6

Is grounding oneself using anti-static wrist band (connected to ground wire & having a protective resistor) still dangerous in case a very high current flows through the ground wire (due to some short-circuit/ faulty lines)?

Will the power rating of the resistor (generally 1 Mega ohm 1/2 Watt resistor used) be sufficient in case a very large current surges through the ground wire & a person is grounded with it (via anti-static wrist band)? Or do we need to use a higher Watt resistor (power rating > 1/2 Watt) to take care of this particular situation?

Improve this question
7
  • The last thing you want if you accidentally touch a hot chassis is for your body to be grounded.
    – Fiasco Labs
    Aug 5, 2012 at 7:13
  • Also, to the OP, you should unplug your devices when you're working on them unless it's like a hotswap drive or something.
    – cutrightjm
    Aug 5, 2012 at 7:18
  • @ekaj Yep, when you become the ground circuit and the current path through your chest causes fibrillation, you become a statistic. Or did you not know that?
    – Fiasco Labs
    Aug 5, 2012 at 7:24
  • If you're worried about getting shocked, you actually want to do the opposite and insulate yourself from any potential grounds. The idea is to become the path of most resistance for any current to take. DO NOT GROUND YOURSELF if you will potentially be coming in contact with live electronics. That's a good way to suffer shocks, electrical burns, and heart failure.
    – Joel Cornett
    Aug 5, 2012 at 14:09
  • 1
    @Joel Cornett - It's why all the electricians I know favor fiberglass ladders. There are times when you will be working on live circuits (ballast changeouts in production plants for example), plus the healthy assumption that all circuits are live until proved otherwise.
    – Fiasco Labs
    Aug 5, 2012 at 15:32

3 Answers 3

Reset to default
11

Think this out a little bit. The wrist strap is there to tap off static you've built up through your clothing, shoe interaction with carpet, etc.

In a scenario where you grab hold of a 220V cable and are safely grounded through nothing but that wrist strap, if we were to assume that your body magically had zero resistance, then 0.00022 Amp would flow through that 1M Ohm resistor to ground (i=E/r or 220V/1,000,000 Ohms) saving you from heart fibrillation. It is of high resistance because that prevents you from seeing a high current flow at lines voltage but presents a ready path to ground for static.

That 1M Ohm resistor would be dissipating 0.0484 Watt if it were to bridge a 220 mains by itself (P=E*i or 0.00022A*220V), so the day one burns out is the day that Ohm's law has collapsed into the dust or that you were really unlucky and met up with something in the kV range.

Moral of the story, Wrist straps are there to prevent you from zapping silicon. System grounds are there to protect you from having hot chassis conditions that cause you to become the ground circuit. Shields, covers and interlocks are there to prevent you from sticking your hands into mains voltages which could zap you and kill you if your wrist strap was some piece of cheap junk that didn't have a proper high resistance, low wattage resistor in it.

One of our avionics shop routines is to check all new wrist straps for proper resistance (quality check that they're made properly) and all used ones to make sure the conductor path didn't break.

Improve this answer
7

An anti-static wristband is meant to protect electronic components from being damaged by static electricity from your body. Ever shuffle your feet across a carpet and then "zap" the next person you touch? That amount of current is harmless to a human, but potentially damaging to electronic parts, so the wristband prevents that.

It's not meant to protect you from being shocked by your electronics. If you're concerned about faulty wiring causing "very large current surges", you need to consult a qualified electrician. Don't rely on an anti-static wristband to protect you from harm.

Improve this answer
2
  • 1
    actually, if you can feel that "little" zap, it can and will destroy processors, ram, motherboards, and hard drives. Its not potentially, it is. :)
    – Wolfizen
    Aug 5, 2012 at 7:01
  • It is "potentially". I've seen processors surviving a visible zap. Maybe unlikely, but can happen.
    – vsz
    Aug 5, 2012 at 11:51
-1

A "ground" is, generally speaking, where you want the electricity to go. Otherwise (and I'm grossly oversimplifying) it basically goes "everywhere".

If you wear a grounding strap, virtually all of the electricity goes into YOU. Which, when you're working with the extremely low amounts of electricity generated by static whilst you're working on a computer, is less harmful to you than it is to the components you're messing with (you literally won't even feel it most of the time, it can fry unprotected electronics).

However, in a situation where you're working with more power (something plugged into a wall, or even the unshielded capacitors inside a computer's power supply - which is why you're NEVER supposed to open them up), all that electricity going into YOU is a major problem - one that usually leads to a charbroiled technician.

So in a nutshell: DO use grounding straps in situations where the voltages/amps are very low and dangers of shock are more concern to the machine than you. Know that you WILL take all the shocks.

DON'T use a grounding strap in situations where your body can't take the potential shock.

When in doubt, don't use a strap. Accidentally frying a component inside the computer isn't nearly as bad (or as expensive) as accidentally frying the technician.

Improve this answer
1
  • The OP is referring to ESD prevention, not grounding in the sense of low-resistance grounding straps.
    – Andrew Morton
    Jan 16, 2021 at 14:02

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .