Cases & enclosures BRANCHING OUT W
hen it comes to safeguarding large buildings against the risk of fire, electrical circuits often include centralised overcurrent protection
upstream. Typically installed with the main distribution equipment, devices like circuit breakers can secure entire groups of outgoing circuits. However, to ensure the safety of concentrations of people in large building complexes, branch-level protection can be required.
In these types of buildings, ranging from railways stations to football stadia, devices like fire alarms, smoke extraction systems, or emergency lighting need segregated branches to prevent a failure in one area of the circuit taking out the power to the whole system. The challenge, though, comes at the fuse; while fuses enable isolation and prevent a break of connection impacting the wider circuit, they can fail prematurely due to heat. In the event of a fire, when the device or system they’re connected to is relying on them most, their protection is essential.
PROTECTING THE FUSE
Fire-rated systems require the simplest, most stable designs. Fewer components reduce the potential for failure during extreme heat, minimising weak points. Moreover, reducing connections means less complexity in certification and testing. By maintaining circuit breakers and fuses at a centralised point, electrical junctions need only protect straight-through connections. In these situations, while fire-protection enclosures are still required, providing between 30 and 120 minutes’ protection in the event of a fire, the housings need to protect only the terminal blocks and cable junctions. However, when branch-level protection and circuit isolation is required for fire safety design providing between 30 and 90 minutes’ protection with devices and systems protected by decentralised fuses, this requires a specially designed enclosure. It’s not just that the enclosure needs to have a larger volume, but adding fuses turns a fire-rated enclosure from a passive housing component into an active protection device. During a fire, heat can impact how the
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fuse reacts, so the enclosure must be able to resist temperatures and ensure conditions that maintain it, as well as protecting the terminal connections from degradation.
REAL-WORLD APPLICATIONS
The requirement for branch-level fire protection can apply to any large building that relies on life-safety systems where failure during a fire is unacceptable. Typical settings include football stadia and sporting venues; arenas and entertainment halls; as well as hotels and residential blocks, including prisons. Common requirements also include transport hubs, such as airports, as well as bus, coach and railway stations.
To protect an electrical circuit from fire at a railway station, an enclosure must also provide pressure suction resistance. Spelsberg’s WKE 6T fire-protection enclosure, which can also accommodate fuses for branch connections, is pressure and suction-tight according to the Gotthard guideline. Named after the Gotthard Base Tunnel, the world’s longest and deepest railway tunnel, the requirements mean equipment
TUNNEL-TESTED
As a result, the WKE 6T enclosure has been tested to ensure that its housing, seals, cable entries and cover remain intact and maintain their protective function when exposed to pressure loads. This prevents the enclosure from drawing in smoke, hot gases, or contaminants, or facing damage caused by pressure fluctuations. This testing is also in addition to the enclosure’s IP66 rating, signifying that the housing is dust-tight and can also withstand high-pressure water jets, common during firefighting. Pressure-testing also makes the enclosure well suited to use in rail, road and pedestrian tunnels, in addition to railway station applications. Alongside the WKE 6T, Spelsberg’s Rapidbox enclosure enables the fast installation of cable taps and sockets from an existing power cable in tunnel applications without needing to cut the supply cable. Compared to installing a new cable, this approach saves significant time. Also providing up to 90 minutes’ fire protection as part of the WKE
FIRE-SAFETY ENCLOSURES FOR FUSE-PROTECTED CIRCUITS
For fire protection in large buildings such as railway stations, branch-level circuits are required to ensure that critical safety systems remain operational even if part of a system fails. However, introducing local fusing increases design complexity and thermal challenges, and the enclosures that protect these junctions require specialist fire-rated testing. Chris Lloyd, managing director at Spelsberg UK, explains.
must withstand rapid pressure changes caused by events such as passing high-speed trains.
AV: General power supply, SV: Safety power supply August 2026 Instrumentation Monthly
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