Wouldn't it be more effective for ground wrist straps to not have the resistance in series to ground?

 

The problem with that is the peak current through the ground strap can be higher, making it more likely that the discharge could damage something.

Also, the resistor protects the operator from electrocution should she or he come in contact with high voltage -image working on a production line, adjusting an appliance and accidentally touching the AC line while your other wrist is solidly wired to earth?

 

Current from a charged item though a poorly protected input or output connection.

 

Dick is correct. Sudden discharge can damage components. That's why you want a slower discharge, so that something charged that you approach, you don't present a ripe target for static to fly through your component to ground. The resistor prevents that.

Dick also mentioned the danger of being solidly grounded. Suppose your right wrist is grounded through no resistance and your left hand accidentally touches a live line. We're no longer talking about static discharge, we're talking about discharging your life force. Death in other words.

Just to be clear, I was messing with an amplifier. As we all sometimes do - I forgot to unplug it. Touched mains with my right hand while my right arm was resting on the case. Learned a quick and unpleasant reminder of the need to disconnect from power before working on equipment. My ground strap is on my left, so my left hand is the side often grounded. Had I touched mains and NOT the chassis, and had been grounded directly to ground I might not be here to tell you about my foolish mistake. A mistake that could have cost my life.

The two reasons stated are exactly the reasons why you use a high ohm resistance. The standard on setting up ESD safe work environments - if I'm right, formerly specified a 1 meg ohm resistor on the wrist strap. I'm not sure but I think I recently read the resistance has been revised up. Possibly 2 meg ohm, possibly as much as 10 meg ohm. The ESD standard is one I rarely work with, so my familiarity with it is not boast-worthy. Still, the two stated reasons - safe discharge of static AND keeping the operator safe from harm are the #1 and #2 reasons why you use resistance.

 

A wrist strap I see as having a 1 Meg resistor to ground. This serves a few purposes, it allows high voltage static charges to leak through to ground and it also is a safety measure for the wearer. It helps eliminate a shock hazard.

Ron

 

Wouldn't it be more effective for ground wrist straps to not have the resistance in series to ground?

Not really; they're quite effective as they are, with the resistance.

That way the static voltage would be discharge to ground more rapidly.

Strictly speaking that's true, but the difference in discharge rate would be insignificant.

A human body has a capacitance to its surroundings of roughly 100 picofarads. The time constant of a 100 pF capacitor and a 1 MΩ resistor (a value commonly used in anti-static ground straps) is one-tenth of a millisecond, and after just a millisecond (ten time constants) any electrostatic potential on the human body will be reduced by more than 20000:1.

So even with a 1 MΩ resistor in the ground strap, a person's static charge will be dissipated in barely a thousandth of a second.

 

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Only with an ionized blower above your head you can be neutralized, but not as quickly and efficiently as with a wrist strap. With a cord ofcourse