atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Security, Alarms and Paging Large PA system installation

Hal -

You're absolutely correct about Class 1 wiring. Usually most Amps 100watts or larger require class1 for the 70Volt output. 25 volt output does not require class 1 but will require substantially bigger amplifiers.

Class 1 wiring can be installed in flex (mc,bx) and does not necessarily have to be installed in conduit.

As far as life safety systems - I'm not familiar With the code in DC or Virginia, but in my experience that's usually associated with the fire alarm system.

Sam

Wow, good point, Hal. Their specs state that this PA system is not planned to be used for everyday paging; more of an emergency announcement system. I'm not sure if that falls into the category of a life safety system, but I'll surely be asking the question first thing on Monday.

This is a 100 year-old building where we have been maintaining for their ISDN system for several years. We never paid any attention to the existing PA system since that wasn't within the scope of our support contract. The building is being gutted, but since it is a historical building, they won't allow any new drilling, etc. This is why we have to re-use the existing speaker enclosures, Wiremold and conduits. Since they gutted all of the voice cabling, I'm sure that they did the same with the PA cabling too. Even if there's anything left, I'm sure that it would be cheaper to replace it all rather than to hunt through the remnants.

My plan is to use multiple 60 watt amplifiers, one in each of the three closets on each floor. It appears that CL2 wiring will be OK for this environment.

I do have to ask a question about NEC requirements on this: It states that the code does not apply to federal government installations. This building is owned by the Feds. Does this stipulation apply to installations by federal employees or to installations within federal buildings by outside contractors? Should we discuss this with Mr. Holt's people?

Geez, I'd be happy if I knew half of what you forgot.

Ed, I did quite a bit of work in Federal buildings. I was always told that they fell under the National, not the local building codes. So in NYC, the less stringent National Electrical Codes were used, not the more stringent NYC codes.

If that's the case then the NEC would apply.

Sam

Actually you just did, I just came from over there. The answer is to ask the AHJ what codes apply. There should also be something in the RFP specs that you got from them. There is nothing in the NEC that exempts federal buildings but the feds might exempt themselves from the NEC in whole or in part I would assume.

This does sound like a life-safety system from what you said. Is there a design for this or did they just dump it on you to do a design-build? If so what do the specs say? I believe Life-Safety is covered by NFPA 101 (The NEC is NFPA 70). Something also to talk over with the AHJ and fire marshal. What is required in govermental buildings? If it is Life-Safety it's probably best to sub it out to a company who has experience in that area.

-Hal

They did just dump it on us as a sub for the new prime contractor. We've been given very sketchy specifications since this was apparently an oversight on the agency's part. There was a pre-bid conference held on-site and one of the potential bidders noticed the existing speakers. The agency quickly scrambled together an addendum that basically states "the existing paging system shall be replaced using existing speaker enclosures, conduits and other wiring pathways". All of the original wiring and amplifiers have apparently been removed as a part of the gut job. That hardware is probably already listed on E-Bay as we speak.

This job is starting to stink to high heaven. As a sub of a sub for the prime contractor, I see this as becoming a huge problem. My boss will insist that we bid on it anyway. It is a huge job, but laced with many unknown issues and potential liabilities. I really dislike federal government projects for this exact reason.

Well then in the absence of anything else that is what I would bid on. Just make sure you write an ironclad contract with specs for them to sign before you do any work. Then if they decide to do something else they can't blame you and it becomes a change order.

-Hal

It would be handy if they'd left the old cable as you could probably have used it for drawing new cable through the conduits.

Multiple 60 watt amps per floor means you will have to distribute audio at line level to multiple locations, as well as switching signals for zone switching, local source over-ride etc - and it will make using a UPS much harder.

Much better to cable back to a central amplifier room. If you can do 3 zones per floor, put in 1 amp per floor, sized for 1.5x floor load. Then when one amp fails, you can split that floor's zones across three other amps.

You also have everything close to hand in one room and can carry out all testing and maintenance without having to go onto the office floors.

70V wiring will run happily over 100s of metres (miles if you lump-load the lines to compensate for cable capacitance): here's the control room of a Bultin's holiday-camp installation by Messrs. Tannoy.

Driving 150 speakers per floor with a 60w amp! You need to rework that math. Recently had a project requiring some special audio considerations and Parts Express helped me out. The customer was extremely satisfied with the end product.

No, we are proposing three 60 watt amplifiers per floor, one per closet. The more realistic count of speakers per floor is about 90 at most, so roughly thirty speakers per amplifier. Set at 1/4 watt taps, we'll be fine. Thanks for the concern though!

I ended up going with a 100% Bogen solution. The price came out right and the customer didn't even flinch when we presented it. It took my breath away personally, but I'm not used to pricing projects into the six figures.

That's government pricing for you.