On Sat, Nov 16, 2024 at 05:10 PM, Glenn Little wrote:
How do you prevent damage from a lightning event if everything is not
referenced to one ground (earthing point)?
The potential difference between the two, or more, earth points can be very
substantial.
This potential difference is what causes the damage.
Glenn
A single "ground" makes little or no difference. You need all aerials and power cables, Cable TV, phone cables disconnected. A strike even 100m from the utility cables (even buried electricity, phone, cable TV etc) can induce 1000s of volts and destroy front ends of TV, radio, DSL modem, cable modem, analogue dial up modem. Even blow the tops of the RS232 interface ICs on the motherboard (amazingly a plug-in RS232 card and new modem worked once they repaired the exchange, the Mobo survived).
There are reasons for a single electrical safety earth do to with ELCB / RLCB / RCCB tripping and safety. As mentioned, the UK mostly is a different scheme (3rd wire with earth to substation) to Ireland (an earth spike per meter box and no 3rd wire). Unlike USA, UK & Ireland homes are only single phase. The houses alternately use the three phases in built up areas, so don't share any electrical device connection with a neighbour without suitable isolation or barrier earth (shared TV aerials or sat dishes).
Radio earth connections want to be short to earth spike so there may be more than one.
Solar systems on a roof need the frames to a single earth to minimise static damage, useless on a direct or close strike. The battery negative should not be earthed except in certain circumstances. The neutral on an off grid PV inverter needs a single earth before the trip switch. Earthing (other than the isolated metal frames) of PV systems connected to a grid need an expert.
A Satellite dish or Aerial pole should go to a local earth spike to minimise static (dry wind) or damage from nearer but not direct hit lightning. The satellite dish electronics (ODU, LNB etc) should not be directly earthed.
It's complicated. But a single earth doesn't help with lightning. Disconnecting everything works best, but not fool proof if you get a direct hit.
See also EMP.
Mike EI9FEB