Lightning protection - is one of the ways to protect property and health from harmful effects of lightning. Therefore, to ensure comprehensive protection, it is necessary to correctly understand its operation principles, as well as principles of interaction with other devices. Our technicians get many interesting questions on this issue. So this time we would like to share one of them:
Question: Will relay or differential breaker activate at a close thunderstorm before electronics in the house burns?
Answer: If to study a close thunderstorm, then the threat comes from the induced voltages which are described by the pulse of 8/20 ms shape. Front time is 8 ms, SPD with a response time of less than 25 nanoseconds are used to restrict such pulses. Differential breaker or voltage relays, not to mention the fact that they are not intended to limit the lightning current, at best, have a response time of 0.005-0.01 second. It can be seen that the differential breaker does not have time to disconnect and will miss the complete pulse. Even if the differential breaker has a built-in surge protection, more often its characteristics are close to the SPD test class 3, which must be installed after the SPD Class 1 and 2, and serves to protect the sensitive electronics. It is not enough to limit a direct lightning impulse current.
To limit the induced surges that come through, it is necessary to use SPD Class 2, to limit direct lightning current, for example, when external lightning protection is installed on the house - SPD class 1.
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See also:
- Design of grounding and lightning protection
- Webinar series: questions and problems arising in the design
- Interview with the designer of industrial facilities
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