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Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
I have heard repeatedly that for added protection against electrocution, it is best to make sure any large (high energy) capacitor bank is grounded. Won't this put the user, who is standing on the ground, in greater danger of having the (grounded) capacitor bank discharge through his body to earth if he comes in contact with it? For example, if the "-" lead of a capacitor is 'earthed' then all the 'earthed' user has to do to form a closed circuit through his body and the cap is touch the cap's "+" lead. If the capacitor is UN-grounded, then there is no direct path to ground through a person via either the "+" OR "-" terminals. Also, concerning grounding the case of a metal capacitor: shouldn't this also be risky since there may not be sufficient electrical isolation between the case and either terminal?
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
The more or less obvious thing you're missing is that, for potentials above 1000v ish, you can consider a person grounded for arc to ground safety purposes, whether they appear to be or not. Only the most excessive and scrupulous use of rubber boots and a hazard free workspace could ensure a person stays floating, it simply isn't worth it for the amateur. Below 1000v, the meanest thickness of shirt will probably protect you. Much above 1000v, and electricity will jump and crawl distances and routes you didn't expect, especially if surface contamination is present.
The class book I read at school when I was 12 or so involved a lone cap'n and his cabin boy facing pirates invading the ship. They holed up in a cabin, but opened the door. The reason being that 'at least I will know where my enemies are coming from!'
If you ground one terminal of your cap bank, at least you know the potential of the various terminals, rather than being lulled into a vague and wholey false sense of safety based on things being floating. Try to float the cap, one breakdown of insulation and the other terminal could change in potential by lots, in a short space of time. A solid ground reduces the hazard to you should that happen.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
In principle, there is no great problem in touching one of the terminals of a charged insulated capacitor. You receive just the discharge of part of it's body capacitance. But the insulation must be good enough, as the other terminal rises to the full voltage on the capacitor and may arc to grounded structures nearby, closing the circuit. Every area, if touched, may give a small shock. I like the analog of the pirates. It's best to know exactly where the danger is.
Registered Member #54441
Joined: Mon Feb 09 2015, 11:33AM
Location:
Posts: 9
personal experiance share, when in doubt, always keep one hand in your pocket. that way any current/voltage is not going through your heart between your hands/arms. you would get a shock but not death. also a bleeder resistor is your friend. i always discharge large caps when working on circuits with a bleeder resistor to ground.
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Is it safer --or very dangerous-- to ground your high voltage energy capacitor bank?
