atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Security, Alarms and Paging Class 1 Wiring for 70Volt PA Systems

Here in NYC all 70 Volt PA systems are supposed to be installed in conduit (solid or flexible).

While I've seen this ignored more than followed in my career, it is the code.

Does the same apply in the reat of the country? I've heard conflicting stories.

I know in the UK they use 100V & 200V constant voltage systems as opposed to our 25V & 70V systems. I'm guessing that the 100V can be run loose and the 200 requires pipe - anyone know for sure?

No real reason, just idle curiousity. I had a discussion in the saloon the other night with a couple of old telephone guys and the subject came up.

TIA,


Sam

It depends upon the building codes for the specific area you are in. In California it can change from city to city and if usually dependant on fire related issues. (Ceiling type, air return or ducted ceilings etc.)There does not seem to be any stead fast code the everyone goes by.

P.S. Just don't piss off the building inspector !

Here, we were always told that anything over 50 volts had to be in conduit. (Which was why telephone voltage was ostensibly 48V).

But, most of the PA work I've seen has been loose.

Plenum issues not withstanding- that just seemed to be a case of CMP or CMR. This was strictly a voltage issue.

When I do a Constant Voltage PA job, if it's not in conduit, I'll do it at 25volts, or I won't do it.

We have codes for a reason.

Sam

Codes are in place for reasons and should be followed. It is different by states and districts. In Las Vegas, everything has to run in conduit, home runs. It is very tough when you have alot of drops. In Maryland we run without conduit for low voltage unless the superintendants provide the conduit through the elactrical contractors. It is different all over, but I follow local codes wherever I am at.

I've never heard or saw anything like that in Wisconsin

There was a period in the mid-80's in Kansas City, Mo that we went to 25V paging because of a requirement for conduit for 70V paging. Call me naive, but I believed it when I was told that it was 'code'. Of course, it may have been forced thru on a local basis by the good ol' unions?!
And Sam, define 'old phone guys'! I'm 62 and you don't appear to be too far behind me! 'Course you're only as old as you feel, so I'm really NINETY-NINE going on 1 Million! John C. (Not Garand)

What you guys are talking about are local ammendments to the NEC. I won't get into NYC and its quagmire of corruption and union influence, but most of the US relies on the NEC unammended.

The NEC and UL actually have a system in place that makes it easy to know what the wiring requirement is for an amplifier. The system takes into account the voltage, current, voltage and current limiting and other factors and arrives at one of three wiring requirements. This requirement is printed on the rear of the amp near the outputs. The installer or inspector does not consider voltage, wattage or anything else. All they have to do is read the label.

The least stringent is Class 2 or CL2. The label will say "Class 2 wiring permitted". You would use a CL2 listed cable (CL2 printed on the jacket). CL2 wiring does not have to be run in conduit and there are plenum as well as riser versions.

Next is CL3 or Class 3. Use a CL3 listed cable, other than that it's the same as CL2.

Last is Class 1. There is no Class 1 cable because Class 1 indicates that the wiring must follow the same NEC Chapter 3 requirements as power and lighting. That means conduit or type MC, splice boxes and grounds. If for some reason an amplifier is not marked with a wiring requirement it is assumed then to be Class 1.

In actuality, smart engineers have done some clever things with current and voltage limiting that allows even 70 volt very high power amps to qualify for Class 2 wiring. So read the label!

This is a hierarchy, any wiring method can substitute for the ones below it eg: CL3 wiring can be used in place of CL2 but CL2 cannot be used in place of CL3.

By the way, this system is for all power supplies, not just audio amps. When your doorbell transformer says Class 2 on it it works the same way.

-Hal

Hal -

So if a UL listed amplifier says Class 2 Wiring - regardless of the voltage - then I'm OK running the cable loose.

Excellent.

Should I then be real wary of an amp that's not UL listed? (Besides the usual safety reasons)? Obviously I'm not talking about TOA or Bogen, but I've seen some offshore stuff around a lot recently.


Sam

I would be wary of anything that is not UL (or other testing lab) listed. With the junk we are getting from China these days you can't be too careful.

-Hal