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I am tasked with running a loudspeaker to a remote building. The total run length is around 275 feet, with the outdoor portion being around 165 feet. The cable is Cat5e 24awg unshielded, silicone filled cable installed in a 2-inch PVC conduit buried 6-12 inches underground.
The loudspeaker amp documentation (Viking PA-2A, page 6) shows that the run length is suitable for the wire gauge, and also states that multiple pairs can be ganged to increase current capacity if necessary. I can use up to all 4 pairs if needed. They also state that step-up/step-down transformers can be used for very long runs (see this), which I will do if the volume is not acceptable.

I said all this to hopefully avoid unrelated replies such as "it won't work/cable size is wrong/etc".

My question is regarding lightning protection. Since the cable is outside/underground for 165 feet, do I need any type of lightning arrester to protect my amp and other electronics?

If so, I'm not sure what type of arrester to use. Most such protection devices are for coax cable, and I've only seen a few screw terminal devices, such as this one, which is only rated for 12VDC. It's my understanding that the amp outputs ~70V to the loudspeaker speaker horns, so I assume this type of arrester would not work.

I would appreciate your advice on how to proceed.

Thanks!

EDIT: I should have known L-Com would have something like this. Is this overkill? I'm only running one pair, not stereo.

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    \$\begingroup\$ Using the transformers would help a lot for a start. \$\endgroup\$
    – Trevor_G
    Mar 8, 2018 at 16:15
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    \$\begingroup\$ Yes, suitable transformers will provide a great deal of isolation. Of course, not much will withstand a direct hit, but having the lines floating, via the transformers, will make them less of a ground path for lightning to want to travel through. SUrge protection on the amp side of the transformer would also be prudent though. \$\endgroup\$
    – Trevor_G
    Mar 8, 2018 at 16:19
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    \$\begingroup\$ Running a heavy ground line down the conduit, spiked to earth at each end would afford the lines a bit of protection too. \$\endgroup\$
    – Trevor_G
    Mar 8, 2018 at 16:27
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    \$\begingroup\$ There is a very informative guide about the effects of lightning and how to protect against them at: legrand.com/files/fck/File/pdf/Power_guide/EX29011.pdf \$\endgroup\$
    – crj11
    Mar 8, 2018 at 17:11
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    \$\begingroup\$ I realize you said that your cable is unshielded, but if it's possible, it'd probably be a good idea to get shielded (braid and/or foil). An example is l-com.com/… \$\endgroup\$
    – Reinderien
    Mar 8, 2018 at 20:54

2 Answers 2

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The usual way for loudspeaker distribution is the so called Constant-voltage speaker system, sometimes also referred as 25/70/100V loudspeaker system.

There is a transformer at the amplifier and one at each loudspeaker. This gives you a fixed impedance at the amplifier as well as isolation, which works as a lightning protection.

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  • \$\begingroup\$ did you mean "isolation"? \$\endgroup\$ Mar 8, 2018 at 18:47
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    \$\begingroup\$ Thanks. I never get the difference in English. In German, it's always Isolation. \$\endgroup\$
    – Janka
    Mar 8, 2018 at 20:16
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A lightning arrestor I've used successfully that has screw terminals is made by Phoenix Contact, possibly others have similar products.

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