Screened vs Unscreened Fire Alarm Cable: What Should Installers Check?
When specifying fire alarm cable, installers often face a practical decision: use a screened fire alarm cable or an unscreened cable. The shielded vs unshielded cable choice matters because fire alarm circuits carry signalling and, in many systems, power to devices. The selection should match the circuit function, route, environment, and expected interference.
FireFactory supplies screened fire alarm cable options for commercial projects, and installers should confirm technical details before purchase.
How Screened Fire Alarm Cable Works
A screened fire alarm cable includes a conductive layer between the insulated conductors and the outer sheath. This screen is commonly formed from braid, tape, or foil, depending on the cable design. The screen provides a barrier that can reduce the effect of electrical noise from nearby equipment, lighting, and power wiring.
In a fire alarm system, the cable may carry low level signalling to detectors, modules, and sounders, or it may carry power to devices, depending on the system design. A damaged or poorly terminated screen can reduce performance or create fault conditions. An unscreened cable has no conductive shield and is often suitable for lower risk routes where the system design does not require a screen.
Key Checks Before Selecting a Cable
Installers should check the cable specification against the circuit function and the physical route. The following checks help avoid rework and protect signal integrity.
- Circuit function: Confirm whether the cable carries signal, power, or both, and identify the maximum expected current and voltage drop requirements from the design.
- Route environment: Note exposure to heat, sunlight, moisture, chemicals, mechanical abrasion, and vibration.
- Interference sources: Identify nearby power cables, switchboards, variable speed drives, industrial machinery, and lighting.
- Screen type: If a screen is used, check the screen construction, continuity requirements, and termination method required by the system manufacturer or cable data.
- Sheath and colour: Confirm the sheath construction, required marking, and any site colour coding requirements.
- Length and quantity: Account for pull lengths, spare length, future expansion, and cable tray fill.
Screened Fire Alarm Cable vs Unscreened Cable
The table below helps installers compare the two options during a site walk.
| Factor | Screened fire alarm cable | Unscreened cable |
|---|---|---|
| Interference | Offers a conductive barrier that can reduce noise from nearby sources. | Relies on routing, separation, and cable selection. |
| Typical route | Consider where the cable passes near power, machinery, switchgear, or dense cable trays. | Suitable where interference is low and the design allows it. |
| Termination | Requires attention to screen integrity, gland, seal, and termination method. | Simpler, but still requires correct stripping, dressing, and termination. |
| Common failure points | Broken braid, lifted screen, poor screen connection, damaged sheath. | Signal interference if routed near noise sources, mechanical damage, incorrect cable size. |
| Selection check | Confirm screen construction and termination requirements from the cable data. | Confirm conductor size, sheath, and route protection from the design. |
Commercial Facility and Purchasing Considerations
Commercial sites often mix fire alarm circuits with power, security, data, and control wiring in shared spaces. A screen can be valuable in plant rooms, machine rooms, data centres, workshops, manufacturing floors, and high density office buildings. The cable should also suit the local access method, such as cable tray, conduit, or trunking, and the way it is supported and protected.
When purchasing, installers should compare the technical data rather than relying only on cable name. Conductor size, insulation, screen construction, sheath, and marking all affect installation and performance. The FireFactory cable range, available on the FireFactory cable page, gives B2B buyers a place to compare screened fire alarm cable and unscreened options for Australian projects.
Installers should also allow for on-site inspection before termination. Check the cable for cuts, kinks, lifted sheath, broken braid, dirty conductors, and damaged screen. A small defect at the cable end can be missed during a visual check and may become a fault later.
Frequently Asked Questions
What is the main difference between screened and unscreened fire alarm cable?
A screened fire alarm cable has a conductive shield around the conductors, while an unscreened cable does not. The screen can reduce the effect of electrical interference from nearby power or equipment.
Can unscreened fire alarm cable be used in commercial buildings?
Yes, where the route and system design do not require a screen. The cable should be selected for the circuit function, conductor size, sheath, and installation environment.
How does an installer know when to use a screened cable?
The decision should follow the system design, route survey, and interference risk. Screened cable is often considered where the fire alarm wiring passes near high current power, machinery, switchgear, or other noise sources.
What should be checked before terminating a screened fire alarm cable?
Check the cable for damage, confirm the screen is intact, and follow the manufacturer termination instructions. The gland, seal, and screen connection should suit the cable construction and the installation conditions.
Does screened cable remove all interference from fire alarm circuits?
No. A screen helps reduce interference, but correct routing, separation, conductor size, and termination still matter. Poor installation can still allow noise or signal loss on a screened cable.
Conclusion
Installers should choose screened or unscreened fire alarm cable based on the circuit, route, environment, and system design. A quick route survey and a careful check of the technical data help reduce faults, rework, and site delays.
For B2B projects, FireFactory provides access to fire alarm and security cable ranges for Australian trades and fire companies. Contact the FireFactory team or browse the FireFactory cable page to compare screened and unscreened options for your installation.