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I know of one instance last year where six or seven terraced shops were subject to damage from a single strike, and not necessarily positive. Every kind of conductive wire was affected regardless of phone/mains. It just goes to show that you should disconnect everything in the event of a nearby storm, but I wouldn't say it was because of a stepped potential ground effect, more likely the arbitrary nature of path potential through available leads (if it was step potential then living organisms would've been affected too).
Lightning Zapped My PC
#22
- Group: Members
- Posts: 3253
- Joined: 22-October 06
- LocationRuncorn
Posted 15 April 2012 - 11:20
Please bear with me because after my stroke I am trying to write something passable with a moron's grip of vocabulary and grammar - my science is intact but I can't fully access it.
When a strike hits the ground, a large pulse of current radiates from the point of strike and assuming the ground is of uniform resistivity the pulse will disperse according to the inverse square rule. In practice the current will take the easiest path and will be mostly confined to areas of low resistivity.
I learned my electronics and physics in a era which wasn't dominated by fragile semiconductor devices. Modern large-scale integrated circuits use MOSFET structures - the insulated gates of individual FETs can be punctured by as little 60 volts. Merely a handling MOSFET device exposes the device to an electrostatic charge of typically 4kV assuming dry air. The area of each MOSFET gate is in the nanometre range and an equally tiny electrostatic charge is enough to destroy the device.
Some very critical electronic systems communicate with the outside world via an EMP (and lightning) proof firewall formed of thermionic valves. Valves are almost completely immune to EMP. Strangley enough, old kit using the first germanium transistors was (and still is) more tolerant of high energy spikes than silicon parts. Likewise, vintage radios and TV sets had valved front ends that easily shrugged off anything less than a immediate strike.
Again telephones were pretty immune to lightning. Telephone exchanges in my day were electromechanical (mostly Strowger but some oddball systems like Rotary). While the General Post Office (GPO) had full control over everything up to the telephone, lines were less vulnerable to lightning damage, and substantial gas-gap suppressors could shunt a lot of the energy of a nearby strike to ground - they looked like large neon bulbs. Nowadays we seem to rely on varistors in the master socket (more bloody semiconductors) which are about as useful as a chocolate teapot.
Sorry - but the Scrabble box in my head has run out of words. Unfortunately I tire very quickly.
Pete
When a strike hits the ground, a large pulse of current radiates from the point of strike and assuming the ground is of uniform resistivity the pulse will disperse according to the inverse square rule. In practice the current will take the easiest path and will be mostly confined to areas of low resistivity.
I learned my electronics and physics in a era which wasn't dominated by fragile semiconductor devices. Modern large-scale integrated circuits use MOSFET structures - the insulated gates of individual FETs can be punctured by as little 60 volts. Merely a handling MOSFET device exposes the device to an electrostatic charge of typically 4kV assuming dry air. The area of each MOSFET gate is in the nanometre range and an equally tiny electrostatic charge is enough to destroy the device.
Some very critical electronic systems communicate with the outside world via an EMP (and lightning) proof firewall formed of thermionic valves. Valves are almost completely immune to EMP. Strangley enough, old kit using the first germanium transistors was (and still is) more tolerant of high energy spikes than silicon parts. Likewise, vintage radios and TV sets had valved front ends that easily shrugged off anything less than a immediate strike.
Again telephones were pretty immune to lightning. Telephone exchanges in my day were electromechanical (mostly Strowger but some oddball systems like Rotary). While the General Post Office (GPO) had full control over everything up to the telephone, lines were less vulnerable to lightning damage, and substantial gas-gap suppressors could shunt a lot of the energy of a nearby strike to ground - they looked like large neon bulbs. Nowadays we seem to rely on varistors in the master socket (more bloody semiconductors) which are about as useful as a chocolate teapot.
Sorry - but the Scrabble box in my head has run out of words. Unfortunately I tire very quickly.
Pete
