EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: giovimonto on January 26, 2016, 05:26:21 pm
-
Why there is a 1M? resistor in an anti-static wristband?
Shouldn't the current be able to quickly leave my body?
-
Zaps are unpleasant, dissipating it more slowly is preferred.
Besides, it is just there to stop the static building up, not dumping a potential out of nowhere
And it's handy to be able to measure a defined value when testing to see if the strap is still functional
-
More to the point, its there for your safety. Shock currents in excess of 10mA through the skin are generally regarded as hazardous. Assuming you aren't working on anything above 360V (the bus voltage in a EU SMPSU under high mains conditions), the 1Meg resistor will limit the current to 0.36mA, which is extremely unlikely to cause any injury.
-
^
Isn't that assuming the person isn't earthed by some other route?
I'd assume the bench RCB would deal with any ground current issue, but yeh, fair point.
-
If you are earthed by another route, the wrist strap manufacturer isn't liable
-
It is not only there for your safety, it is absolutely essential to the operation of the wristband. The term ESD exists for a reason. Electrostatic discharge - it's not the voltage/charge that's a problem, it's the current that flows when you discharge it. If you were solidly grounded, and touched a part that had picked up charge, you'd discharge it very quickly and kill it.
-
I beg to differ slightly. Due to the human body's capacitance to ground, you can still kill a highly charged, very ESD sensitive device just by touching it, even with a 1Meg resistor in your wrist strap. It does however decrease the risk for less sensitive devices.
-
Well, yes, I never said it was perfect...
-
I prefer applying ESD as if I were doing an EKG........ :-DD