Lightning Protection for Audio Systems

/by
by Wayne Lee

Lightning strikes has destroyed a lot of audio equipment. In this article, Wayne Lee addresses some lightning protection solutions.

Back in 2008-2009 I helped the University of the South with lightning problems at their Chapel high atop the Cumberland Plateau in Sewanee, TN.

There was some SAC discussion back then including recommendations for lighting protection consultants.  They had five large and $$ Intellivox programmable line arrays and had replaced the DSP boards and a few amps more than once, due to lightning strikes.  This narrative was put together with the help of SAC members, my research and conversations with other professionals. I hope it helps.

The Steps

Here is what I have.  It takes a multi-layered approach starting from the entrance to the building and ending at the power outlet or circuit breaker. My initial recommendations are based on conversation with colleagues, some of my design experience and reference materials, but not direct field experience.

Kind of a do it yourself approach:

This will require a licensed Electrician.  I can assist in selecting the devices mentioned below and inspection.  This may be the least expensive approach but maybe not the absolutely BEST approach.

  • 1.    Place a Surge-X PF420 (4-circuit NEMA Box), and/or an SX20NE (1-circuit NEMA Box) AC Power Surge Eliminators on each sound system circuit at the panelboard.  Which ones to use only depends on the number of circuits used here.  This would help the AC Power lines in the building.http://www.surgex.com/
  • 2.    Inspect the grounding system for methods to “arrest” the lightning before it enters the building.  Inspect all grounding systems used in the building for integrity.  I would make sure that you have a good low impedance building ground and that will be at the electrical power entrance of the building.
  • 3.    Maybe even, inspect nearby power lines and systems for protection. This apparently helps avoid strikes in the area.
  • 4.    If any sound or video (or even data/telco) system cabling leaves the building consider using sound and video line lightning devices.  They are available from EDCO, Inc. of Florida and Grommes-Precision.
    http://www.edcosurge.com/products/alarm/alarm.asp
    http://www.grommesprecision.com/precisionelectronics/products/lightningsuppressors/sls.htm

This may be the absolute BEST approach since these guys do this for a living.

Lightning Consultants recommended to me by others:

One colleague suggested this.  Click on their Membership Directory under Professional Members there are 3 from TN.  One appears to be an inspector. Also under Dealers/Contractors there are three from TN: Lightning Protection Institute (LPI)

http://www.lightning.org

If you have a system that consist of a number of lighting rods on the roof all bonded together with multiple down conductors bonded at the ground with multiple ground rods this the LPI’s member expertise.  They however do not endorse the Passive Point Discharge Brush/Dissipation Charge Transfer System DAS/CTS (looks like bottle brushes on the roof) for a number of reasons
listed in their FAQ, if that is the type of system you have. Their reasons are grounded in actual documented research listed on their site. If the research is valid than the DAS/CTS system does not work as advertised.

LPI members successfully do all of their work based on National Fire Protection Assoc. codes (NFPA #780). This has risk assessment tables based on the number of “strike termination devices, interconnecting conductors, grounding system, interconnection or bonding to other building grounded systems, and surge suppression on incoming service lines.

I’ve researched the equipment Dennis Jenkins proposed for the higher voltage and current locations at the Chapel.  He has Hybrid MOV/Selenium Technology for the Service Entrance and the downstream panel units are MOV only. Apparently this is where that technology is at the present, so we must go with it.  The Series Mode Surge Suppression technology isn’t practical at those levels.  The rooftop system protects the building structure.  The interceptors protect sensitive equipment located in the building that are connected to underground utilities, cables, etc.

There were good comments made about the Current Technology products and their parent company, Thomas & Betts.  Some alternatives were offered, but I don’t want to second guess Dennis Jenkins on that since he should have more experience in that area and is desirous of good results here, I’m sure.

Also we discussed the need for the line level audio and RS-485 control lines having the transient suppressors.  In the past we used them only when cables were entering or exiting a building.  Since the lightning pulse was entering the ground and jumping to cables in the ground, the suppressors are recommended here, especially if the cables are not in metal conduit.

Since 90% of the lightning problems occur through the AC power lines, the SurgeX folks feel that is your best protection level anyway.  One thing to remember, the MOV’s are designed to clamp the surges and that causes wear and tear.  Eventually they fail and usually a lamp lights on the panel.  It was recommended to have regular monitoring of the lamps on the panel for signs of failures.

Conclusion

They installed the recommended layered approach with Hybrid MOV/Selenium Technology for the Service Entrance and the downstream panel units.  They installed SurgeX on all sound system and loudspeaker AC power 20A circuits. They installed EDCO PC642 Series RS485 surge suppressor on all data lines to each Intellivox loudspeaker.  As far as I know they haven’t any problems
since.

Wayne Lee
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Lee Sound Design, Inc.
Atlanta, GA