- Location
- Massachusetts
But we do know electricity takes all available paths, not just the path of least impedance. With that being the case I do not understand what a rod will really do. A lethal shock level is very low.
Stage grounding/ Generator Grounding
- Thread starter mason.dale
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But we do know electricity takes all available paths, not just the path of least impedance. With that being the case I do not understand what a rod will really do. A lethal shock level is very low.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The problem with lightning, which make it so difficult to calculate and predict just based on our experience is this:
At the high frequencies (and therefore high dV/dt) of the stroke, inductive effects will dominate in the choice among parallel paths. A high inductance bottleneck (like a coiled instead of straight bond wire) can cause a high enough voltage to build up that the electrons will break down a path through the air instead. That path, like the wide ranging arcs that you see even at the low frequencies of substation wiring, can go almost anywhere once they have started, because the ionized air provides a lower reactance (big ionized cylinder = low inductance), it will end up carrying the bulk of the current and that arc can move both its middle and its endpoints in ways that are very hard to predict.
If you are touching metal, no matter how well grounded, then as you say you are genuinely at risk no matter how well the metal is bonded. What you can hope for is to prevent arcs that will hit you even while you stand or sit in the middle of a room.
John120/240
Senior Member
- Location
- Olathe, Kansas
What is the theory behind lighting conductors being flat braided wire vs solid or stranded ? Obviously more surface area. What is the rest of the story ? credit to PH
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The theory is that the flat braided conductor has lower inductance as well as lower resistance related to skin effect.
I think that is a common misconception about strike (stroke?) current. If current were simply DC, yes it has a direction, but irrelevant to the potential for damage or threat to life. The mere mention of current frequency says the current at the very least has an AC component... but that is only relevant to resistance vs. impedance, and still irrelevant to the potential for damage or threat to life... not to mention that the current doesn't just travel to ground (earth) but both directions.
Then I'm in agreement with Bob (iwire). How does earth bonding an above-ground conductive structure change anything? With the ends of the strike being earth and sky, the structure is still there whether earth bonded or not. Unless the structure is actually designed to minimize bizarre pathways, I don't see earth bonding as the sole remedy to mitigate property damage or threat to life... and actually quite the opposite.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
OK. Change "to ground" to "to or from ground", although I did not intend to imply a direction, just an endpoint.
An air terminal (lightning rod tip) with its sharp point, is intended to ionize the air locally to persuade any eventual strike to include the rod in its path.
It can also bleed off the local static charge to some extent without an actual stroke being formed.
An air terminal (lightning rod tip) with its sharp point, is intended to ionize the air locally to persuade any eventual strike to include the rod in its path.
It can also bleed off the local static charge to some extent without an actual stroke being formed.
Curious nerd
Member
- Location
- Washington State, USA
Protecting equipment, people, or both?
Protecting equipment, people, or both?
For equipment protection it's vital to avoid ground loops. If two things are grounded but grounded to different rods, a lightning strike can cause thousands of volts of potential difference between them.
For structure protection, a downlead carries current that would otherwise be trying to melt the structure.
The theory behind earthing is that since the lightning strike will go to ground no matter what, that a low-impedance road for it to do so reduces the amount of damage to all the other things it can go through to reach ground.
The RF components of the strike are better dealt with by a radial system.
See http://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/Single-Point-Ground~20040427.php and anything here by Dr. Mousa.
Protecting equipment, people, or both?
For equipment protection it's vital to avoid ground loops. If two things are grounded but grounded to different rods, a lightning strike can cause thousands of volts of potential difference between them.
For structure protection, a downlead carries current that would otherwise be trying to melt the structure.
The theory behind earthing is that since the lightning strike will go to ground no matter what, that a low-impedance road for it to do so reduces the amount of damage to all the other things it can go through to reach ground.
The RF components of the strike are better dealt with by a radial system.
See http://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/Single-Point-Ground~20040427.php and anything here by Dr. Mousa.
With a lightning rod installed, that implies a designed system to mitigate the threat to property and life. That's like sending out event invitations to more people than you plan to attend, and more people show up than planned.
If you think about it, bleeding off local static charge has both pro and con implications.
While I'll not say lightning protection systems and theories do not have merit, the prevalent factor to implementation is simply that people like to feel safe.
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