I wanted to make sure my ESD wrist-strap is in working order. So I tested like this:
- Connected the wrist-strap to household ground (via wall socket).
- Measured the resistance between the wrist-strap and the exposed ground of my PC's front USB port (using a non-name brand digital multimeter).
The test worked fine but I realised that the PC was powered on. I've always been told not to measure resistance on a powered circuit because the multimeter applies a voltage to do its measurement.
So, doing what I just did, any chance of damage to the USB port/controller/PC? I don't know enough about electronics to figure this out, though my gut instinct is that tickling ground in the way I did shouldn't matter at all. Still, a definitive answer would be nice!
Best Answer
The reason not to measure resistance on a powered circuit has more to do with possibly damaging the multimeter because of voltages that are applied from the outside. Because of the way ohmmeters work (they must pass a current through the circuit being measured, so their internal resistance can't be arbitrarily high) it's more difficult to protect them from externally applied voltage.
If the wall sockets are wired properly there's no risk of any damage doing this, but there is an outside chance you might not get an accurate reading because there might be a small voltage present between the two grounds due to some leakage somewhere in your house electrical system.
Why would you not just measure between the ground connection and the strap?