Question on Grounding

[Sarika]

Hi all,
I have watched Mike's video on fundamentals of grounding and was confused in few areas.

He was talking about bigger equipment like CNC machines or generators will not need a ground rod to protect them from lightning, and lightning can actually cause potential difference at the ground rod, which can make lightning pass through the machine and ruin the machine electronics. This is understandable.

But won't indirect lighting cause pressure on electrons in metallic parts of these kind of bigger equipment? Won't this create over voltage in these bigger machines? Then won't we need 'metal' equipment grounding in this case?

Also he was teaching about equipment grounding and we provide grounding to metal part of equipment to reduce over voltage induced due to lightning or any other over voltage sources. But, in this case won't the indirect lightning cause potential difference at the ground rod? And won't this lead lightning to pass through the metal parts of the equipment? How is grounding helping to make the equipment safe in this case?

Please help when you get a chance.

Thank you for your time.

 

[jaggedben]

Hi all,
...

But won't indirect lighting cause pressure on electrons in metallic parts of these kind of bigger equipment?

'Pressure'? What exact physical phenomenon are you referring to and why do you think this is?

I think that it's possible that lightning could create an electromagnetic field in the vicinity of equipment that can induce a field in the equipment itself, but that is not necessarily enough to harm the equipment or be a problem.

Won't this create over voltage in these bigger machines?

Again, why do you think so? (And why do you think the size of the machine makes any difference?) I think the answer is usually that it will not create a high voltage in the machine if the machine does not become part of the direct paths by which the lightning charge dissipates.

Then won't we need 'metal' equipment grounding in this case?

Also he was teaching about equipment grounding and we provide grounding to metal part of equipment to reduce over voltage induced due to lightning or any other over voltage sources. But, in this case won't the indirect lightning cause potential difference at the ground rod? And won't this lead lightning to pass through the metal parts of the equipment? How is grounding helping to make the equipment safe in this case?

Please help when you get a chance.

Thank you for your time.

I don't know which video you watched, but one of the points he has made is that redundant grounding electrodes at equipment provides paths that may encourage lightning to travel through equipment and back to other grounding electrodes on the premises. This is not what you want. Generally you want everything to be grounded, yes. But ideally you want everything to be grounded through one place at the building. Equipment should have a grounding conductor that goes back to this location. Having additional ground rods at each piece of equipment does not necessarily help and may provide unwanted paths for nearby lightning discharge.

I hope that helps.