Does anyone know he possible cause of loud static noise in a Simplex 4010 speaker system? We have replaced the audio control board but there was no change. It is so loud that you cannot hear the recorded voice message that plays to evacuate the building.
Maybe it’s SLC chatter? This could happen if the SLC uses non-shielded wiring and is in the same conduit as the speaker wire. (I have never heard of it to this extreme, though!)
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This is a typical issue dealing with a code violation art. 250.94 regarding grounding differential issues. You are passing current through the NAC circuit based on the fact that you have two different grounds associated with the panel. However, if you can not correct this problem by creating a single point ground, using a FA 60NC, for 34.4V or FA90VB for higher operating voltage should do the trick. Both are UL497. These are not your typical surge suppression rather they have a tank circuit in there that will attenuate the noise significantly. Adding an additional unit on there will reduce the noise as well especially if you use one on each end of the wire. I also have FA 30 BH or FA 60NC that can be also used on SLC circuit if they are experiencing the same issue. You can find these on Amazon, if you don’t want to go direct to me.