Instructions

Application Update
Potter Electric Signal Company LLC: St. Louis, Missouri • Tech Support 866-240-1870
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SLC Loop Performance
Before the 2013 edition of NFPA 72 there wasn’t a requirement to include SLC loop isolation modules when
designing addressable re alarm systems. Unless there was a mandated wiring style (Class A, Style 7 / Class X)
that required isolators, they often weren’t included in the system design. Depending on the make and model of
the re alarm panel, a single SLC could support hundreds of addressable devices. Without loop isolation devic-
es, a single short on the SLC would result in a loss of communication with all devices on the loop.
In the 2013 edition of the NFPA 72 Handbook, there are substantial losses mentioned due to the shorting and
failure of an SLC damaged by re before an alarm could be activated. In addition, there were concerns that SLC
shorts caused inadvertently in part by building operations and activities could result in an alarm system failure if
a re occurs before the trouble conditions are repaired. These concerns prompted the adoption of a new require-
ment that limits the number of addressable devices that can be lost due to a single fault on an SLC loop.
In the 2016 edition of NFPA 72, the limits were changed from 50 devices to one (1) zone of addressable
devices. There was also clarication that the intention of the requirement applied to both short circuit and open-
circuit faults.
PAD100-IM
Isolator Module
The PAD100-IM loop isolation module provides
the required circuit protection to limit the number
of addressable devices affected by a single fault
condition. When using a Class B wiring scenario
each module provides two (2) isolated “legs” of the
circuit. This limits the number of addressable devices
connected to each leg and facilitates code compliant
system design.
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