Addressable fire alarm systems depend entirely on the reliability of communication loops. Every detector, module, and sounder communicates back to the Fire Alarm Control Panel (FACP) over a two-core cable. If the cable is not chosen correctly, it can lead to data loss, loop errors, false alarms or complete failure in emergencies.
In India, two cable types are most commonly used in addressable fire alarm loops:
- FRLS (Flame Retardant Low Smoke) Cable
- Shielded Twisted Pair (STP) Cable
This article compares both options in detail, from signal performance and attenuation tests to compliance with BIS/ISI standards, so you can confidently choose the right cable for your project.
Why Cable Selection Matters in Addressable Fire Alarm Systems
Conventional fire alarm systems only trigger signals, but addressable systems transmit digital data over communication loops. These loops carry:
- Detector addresses
- Device status
- Fire/fault/short circuit alerts
- Maintenance information
- Power/reset commands
Any drop in signal quality can cause:
- Loop communication failure
- Multiple device offline alerts
- False alarms
- Delay in fire reporting
- Non-compliance with NBC or BIS standards
So, selecting the correct core type, conductor size, insulation and shielding is critical.
Cable Standards & Compliance in India
Indian fire alarm cabling must comply with:
- IS 1554 (Part 1): PVC-insulated cables
- IS 694: Low voltage cables
- IS 14494: FRLS properties
- IS/IEC 60331 & 60332: Fire resistance
- NBC 2016 (National Building Code)
- UL 1424: For imported fire alarm cables
- EN-54 compliance (for global brands like GST, Honeywell, Bosch, Siemens)
Local AHJ (Authority Having Jurisdiction) may also demand ISI marking and CE compliance.
What is FRLS Cable?
FRLS (Flame Retardant Low Smoke) cables are widely used in fire detection systems across India.
Features:
- Flame retardant (IEC 60332-1 compliant)
- Low smoke emission
- Low halogen release
- Single-core or multi-core variants
- Available in 1.5 sqmm or 2.5 sqmm
- Generally unshielded
- Inexpensive and easily available
Common Uses:
- Conventional fire alarm panels
- Public buildings, schools, hostels, hospitals
- Wiring inside conduits and false ceilings
What is Shielded Twisted Pair (STP) Cable?
Shielded Twisted Pair is designed to reduce electromagnetic interference (EMI) and signal attenuation, which makes it ideal for digital data transmission used in addressable systems.
Features:
- Two twisted copper conductors (18 AWG/1.5 sqmm typical)
- Aluminum Mylar shielding
- Often includes drain wire
- Available as red FRLS/STP hybrid
- High noise immunity
- Better communication reliability
Common Uses:
- Addressable GST, Honeywell, Siemens, Ravel and Morley loops
- High-risk commercial and industrial projects
- Long loop runs over 1,000m
FRLS vs Shielded Twisted Pair – Feature Comparison
| Feature | FRLS Cable | Shielded Twisted Pair (STP) |
|---|---|---|
| EMI Resistance | Low | High |
| Smoke Emission | Low | Very Low (if FRLS-STP) |
| Flame Spread | Controlled | Highly controlled |
| Attenuation (over 1km) | Higher | Lower |
| Use in Addressable Loops | Limited | Ideal |
| Loop Stability | Moderate | Excellent |
| Cost | Low | Slightly higher |
| Compliance | ISI/BIS | BIS/UL/NBC compliant |
| Accessibility in India | High | Moderate but growing |
Why Addressable Panels Prefer STP
Addressable fire alarm systems transmit digital address signals that require clean communication without distortion. STP cables:
- Prevent crosstalk in multi-device loops.
- Maintain signal strength over long runs.
- Reduce false fire/fault triggers.
- Comply with GST and Morley installation manuals.
- Help maintain system programming integrity.
- Reduce cost of repeat cabling and repairs.
Signal Attenuation Explained
Signal attenuation refers to the loss of data strength as it travels along a cable.
Factors that affect attenuation:
- Cable length
- Conductor resistance
- EMI from lifts, DGs, HVAC, motors
- Shielding quality
- Twisting pattern of cores
Fire alarm loops often exceed 1 km, especially in hotels, malls, IT parks, airports and hospitals. At these distances, FRLS cables can cause data distortion.
