For a couple years now, I have been replacing DVR cards in a PC from lightning hits. The cameras are outside grounded in the open area on the building and I have lightning rods install by a professional.
Why are the cameras grounded? That's dumb. When there is lightning activity, the ground potentials change and there will be huge currents flowing down your wires. The lightning doesn't have to strike your camera or strike at all, merely the potential gradient over the ground between the wires can destroy your devices.
If the camera was electrically isolated from the DVR, then you could ground it; I would only do it for noise reasons (which are likely not existant) and not for lightning immunity. So I wouldn't ground them.
I have a large antenna on the property next door that is probably bring all the lightning to me to make things worse.
Oh, boo. Not everything can be blamed on the neighbours, annoying as they may be. Anyway, that's something you can't change.
It seems it is hitting the cameras (last thing that is recorded is a bright flash on one of the cameras) and the EM spike travels through the coax to the DVR card (PC and its power supply never been replaced AND 12 volt DC PS to the cameras never a problem).
Unlikely the lightning is specifically picking out your cameras unless they're on big poles.
I noticed the ports on the DVR card that are BNC to cat 5 via transformers and back to BNC at the DVR seem to survive, but looking at a resonable cost fiber solution.
Isolation is the normal way to protect from ground pot. shift.
As an example, I know a fellow that had to provide alternate RS422/485 communications between highway signage as the interfaces kept failing in bad weather. He replaced the interfaces with isolated versions (<3kV) and the devices hadn't failed since.
As another example, airport aerodromes, afaik, use underground grounding mesh/cable to reduce the ground impedance and therefore potential difference.
Have a look for 75ohm (or 50ohm, whatever you are using) isolation transformers. Or use back-to-back 75-300 <==> 300-75ohm adapters. Or make your own. Depends on cost, I guess. Some examples:
**broken link removed**
**broken link removed**
You want to increase your isolation voltage rating to as high as possible.
I think the DVR card is a little weak in design and thought if I go to fiber (2 feet of it just before the DVR with a BNC-BNC coupler) it would just be a bright flash light in the fiber and no ground involved.
Fibre has the best isolation, but is expensive.