Australian fire installers stand at an interesting crossroads. The familiar flat, “twin and earth” lead has served conventional detector loops for decades, yet today’s addressable panels behave more like data networks than simple switchboards. Choosing the wrong cable can introduce communication errors that surface only after ceiling tiles go back in place. This short guide unpacks the practical, technical and regulatory reasons why many professionals now reach for twisted pairs first.
Understanding the two profiles
A flat Thermoplastic-Sheathed (TPS) cable arranges its active cores side-by-side. That geometry is fine when the circuit merely carries a change in current – the principle behind legacy zone wiring. A twisted pair, on the other hand, keeps the conductors in constant rotation around each other. Because each wire spends equal time near external noise sources, unwanted voltages cancel out before they reach the panel’s differential receiver. It is a simple idea that still underpins Ethernet and high-speed audio leads, and it has become equally valuable inside fire systems that poll devices hundreds of times every minute.
Electromagnetic interference is no longer theoretical
Office towers hum with switch-mode power supplies, variable-speed drives and kilometres of power cabling. When a signalling line circuit (SLC) sits beside those services, induced voltages can scramble messages between smoke detectors and the panel. A single checksum failure forces the controller to retry the query; sustained interference prompts a “device missing” or “loop fault” warning that can take hours to trace. A Twisted TPS cable limits that risk by design, sparing technicians from costly call-backs.
Reading the standards
AS 1670.1 : 2018 treats every fire transmission path as a safety service. It asks for red sheathing, clear marking, and mechanical protection rated at least WSX1. It also distinguishes extra-low-voltage data paths from low-voltage speaker lines. That distinction explains why installers still stock three different red TPS rolls:
- Flat red TPS cables – common on conventional detector and bell circuits where EMI tolerance is generous.
- Flat red with white stripe TPS cables – mandated for EWIS and occupant warning speakers so maintenance crews can spot the 100-volt feed at a glance.
- The twisted alternative just described – now the default pick for SLCs, network buses and aspirating detector links.
Meeting the marking clauses is as important as electronic performance; a compliance inspector will reject a perfectly wired loop if the sheath lacks “ELV FIRE” every two metres.
Installation practicalities
Flat cable staples neatly against studs during first-fix work, and its shallow profile helps when multiple circuits share a narrow cavity. Yet retrofits seldom enjoy straight walls and open frames. Pulling a stiff flat cable through steel conduit full of elbows can shave its PVC or force kinks that later fail insulation tests. The round, more flexible twisted pair often threads complex routes with less effort.
Termination technique deserves equal attention. Untwisting more than about half an inch at the panel end erases the noise-cancelling advantage. A sharp side-cutting plier, a short strip, and immediate clamping into the screw terminal produce the best results. Where screened twisted cable is selected for MRI suites or heavy-industrial switch-rooms, bond the drain wire to earth at one end only to prevent ground loops.
Counting the dollars
Material price differences have narrowed. Wholesaler lists from mid-2024 show the gap between 1.5 mm² flat and twisted pairs at roughly ten cents per metre. On a typical 500-metre SLC, that equates to fifty dollars – less than an hour of senior technician time. If interference later causes a single false alarm on a Saturday evening, the overtime call-out instantly wipes out any saving. Future upgrades tell a similar story: a building cabled today with twisted loops can move to a faster protocol or cloud-monitored platform without rewiring, while a flat-cabled site faces invasive works and business disruption.
A quick decision matrix
| Circuit | System style | Recommended lead | Why |
| Detector zone (IDC) | Conventional | Flat red TPS | Analogue current change; EMI risk low. |
| Signalling line (SLC) | Addressable / network | Twisted TPS | Digital packets need noise rejection. |
| Notification appliances | Any | Flat red TPS | DC power; voltage drop dominates sizing. |
| EWIS speakers | Any EWIS | Flat red with white stripe TPS cables | Mandatory visual ID for LV audio. |
| Panel-to-panel bus | Networked | Twisted (screened if required) | High-speed data path. |
Looking ahead
With the National Broadband Network retiring copper telephone lines, even alarm monitoring now rides IP or cellular data. Fire panels increasingly push logs to cloud dashboards, and building managers expect remote diagnostics from a smartphone. Those features rely on the same clean signalling that keeps a smoke detector online. Installing twisted pairs today is less about chasing “state of the art” gadgets and more about laying a solid foundation for whatever arrives next.
Final thoughts for 2025 projects
Choosing cable is a small line item that safeguards the entire installation. For new work and major refurbishments, specify twisted pairs on every data circuit, keep the flat option for conventional zones, and never mix the two on the same loop. Mark and protect the run exactly as AS 1670 directs, and leave only minimal untwisted length at terminations. Take that approach and the cable tray will outlast several generations of panels, keeping occupants – and your reputation – safe for years to come.
