Fire Alarm Underground Conduits

Is it OK to Install Fire Alarm Cable underground?

Post Indicator Valve  with Fire Department Connection

A common task when installing a new fire alarm system is undergrounds. Typically when a C-16 or fire protection (fire sprinkler) contractor installs their incoming lines they will at the same time install the necessary fire alarm underground conduits for the connections to the backflow prevention switches (OS&Y Outside Screw and Yoke) or PIV (Post Indicator Valve) switches. However, sometimes this task could be a part of the fire alarm contractor's scope of work. If you find yourself installing underground conduit or direct burial cable make sure to follow all of the national codes and regulations.

Direct Burial Cable as an Alternate to Conduit

Backfloe Preventor with OS$Y Switches for Fire Alarm

Some contractor's may choose to use direct burial cable also referred to as UF Cable commonly identified by its grey coating. Direct burial fire alarm cable not protected in conduit must be installed at a depth of 24" below grade with either schedule 80 PVC or Rigid conduit stubs up to your box. When fire alarm cable is installed within plastic conduit it must be 18" deep and installed with schedule 80 PVC. This is a more durable plastic conduit (grey color) than the common household irrigation lines. The best way to install these conduits or cable is with a Ditch Witch. Simply set the depth and go.

Junction boxes that are run out into the middle of a remote area without an anchor point must have the schedule 80 PVC embedded in the concrete to support the box. Another method is to attach the box to a post that is either driven or buried in the ground 18" and connects directly to the schedule 80 PVC conduit. Junction boxes should be installed at least 12" above grade but not more than 18" for the unattached method.

See also conduit bending videos.

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Direct Burial Cable for Fire Alarms

Did you know you could direct bury fire alarm cables if codes and standards are followed?

Have you ever used direct burial cable in your fire alarm installations? Typically in fire alarm you will not see much of it as most of our outdoor work is typically in Rigid conduit or schedule 80 PVC.  Also a small portion of our fire alarm designs involve running out side for connections.  Without getting too deep in the design aspects, more than likely, if you are running circuits outside, are likely for a PIV (Post Indicator Valve), or Backflow Preventor with OS&Y switches (OS&Y standards for Outside Screw and Yoke)

Direct burial cable is a cable that is designed and U.L. approved to be installed directly in trenches without the need for conduit or other raceways.  The wires themselves are encased with what is known as a thermoplastic sheath that seals out moisture to help protect the wires. Direct burial cable often referred to as UF Cable and commonly ships with a grey jacket. However, there are some wire manufacturers such as Beach Wire and Cable, Arrow Wire and Cable, and Windy City Wire that make their own listed direct burial cable and it comes in black. Please note that this type of cable is only listed for this use if it is installed at the proper depths.

An easy way to notice the difference between standard non-metallic sheathed cable (NM) and underground feeder cable (UF) is the coating around each cable within the jacket. NM cable is simply a jacket to house multiple conductors whereas the UF cable separately coats each conductor.