Vertical Conduit Runs

[BryanKScarborough]

I was participating in a design meeting with several engineers (electrical and mechanical) and it was mentioned "Interior" vertical conduits (This building peak is 250' above grade) should be protected with surge arrestors. The conversation was regarding Building Automation circuits and communications.

The explanation I received seemed to be a bit vague and wanted to see if anyone out here was familiar with this and what transient voltages are derived from a vertical conduit?

This could be just a requirement of this project and there is no real issue substance - thought I would inquire anyway.

Thank you in advance,

 

[ron]

Lightning discharge likely has some radius that it effects the building in way and thus the interior conduit, but it would seem that properly designed NFPA 780 Franklin style lightning air terminals on the roof and the associated down conductors would provide sufficient path to ground that the discharge would bypass going inside the building.
Conduit has sufficient bonding in the building for ground fault paths, so if you reinforce that with a wire type EGC and provide surge protection, you are probably in good shape.

 

[Julius Right]

IEC 62305 [IEC standard for lightning protection similar to NFPA 780]

IEC 62305-4 [Annex C] Protection against lightning recommends use of surge protection device on down run conduit