If the drain wire is insulated relative to the MC jacket, then it should remain isolated from the j-box and any raceway. It is typically terminated on the control panel end only. A drain in contact with the j-box when it should be isolated is unrelated to the condition of the communication conductors making contact with the drain or the MC jacket.
#53337 - 06/22/0504:44 PMRe: Addressable Fire Alarm
Have done several addressable systems, and have had problems that were instantly gone when an untaped shield or drain wire was found in contact with a steel box mounted on steel studs. They were not ground troubles, but various data problems. I usually tape each cable's drain separately before connecting them to the other cables because it is so much easier to take apart and put together the cables later if you have to troubleshoot. I have never seen anything like these supervised systems that makes a man have to do so much unwirenutting and rewirenutting over the course of getting all the bugs out.
T-tapping was always OK with the large well known manufacturer whose product we installed...the system instantly goes into a trouble condition if any device does not report in, no EOL needed. This is only the initiating circuit, however. The audio/visual circuits in the systems we did were always run in supervised loops with no t-taps. They were not addressable.
[This message has been edited by poorboy (edited 06-22-2005).]
#53339 - 06/22/0507:10 PMRe: Addressable Fire Alarm
Yes - be sure to insulate that drain wire. If "t" tapping just join all the drains together and tape them very good. You only attach those drains at the panel- any where else and you will have troubles when you turn on the system. I do not like "T" tapping. sticking with straight in and out makes trouble shooting much easier. Just my 2 cents
#53340 - 06/22/0508:02 PMRe: Addressable Fire Alarm
It is true that the big advantage of an addressable system is the ability to T-tap.
There should be no problems because each device (smoke / heat detector and pull stations ) will have thier own unique "address". Each device periodically is verified by the control panel and if the device does not respond the system goes into trouble. So yes, we will be T-tapping but we will keep it to a minimum. The horn/strobes are looped with an E.O.L. resistor.
Also, as to keeping the drain isolated from ground. I was just told "Thats the way we always did it." I hate that answer. I always want to know why. Thanks for all the responses.
#53342 - 06/22/0508:35 PMRe: Addressable Fire Alarm