To the group, I am seeking advice as to the best methods of protecting a Public Address system against recurring lightning damage. The system uses several commercial PA amplifiers, each driving several speakers at indoor and outdoor locations. There are also several locations where microphones can be plugged in. The longest speaker wires may be up to 250 yards long. It is believed that the charge is being coupled to the speaker wires where it then returns to ground at the amplifier location within the building, destroying the solid state devices within the amplifier. A technician has added fuses to all external microphone inputs and speaker outputs. While these have blown several times during storms without obvious damage to the amplifiers it is my belief that fuses are generally too slow to protect semiconductor devices. I am seeking advice as to surge suppression devices. System particulars are as follows:
1) The PA amplifiers have 70 volt outputs. All speakers are transformer coupled. 2) All microphones use standard XLR connectors. They plug into metallic conduit mounted jacks at locations inside and outside the building. The outside microphones are unplugged during storms. 3) The amplifiers are located on the second floor of the building. Each amplifier is dedicated to a set of speakers at one location. The amplifier driving the longest wires is the one which most often has to be replaced. 4) The building is in a location known to be susceptible to lightning activity. Electrical appliances have been destroyed on at least two occasions. 5) All protective grounding efforts to date have been made to the conduit. I am recommending that this be supplemented by driven rods. It is pretty easy to buy commercial surge suppression devices for the ac lines. I feel I need advice as to the best methods to protect the audio inputs and outputs. For the 70 volt outputs I am thinking of using gas tubes to earth where the wires enter the building supplemented by MOV, Tranzorb, or other devices near the amplifier location. I welcome suggestions as to device types. For the microphone inputs I am thinking of using semiconductor transient voltage suppressors near the amplifier. Again, any suggestions are welcome. Thanks in advance for any advice and guidance. Scott Lacey sco...@world.std.com ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
