I am a bit confused as to why you want a low impedance ground ring attached to all metal parts throughout an industrial plant. Specifically, let's say you have a lightning strike which is upwards to 1,000,000 volts. I understand that I= E/R so wouldn't this mean (though all bonded together so potential should be low) that if something was struck the current (I) would be an astronomical number given a low resistance system so wouldn't that make it very deadly or what am I missing here?
What is Purpose of Low Resistance Grounding System?
- Thread starter kjroller
- Start date
I may have made a mistake the ground ring doesnt mean the rest of the metal parts are at low impedance and it wont protect you from a lighting strike but it will disperse energy like a bleed off valve and the best way is through the low impedance ground rod.
D. Castor
Member
- Location
- Port Angeles, Wash
- Occupation
- Electrical Engineer
Neutral grounding doesn't have much to do with lightning protection. The issue is providing a relatively stable neutral point while limiting equipment damage caused by ground faults. The resistor reduces the maximum possible ground fault current while limiting the possible overvoltages that can occur for ungrounded systems. Low resistance grounding is only used on medum-voltage systems, never on low voltage.
The grounding resistor won't provide protection for damage due to lightning.
The grounding resistor won't provide protection for damage due to lightning.
- Location
- Illinois
- Occupation
- retired electrician
I think he is talking about a solidly grounded system and not a resistance grounded system.
yes I am I get how the neutral works wondering about ground rods/rings specificly
- Location
- Illinois
- Occupation
- retired electrician
Just a connection to earth that plays a very small part in electrical safety. See 250.4(A)(1) for the purpose of connecting an electrical system to earth.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
A low impedance connection to Earth for grounded system is not necessary or safer. Of course there is a powerful faction of the electrical community that believes it is. I am still waiting for the science and electrical theory to back that assertion up.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
There are lots of details to lightning, and this is only a small part of the answer:
You are neglecting the source impedance when you say 1000000 volts and I=E/R. You have "resistance" in the rest of the circuit as well, so even if the resistance of your grounding system is very low, the current in the strike is limited, of course to an extremely high value.
The source voltage and impedance are so high that you are better off approximating the strike as a current source, that many thousands of amps will flow for a brief time through whatever resistance you care to offer, and the voltage is high enough to break down any insulation you offer to prevent that current flow