Fire Alarm Question: Line Isolators

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They are to isolate short from propagating and dragging down the entire circuit. It is used for Class A looped type circuits.

Ok, so how often would a isolator be placed - after how many devices on a circuit? Also what is the general limit to the number of fire alarm devices you can have on a circuit?
 

nhfire77

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Ok, so how often would a isolator be placed - after how many devices on a circuit? Also what is the general limit to the number of fire alarm devices you can have on a circuit?

Design will determine this. In the 2010 NFPA 72 there is class X circuits, in which an ISO module is between each device and one at either end of the SLC prior reaching the panel. Pre2010 it was called style 7. Very few fire alarm systems need or require such isolation.

I use ISO modules on a per floor or per tenant space basis, when I think the system should have it, (which is rarely if ever due to cost since its not required in the prescriptive code). Job specs laid out by the an engineer or designer normally dictates their use.

The number limited per SLC is manufacturer specific.
 
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