Grounded outlet

[Mark Lloyd]

In that picture, his right hand is likely to be wet, increasing conductivity.

[Mark Lloyd]

I used to know a person who claimed that no one knew what electricity is.

[w_tom]

Ground for static electricity is not same ground for lightning. Conductive paint inside a computer's plastic case connected to floor - a ground for static electricity - would mean that electrical current does not flow destructively through electronics.

Lightning needs a different ground - earth. Wire is not a perfect conductor. For example, a wall receptacle safety ground may measure less than 0.2 ohms resistance to the earth ground rod. But same 50 foot wire connected to breaker box might be 130 ohms impedance. Electrical characteristics of that transient are important. A trivial

100 amp lightning transient might see (less than) 12000 volts between wall receptacle and breaker box. Where is the protection? 12,000 volts would then find other (and destructive) paths to earth because it was permitted near to electronics. Again, the word for this transient is 'impedance' - and why lightning must be earthed where it enters a building.

Grounding for lightning is where utility wires enter a building. Effective lightning protectors ground to earth. Grounding for static electricity means an electrical connection from hand to floor and shoes that does not pass through electronics. That ground is somewhere in that 'hand to floor' circuit.

Electrical switch specifications often claim protection from up to

20,000 volts. That means no static electricity passes from hand into switch electrical contacts. What is not always obvious? That 20,000 volt protection does not exist if the switch body is not properly connected to chassis ground. Again, what is the discharge path? If electricity comes out of finger, then what is other side of that 'battery' or 'charged capacitor' that is being discharged? Only relevant ground is a point in that circuit. For static electricity, earth ground is not part of the circuit - not relevant.

For different types of destructive transients, first define the complete electrical circuit. Only then is one point is that circuit called 'ground'.

[Bud--]

The IEEE guide to surges and protection at:

plug-in suppressors as clamping the voltage on all wires (signal and power) to the common ground at the suppressor. Earthing is not the primary mode of protection.

-- bud--