Checked 17 Oct 2026 against public cable manufacturer specifications and equipment wiring instructions. By the Alarm Ladder editorial team.
“Fire alarm cable” describes a family of products. Selecting one means matching its listing to the installation environment, its conductors to the circuit, and its electrical properties to the equipment. A red jacket or a familiar gauge cannot answer all three questions.
This guide explains the vocabulary used on cable reels and specifications. For the circuit roles behind those specifications, read NAC vs SLC circuits. Installation decisions need the adopted code edition, project documents and the selected equipment's instructions.
FPL, FPLR and FPLP describe different uses
These markings identify power-limited fire alarm cable types. Start with NEC Article 760 in your own adopted edition for fire alarm circuit requirements. We cite the article number without reproducing its text or substitution tables. Do not apply a power-limited cable description to every circuit inside a fire alarm system.
- FPL: general-purpose power-limited fire alarm cable. Southwire's direct-burial fire alarm product identifies FPL and a general-purpose rating. Its additional burial suitability belongs to that product; the letters FPL alone do not establish that suitability.
- FPLR: riser-rated power-limited fire alarm cable, associated with vertical riser applications. Belden identifies its 5020UL cable as FPLR and lists indoor riser suitability. A riser marking alone does not establish suitability for an environmental-air space.
- FPLP: plenum-rated power-limited fire alarm cable, used for applicable environmental-air spaces. Southwire's FPLP stranded unshielded cable expressly identifies plenum use and a UL 1424 FPLP listing.
Treat those as general descriptions, not permission to install a particular product anywhere bearing a similar room name. An above-ceiling area needs its actual use established from the project information. Check the full route, including transitions between spaces, before selecting the cable.
Reader note: A plenum listing describes cable fire-performance suitability for that application. It does not establish that a circuit will keep operating during a fire. Outdoor exposure, wet locations, burial and circuit survivability require their own supporting product and project information.
What 14/2 actually means
In this context, 14/2 means two insulated 14 AWG conductors. It says nothing by itself about plenum or riser suitability, shielding, conductor construction or compatibility with a panel. Do not assume the notation includes an equipment grounding conductor. Read the construction details for every conductor and any separate drain wire.
Belden's 5120FL is one example: two 14 AWG solid copper conductors, an overall shield and an FPLR rating. Its 6100FL also has two 14 AWG conductors and shielding, but uses stranded conductors and an FPLP rating. The shorthand size is the same; the products differ.
Within the AWG system, a smaller gauge number denotes a larger conductor. That helps explain why increasing conductor size can reduce resistance, but it does not make 14/2 the default answer for every NAC or SLC. Check the equipment's permitted conductor sizes and terminal requirements.
Shielded, unshielded, solid and stranded
A shield is a conductive layer around the insulated conductors. A shielded specification also needs the manufacturer's termination instructions: the drain wire and foil are not spare circuit conductors. Unshielded cable omits that surrounding shield. Shielding is a system compatibility decision, rather than an automatic upgrade.
The Notifier SLC Wiring Manual recommends twisted unshielded pair for the systems it identifies and gives model-specific instructions for shielded wiring. Follow the manual for the actual loop controller instead of transferring another panel's shield practice.
Solid means each conductor is a single wire; stranded means it comprises multiple smaller wires. Belden's examples above show both constructions at 14 AWG. Compare the stated resistance, handling limits and termination compatibility instead of treating construction alone as proof that one product is suitable.
Fire alarm wire color code: read the legend
Separate the outer jacket color from the insulation colors inside it. Belden's 5120FL specification lists black and red conductor insulation, while its product ordering information identifies a red jacket. Those are product details, not a universal code rule assigning every fire alarm wire a function.
Use the project legend, cable schedule, terminal markings and equipment instructions to establish identification and polarity. Carry that identification through splices and records. When existing colors disagree with the drawings, have the discrepancy resolved before making a connection. Color alone is insufficient evidence of function.
Cable choice and voltage drop
The fire alarm wire size calculator shows which AWG keeps the last appliance in range for a given load and run. For a simple two-conductor DC circuit, voltage loss follows voltage drop = current × circuit resistance. Include both outgoing and return conductors. Longer cable and higher current increase the loss; lower conductor resistance reduces it. Distributed loads need a method that accounts for which current flows through each segment.
Use the voltage-drop formula guide alongside the fire alarm voltage-drop calculator. The calculator addresses NAC calculations; it does not establish SLC data performance. SLC selection also needs the panel's resistance, capacitance, length and topology limits.
For study, trace one cable selection from the drawing to the specification and calculation. The submittals and layout guide connects those documents. Return to the Alarm Ladder overview or try the Level II diagnostic to identify your next study topic.
For loop wiring practice and fault-finding on signaling line circuits, see SLC loop wiring and troubleshooting.
Sources
- General-purpose FPL fire alarm cable, Southwire. Retrieved 17 Oct 2026.
- 5020UL riser cable, Belden. Retrieved 17 Oct 2026.
- FPLP stranded unshielded cable, Southwire. Retrieved 17 Oct 2026.
- 5120FL solid shielded cable, Belden. Retrieved 17 Oct 2026.
- 6100FL stranded shielded cable, Belden. Retrieved 17 Oct 2026.
- SLC Wiring Manual, Document 51253 Rev U9, Notifier. Retrieved 17 Oct 2026.