Fire alarm bell supervision

[Fireguy1980]

I am fairly new to fire alarms and have an issue with a verification of bell circuits. I have 2 bells on a signal circuit (class b with EOL resistor), I can create an open and a ground on 2 wires, but on the other two I get the open but no ground on 1 wire, and an open and when I try to get a ground, it clears the circuit and the panel is clear? What is going on?

 

[nhfire77]

I am fairly new to fire alarms and have an issue with a verification of bell circuits. I have 2 bells on a signal circuit (class b with EOL resistor), I can create an open and a ground on 2 wires, but on the other two I get the open but no ground on 1 wire, and an open and when I try to get a ground, it clears the circuit and the panel is clear? What is going on?

I'm not entirely sure what your getting at, let me try:



Is the line side the 2 wires you get an open and a ground fault (that's normal)

Then the load side must be the other. If so, when the load side is not connected to the line side(connected to the panel) you will not see a ground fault. There is no path from the bell circuit terminal to ground, assuming both legs of the load side are lifted from the line.
A ground fault on only one side could indicate a t-tap, diode present, 2nd ground fault location, miswire etc..... If it is not connected to the line side conductors


If the panel goes normal when you ground a conductor, there is a 2nd ground fault, that is on the same conductor, it is completing the circuit to the eolr, as to why a ground fault is not indicated makes me think I didn't understand fully. Unless thehigh resistance ground fault is above the panel's detection threshold, but sees the resistor-which is odd.

I don't recommend intentionally grounding circuits as a test method, you could kill the panel. If there were more than one faulted circuit, you could induce current through the panel from a foreign source, among other possible issues.

 

[Simplex]

Basic class B supervision

Basic class B supervision

Ok.. Try to keep up...

F---\    /----\    /-----\
A    bell      bell       EOL
C     #1        #2       /
P---/    \----/    \----/[/FONT]

hopefully that looks right.

Do NOT loop wires under screws at the Bells. Cut your NAC's and terminate both leads under one screw. Keep your pluses and minuses consistent. The EOL is non-polarized.

If you did it right, the panel will show normal. If it shows a Trouble and the trouble is a GND fault, get your voltmeter, switch it to resistance, and meter from + to GND, and from - to GND. One should show open circuit, the other will have some resistance (which is bad). Split the NAC in half and follow the bad conductor until you find where you nicked the jacket and cause it to short to the raceway. If you can't hack a voltmeter get out of low-voltage work and stick to power and lighting. If it shows an Open or a Short, well go find the open or short. You know what an open and a short is, right?

Two bells and an EOL on one NAC is childs play. There shouldn't even be a question at all about it.