Understanding Surge Protector Specs for the Computer Age

[kiki_danc]

It is the job of the grounding at the pole and service entrance to prevent that.

However lightning can do exactly what you describe. Happened to me once.
It's good practice to stay away from metal appliances when there's lightning in the neighborhood.

You will find this thread helpful.
https://www.physicsforums.com/threads/not-fully-understanding-grounds.622107/#post-4007190
See post #10.

Ok. I guess putting surge protectors between neutral and ground can minimize the shock(?) maybe that's why there is N-G (Neutral-Ground) protection mode besides L-N, L-G, N-G? Is this the purpose of the N-G mode? When you use the say Siemens 140,000A surge protector and a lightning with energy of 6000V, 130,000A hit the lines.. then the Siemens will absorb them leaving only the VPR of 600 volts?
Tom wrote earlier that
"Consider a nearby lightning strike that puts 6000V on the power line to ground. Much equipment is rated perhaps 600V or so from line to chassis, the the chassis is now at 6000V, and so is everything in it and connected to it. Is there anything near enough to the equipment that a 6000V spark can jump to? For instance the insulation in a transformer would likely break down if anything on its secondary is grounded or near a ground or a large conducting surface. If the transformer is mounted in an electrical box, the box would likely be grounded and the an arc would jump to the transformer core, to the box, to ground. If a person happens to be in contact with the equipment, he/she is now at 6000V; is the floor wet, person touching another piece of equipment at the same time?"

Anyway. I got so much information now that the most logical thing left is to start grounding all metal enclosure and know what surge protectors to use. I guess this is it. Thanks to all who supplied much useful and helpful information!

 

[jim hardy]

If a person happens to be in contact with the equipment, he/she is now at 6000V; is the floor wet, person touching another piece of equipment at the same time?"

Read in one of those links i posted my anecdote about holding a metal cased electric drill when lightning struck my power pole .
I learned most of what i understand about grounding in that visceral half second . I knew the instant it hit exactly what had happened.

So you use multiple protections wherever they're appropriate
grounding to limit voltage between people and earth
and double insulate to prevent current flow through people.In your above scenario ,
if lightning elevated local Earth to 6000 volts so the floor is also at 6000 volts then there's no potential difference to drive current through the person. That's why metal buildings are grounded .

You now have understanding of the principles of grounding
it will take you months to work out in your mind "what if" thought experiments that resolve apparent logical conflicts.
Kirchoff's laws of voltage and current are the thought tools.

have fun ,
and share your knowledge&experience with others as it grows..

 

[berkeman]

Thread is closed for a bit...

 

[Mark44]

The OP's question has been abundantly answered, so I'm closing this thread.