Signal Attenuation Tests – FRLS vs STP
To compare both cables, a typical attenuation test setup involves:
Test Parameters:
- Cable length: 500m & 1200m
- Load: 32 addressable devices
- Panel type: GST / Honeywell / Morley IAS
- Frequency: 2 kHz – 5 kHz digital signals
- Noise sources: UPS room, lift core, HVAC cabling
Test Observation Table
| Parameter | FRLS | Shielded Twisted Pair |
|---|---|---|
| Signal Loss @ 500m | 4–6 dB | 1–2 dB |
| Signal Loss @ 1200m | 8–12 dB | 3–4 dB |
| EMI Interference | High | Very Low |
| Loop Fault Alerts | Frequent | Rare |
| Device Drop-off | Yes | No |
| False Alarms | Possible | Unlikely |
Interpretation:
STP maintains cleaner signals over long loops, especially in electrically noisy environments. FRLS is adequate only for short runs below 300m with low EMI.
Recommended Cable for Different Projects
Small Buildings (< 10 devices per loop)
- FRLS can be used
- Max run: 200m–300m
- Recommended for standalone setups
Medium Commercial Projects
- Hybrid FRLS + STP
- STP for loops, FRLS for power
- Loop length up to 800m
Large Complexes / Malls / Airports
- Shielded Twisted Pair only
- Use 1.5 sqmm, ISI-marked
- Supports long loops and 100+ devices
Misconception: “FRLS is always enough”
Many Indian installers use standard 1.5 sqmm FRLS cables even for addressable loops, but panel manufacturers like GST, Honeywell, Ravel and Siemens recommend:
- Twisted pair
- Shielding
- Low resistance conductors
Improper cabling may pass initial testing but will fail during commissioning or event conditions.
NBC and IS Standards Recommendation
The National Building Code 2016 states that:
“Cables for fire detection and alarm systems must ensure uninterrupted operation under fire and mechanical stress.”
For addressable systems, additional shielding is now preferred, especially in:
- IT Parks
- Metro stations
- Industrial buildings
- Data centers
- Hospitals
Cost Comparison (Per Meter – India Market)
| Cable Type | Cost Range (₹/meter) |
|---|---|
| FRLS 1.5 sqmm | ₹25–₹35 |
| STP FRLS 1.5 sqmm | ₹40–₹60 |
| Shielded Twisted Pair (UL Listed) | ₹60–₹90 |
Note: Prices vary by brand, copper purity and ISI/UL certification.
The difference of ₹15–₹20 per meter is justified when compared to:
- False alarm service calls
- Device failure
- Loop rework
- Commissioning delays
- Safety non-compliance penalties
Installation Tips for Long-Term Reliability
- Keep minimum 300mm separation from power cables
- Avoid running loops near DG, HT, or HVAC ducts
- Use proper glands and ferrules
- Ensure metallic shielding is grounded through drain wire
- Test continuity and insulation after pulling
- Maintain maximum loop length as per panel specs
If you’re installing an addressable fire alarm system in India, follow this rule:
For Loop Wiring:
- Use Shielded Twisted Pair (STP) with FRLS insulation
- Minimum 1.5 sqmm copper conductor
- ISI/UL certified cable preferred
For Power & Sounder Circuits:
- Use FRLS or FRLSH cable
- Separate routing from loop cables
Both FRLS and Shielded Twisted Pair cables are used in fire alarm wiring, but their suitability depends on the system type, EMI conditions and loop length.
✅ FRLS is fine for small, conventional, or short-range systems.
✅ Shielded Twisted Pair (STP) is the best choice for addressable loops, especially in:
- Commercial towers
- Metro stations
- Industrial zones
- IT campuses
- Hospitals and hotels
- High EMI areas
With signal attenuation tests proving superior performance, STP ensures uninterrupted data transmission, regulatory compliance and life safety which is the ultimate goal of any fire protection system.
Read Also: Top 10 Common Programming Mistakes Engineers Make in GST Addressable Panels
Read Also: Can You Integrate GST Fire Alarm Panel with PLC / SCADA?
