Picture of Power Meter Lightning Strike

[dingdongrb]

Things that make you go hmmmmmmmm:

 

Does lightening go up from the ground into the sky or does it start in the sky and go to the ground?

 

I'm wondering what the odds are of having your meter get hit by a lightening strike?

[sometimewoodworker]

25 minutes ago, dingdongrb said:

Does lightening go up from the ground into the sky or does it start in the sky and go to the ground?

lightning bolts vary from 5 kA to 200 kA and voltages are from 40 kV to 120 kV. Given those potentials virtually nothing you can do makes a huge difference to a direct strike, a near strike kills some cattle due to the voltage difference between legs
 

they can be positive or negative and it is the difference between the ground voltage or earthing potential that causes the strike. 
The answer to your question is that Cloud-to-ground lightning comes from the sky down, but the part you see comes from the ground up and is the brighter flash. However the combination S->G & G->S strike is around 1/1000000 millionth of a second.

 

fortunately the majority of strikes are cloud to cloud

Edited April 12, 2023 by sometimewoodworker

[degrub]

I saw a photograph online recently that showed many upward electrical discharge leaders from structures trying to connect with the discharge coming down from the cloud.  Very cool photo.
 

The air terminals only attempt to guide the high current discharge around the structure. They do appear to have an effect at preventing or reducing damage. 
In Franklin’s day, the fire insurance payouts were reported to have decreased after church steeples were outfitted with earthed air terminals. It may have been just the presence of the earthing wire at the tip of the steeple and not the air terminal itself that made the difference. 
 

In chemical plants and refineries, we go to great efforts to ensure that the steel structures and equipment are adequately bonded to earth through the foundations and through connected earthing rods or grids. This is an attempt to ensure the the ground potential and the potential at the tip of the structure are the same - as if there was no structure there. It also ensures a path to earth that can handle high currents. However, tall structures, poking up into the atmosphere can distort and compress the shape of an electric field forming above the earth due to a storm cloud in the area possibly increasing the chance of a hit. Not that a cloud discharge will hit there every time,  but higher odds though. 
Just look at the lightning protection towers in place around rocket launch facilities in Florida used to reduce the odds of a hit to the rocket.

[carlyai]

13 hours ago, Encid said:

I found this section from degrub's reference article particularly interesting...

 

"Cloud-to-ground lightning strokes initiate high in thunderstorms, miles above the surface where ground objects have no effect. Even after initiation of the discharge, the downward-moving stepped leader is 'blind' to objects on the ground until it is very close to the ground, within 50 to 100 feet. At that distance, lightning will strike within the very small area it is already descending in, regardless of any devices nearby that claim to divert or prevent the strike. For example, a photograph exists of a lightning strike to the Merchandise Mart building in downtown Chicago. Merchandise Mart is very close to the 1,700 foot tall Sears Tower, yet not even the Sears Tower influenced the ground connection of this close cloud-to-ground stroke."

 

As a lightning bolt's ground connection is already 'set in stone', so to speak... nothing short of a large telecoms tower or skyscraper will attract or deflect the bolt away from its target... which is a factor of the position of the storm rather than objects on the ground.

 

I wonder if it's worth it? 

I have seen lightning strike a tree in a gully about 50m away from a 500' geodesic constructed television tower. 

All protection will help but...

Also voltage stabilisers on the incoming mains may also help. 

We had a planned PEA (not sure planed and PEA go together) outage and when they reconnected the power, I think they forgot the neutral. Blew up lots of village TV'S etc. We had a brown smell coming from the stabilisers going into orbit, and soiled underpants but apart from that all OK.

[Crossy]

22 minutes ago, carlyai said:

We had a planned PEA (not sure planed and PEA go together) outage and when they reconnected the power, I think they forgot the neutral. Blew up lots of village TV'S etc.

 

Missing neutral or a phase-neutral swap can get most "interesting". Surge supressors and over/under trips are definitely a wise investment.