Whether installed in new construction or tenant improvement (TI) in existing structures all electrical boxes installed for a Fire Alarm System must meet the following requirements. The text below is a condensed version of the full code text and does not replace or should be considered as a substitute for the full code text.
.... a box or conduit body shall be installed at each conductor splice point, junction point, termination point or pull point....NEC 70 2017 300.15 referenced in NEC 760.130.
In every location where firewire is spliced or terminated to equipment, there must be a fully enclosed box and it must be red.
Device and junction boxes for fire alarm systems other than the surface raceway type, must be substantially red in color, both inside and outside. Power-limited fire protective signaling circuit conductors must be durably and plainly marked in or on junction boxes or other enclosures to indicate that it is a power-limited fire protective signaling circuit.WAC 296-46B-760
The NEC does allow for the required electrical box to be a listed back box supplied by the device manufacturer for the specific device being installed.
An integral junction box or wiring compartment as part of approved equipment shall be permitted in lieu of a box.NEC 2017 300.15(b)
This means that exterior horn strobes or pull stations which come with weatherproof backboxes can be used as the required box. In these cases, a wire can be installed through a hole in the exterior wall or left in the wall accessible through a low voltage mud ring. The provided device back box would then install over the hole or mud ring.
The fundamental purpose of these requirements is to protect the wire where the jacket has been removed and(or) the wire insulation stripped. A fully enclosed box keeps any foreign material, which may be conductive, from coming in contact with exposed terminals or disturbing a connection. Also, once the firewire jacket has been removed it is no longer a "sheathed" cable. The individual insulated wires are not rated for in-wall or surface exposure.
It is important to understand that the NEC requires all equipment to be installed per the manufactures approved installation instructions.
Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.NEC 70 2017 110.3(B) referenced in NEC 760.130
This means the instructions, include with or online, of fire equipment must be followed. This includes installation locations, attachment methods, operating environment (temperature and humidity) and intended use.
These are the fundamentals of installing electrical boxes for fire alarm systems. The most important code is…
Fire alarm circuits shall be installed in a neat and workmanlike manner……NEC 70 2017 760.24(A)