing this up. The power company used to put on a safety presentation for police, fire, and street dept workers. We've had quite a bit of turnover since we last had them come in. I'm going to see if we can get them to do it again.