sundance-communications.com/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring 44 speakers at car dealership...

Great Idea, jb.

We were told NOT to do that in I/R class due to the antenna affect. Did it all the time when the place was fed via open wire in lieu of the fuses they no longer allowed us to use. (1293C can).

I've heard the antenna thing too Ken, but I've never had any induced interference. We did the same as you if we didn't have any fuses on open wire.

I've actually seen the Bell installers here make the coil on their ground wire coming from the protector. I mentioned it to one guy and he informed me he does it so there is some slack in case somethings pulls on the ground wire. His thoughts were that it would give rather than pull out of the split bolt. I told him he was creating an obstacle course for the so called "quick ground path." I think he mumbled something about not knowing what the hell I was talking about. Oy vey! :rolleyes:

I have seen ground blown in two at a 90 degree bend. I was always told to keep it straight or gradual bends.

Another point, since we are talking about lightning, is protectors. All outside wire needs a protector where it enters the building just as we do with telephone. Ditek makes protectors for 70 volt and other speaker lines.

-Hal

I got burned once with interfearance. Had to rewire a large place. Did it in peices until a spoke with
engineer at JW Davis. I guess thats why I do it in most places that have possible problems.
After more research it seems that there are divergent opinions on this even from the manufactures of the dang equip.
Also had a Mexican market we did with 70 Bogen EZ1
spk and Tandem TPU 100 amps. (Jammin Mexican music big time) Cabler ran spk cables short and we ran cat 5 about 15 feet under backboard to get to cables.
That stuff bled over to MOH and sometimes phones,
no way to tone a cable except to pull plug on amp.
Change the short run to shield and it went away.
Have had high volume music on other jobs without shield without problems. ????

The twist on the wire is far more important for talk back applications than using a shield. I have run 100's if not 1000's of miles of cabling in schools for intercom. These typically use 25V line because the impedances are lower than 70V and has better common mode rejection against picking up noise. I use 18/2 twisted, stranded wire. If you are running powered speakers, they usually have a higher input impedance and accept a line level signal of perhaps a few volts unless they have an attenuator to accept 25 or 70V line. Due to the higher input impedance they are more prone to picking up noise and shielded cable would be better used in this application, although 22 guage is more than sufficient. For lightning protection, a 150V varistor from each side of the speaker line to ground will offer all the protection you need except in the case of a direct hit, in which case nothing will protect the amp or speakers. The advantage to running 70V line is less line loss, you can use a smaller guage wire for longer distances.