lightning damage can be extensive and costly, its even life-threatening.
If I have properly grounded the equipment and have a Surge protection device, do I have to disconnect the antennas during the thunderstorms?
What is "proper" grounding and protection?
In my experience, most amateur stations that have installed grounding and surge protection devices have not installed them properly. Surge protection devices are designed to handle relatively small voltage transients, not handle surge currents on the order of a lightning strike. And with the tremendous currents involved in a strike, even a few milliohms is enough impedance to generate voltages high enough to cause damage. As such, protection efficacy is much more about where and how grounds and protection devices are installed rather than if they are installed at all. See How can I protect equipment against a lightning strike?
It is certainly possible for a well-designed station to reduce the lightning risk below the threshold necessary to justify the hassle of disconnecting the antennas. Consider commercial stations: the antennas are never disconnected. Although they do suffer damage occasionally, most times they are able to continue operating through a thunderstorm without incident.
As far as I know the probability of direct strike to the antenna is considered relatively small. And if it will happen it is unlikely that your antenna will survive anyway (or the protection will cost more than the antenna itself).
Static electricity which is formed in the antenna during storms represents the greater danger to the radio in practice. Although there are various ways to mitigate this danger (bleeder resistors, inductance between the shield and the core of the coax, ...), personally I follow two simple rules:
- Never operate during the storm or if you see the lightning on the horizon.
- When not operating, disconned the antenna from the radio. Then connect the antenna to the 100W dummy load. The dummy load will prevent the static charge to be accumulated in the antenna.
While I completely agree with Phil on everything he wrote, antennas are not the only path to your equipment from a lightning strike.
According to the map of Estimated Effective Ground Conductivity in the United States, I enjoy the privilege of living in a rural area with 0.5mS/m of ground conductivity - the lowest value on the map. Low conductivity means large voltages induced in the Earth by lightning strikes.
I note the rural location because the telephone and electrical utilities "sometimes" don't invest what they should to maintain the grounding integrity of their systems. Result: hundreds of dollars of losses of electrical and electronic equipment and appliances connected to the AC mains and/or to the phone lines.
And, don't forget your rotor cable - another good pickup for the strong electric fields induced by nearby lightning strikes!
I disconnect EVERYTHING when not in use and haven't had a loss since I instituted this policy, despite some frighteningly close strikes.