sundance-communications.com/forum Forums Wiring - Telecom Carriers - Trunks & Services Security, Alarms and Paging 70 volt questions

And my electrical license prohibits me from working on anything that uses more than 90 volts.

They (the all-knowing government) seem to forget (or never knew) that ringing is, indeed +/- 90 Vdc, but it is added to the -48. So POTS circuits have a peak of -138.

Shhhhh! Quiet, they'll hear you.

-Hal

Hal, thanks for the info...I was trying to jog my memory. I knew about those code requirements...but I wasn't sure how much it is enforced.

Unless there are local amendments the NEC makes no stipulation regarding amplifier output voltage or power and wiring. Rather, it defers to UL to determine what the speaker wiring should be. UL writes the specs and manufacturers submit samples of their products to UL or another accredited testing lab for compliance.

Speaker wiring, like any wiring from a low voltage power supply or transformer is divided into three categories; Class 1, CL3 and CL2 as determined by the UL testing procedures which does take voltage and current into account. UL requires that manufacturers print either "Class 1", "CL3" or "CL2 wiring required" next to the output terminals of the amp. This makes it easy for an installer to determine the wiring requirement.

The hierarchy is Class 1, CL3 and CL2. That means a Class 1 wiring method can be substituted for both CL3 and CL2. CL3 can be substituted for CL2.

Both CL3 and CL2 wiring is the familiar PVC or Plenum jacketed cable. It must be marked with CL3 or CL2. Both can be run exposed and without conduit and boxes.

Class 1 however is much more restrictive. This wiring method is the same as for power and lighting so it must comply with NEC Chapter 3. This means conduit and/or other Chapter 3 wiring method, boxes and grounding- from the rack all the way to the speakers.

I'm not sure how many amps are manufactured today that require Class 1 wiring. Not all manufacturers include that information in their literature so you almost have to buy the amp first to know what to do with the rest of the system. You can be assured though that small amps under 200 watts are going to be either CL3 or CL2.

Even though these are the code requrements, not many installers are familiar with them and inspectors aren't well versed in low voltage either so you can expect just about anything.

-Hal

But -138 is significantly less than 50, so we're clear!

Yeah, right! 188 volts less! And he-- yes, it'll hurt! What will really hurt is that part of your body that you whack on something hard, or sharp, or both, during the 'voltage test' period! John C.

Arthur I always thought that ringing was 90-105v AC with -48 volts added for tripping the ring.course that was way back in the days of dial long line and step by step switching.

Right but it's really called superimposed. What happens is the 48 volts biases the AC ring voltage zero reference up or down depending on the polarity. A negative DC voltage will add to the negative peak of the AC waveform. (-48)+(-105)= -153.

-Hal

And that, folks is why the NEC people decided to stick with 50 volts and call it a day. They would never understand that description of how phone lines work.

Hal, you should plant a post over at Holt's place with those details and see how many GFCI's and AFCI's they recommend for your CAT5 cable.

Sounds like fun.....

My bust, I forgot that in 'telephonese' 48V is - in relation to ground! Hey, I'm old, I can forget anything I want! My excuse is that I came out of electronics, where negative voltages aren't very common. Unless you start talking about pentode tubes.
Hal, if you do plant a post, please be sure to give us a link. John C.