Air Terminals verses SPD

[bphgravity]

Here is a nice short article from a respected expert on lightning protection explaining the purpose of air terminals verses surge protection devices:

It has been over 250 years since Benjamin Franklin invented the lightning rod. Buildings did not have electricity, communication systems, or electronic gadgets at that time. Hence neither Franklin rods, nor any other form of protection against the direct lightning strokes to a building, were ever intended to protect the electrical systems, the communication systems, or the electronic equipment within the building. This fact remains valid today, same as it was 250 years ago.

An unprotected building is at risk of lightning-initiated fire. It is also at risk of structural damage which would occur when moisture within a structural component is converted into high pressure steam, which would then cause an explosion. Franklin rods were invented to protect against the above effects. When electrical, electronic and plumbing systems became part of our buildings, they introduced an additional risk of arcing between the down wires and any adjacent metallic component of those systems. In addition to increasing the risk of fire, such arcs could damage those systems or cause shocks to the occupants. Hence Franklin rod systems were modified by adding the requirement of bonding. Nevertheless, the main objective of Franklin systems remains the same: fire and structural protection. That is why the Standard for the Installation of Lightning Protection Systems (NFPA 780) is sponsored by the (US) National Fire Protection Association.

Of course, a direct stroke to a building can damage the electrical systems, the communication systems, and the electrical and electronic devices within it. However, the frequency of direct strikes to a typical building is rather small. On the other hand, the frequency of surges that enter buildings over electrical and communication wires is many times larger than the frequency of direct lightning strokes. Hence surge protection for valuable electronics is highly recommended even if the Lightning Risk Assessment (as per Standard NFPA 780: Appendix H in the 2000 edition, or Appendix L in the 2008 edition) indicates that the building need not be protected against direct lightning strokes.

In summary, Franklin rods do not protect the electrical systems, the communication systems nor the electronic devices within the building. Similarly, surge protection devices do not protect the building against the fire and/or structural damage that would be caused by a direct lightning stroke! Rather, these protection systems serve different functions, and promoting one of them has no implications regarding the need for the other.

Thank you.

Abdul M. Mousa, Ph.D., P. Eng., Fellow IEEE

 

[ron]

They go hand-in-hand.

 

[rick hart]

I do not claim to be an expert on the matter but I think that in order to have a UL label on a Franklin lightning system installation, a SPD must be installed on the service.

 

[bphgravity]

Yes. Surge Protection is a component of the UL Master Label of a certified Lightning Protection System.

I posted this becuase of the most common misconceptions of Lightning Protection that shows up periodically on this and other Forums.

Here in Florida, we have many Lightning Protection Contractors that make false claims on the benefits and protection coverages of the systems they install. Perhaps only 10% of the LPS installed here in Florida are Ul Master Label Certified. Many aren't even inspected by the local building deparmnt...