Containment and Support Systems

Overview

Containment and support systems for fire alarm cabling are not just a matter of neatness or workmanship. They are a critical part of maintaining circuit integrity during fire conditions.

A fire-resisting cable is only as effective as the way it is:

supported
routed
protected
segregated
jointed

BS 5839-1:2025 makes it clear that unless cables remain supported for a duration similar to that for which the cable itself can survive fire, early circuit failure can occur due to strain on terminations caused by collapsing cables. The standard also notes that collapsed cables can create a serious entanglement hazard for firefighters.

Why Containment and Support Matter

Containment and support systems serve several purposes:

maintaining cable support during fire
reducing the risk of mechanical damage
assisting segregation from other services
reducing electromagnetic interference
improving maintainability and fault-finding
protecting circuits at vulnerable routes and penetrations

In practice, good containment and support design is part of the overall fire performance of the installation, not an optional finishing detail.

Core BS 5839-1:2025 Requirements

Directly Fixed Cables

BS 5839-1:2025 says cables fixed directly to surfaces should be:

neatly run
securely fixed
fixed at suitable intervals in accordance with the cable manufacturer’s recommendations

It also states that cables should not rely on suspended ceilings for support.

Non-Combustible Support

Methods of cable support should be:

non-combustible
such that the circuit integrity is not reduced below that afforded by the cable itself
capable of withstanding a similar temperature and duration to that of the cable

The commentary makes clear that this effectively rules out things like:

plastic cable clips as the sole means of support
plastic cable ties as the sole means of support
non-metallic trunking as the sole means of support where cable survival in fire is needed

This is one of the most important practical points in the standard.

Typical Forms of Containment

Cable Tray

Cable tray is commonly used where:

multiple circuits are run together
long horizontal routes are required
mechanical protection is needed
future additions are likely

BS 5839-1:2025 notes that tray may be used as a form of mechanical protection. However, tray alone is not enough unless the method of cable support remains compliant and maintains circuit integrity in fire.

Conduit

Conduit is often used where:

additional mechanical protection is required
routes pass through vulnerable areas
a neat enclosed installation is required

Where conduit is used to satisfy the recommendations for mechanical protection, BS 5839-1:2025 says it should conform to the relevant part of BS EN 61386.

Trunking

Trunking can assist with:

route control
segregation
physical protection
orderly installation

Where fire alarm cables share common trunking with other services, a compartment separated by a strong, rigid and continuous partition should be reserved solely for the fire alarm cables. Any non-metallic trunking used in the system should conform to BS EN 50085-1.

Ducting

Ducting may be used in some routes for mechanical protection or route segregation, particularly in harsher environments. As with all containment, it needs to be considered in terms of support, protection, and long-term maintainability. BS 5839-1:2025 includes ducting among the examples of means of providing mechanical protection.

Support Systems in Fire Conditions

What the Standard Is Getting At

A cable may survive the thermal conditions of a fire, but still fail if the support system collapses first and puts strain on the terminations.

That is why BS 5839-1:2025 requires support methods to be non-combustible and fire-resilient, rather than simply “tidy” or “adequate under normal conditions”.

Practical Implications

In practice, this means:

metal fixings are generally expected
tray supports, cleats and fixings need to remain serviceable in fire
plastic-only support arrangements are not suitable as the sole means of support
cables should not be draped loose above ceilings or across voids

Mechanical Protection

BS 5839-1:2025 says that where cables are used with no additional mechanical protection, they should be:

MICC to BS EN 60702-1 and BS EN 60702-2, or
SWA cables conforming to BS 7846

If the cable does not conform to one of those standards, it should be given mechanical protection wherever:

physical damage is likely
rodent attack is likely

Mechanical protection should also be provided in all areas less than 2 m above floor level, except in relatively benign environments such as offices and shops where cables are clipped directly to robust construction. In particularly arduous conditions, such as impact from forklift trucks or goods trolleys, mechanical protection should be provided to all cables.

Jointing and Junction Boxes

BS 5839-1:2025 says cables should be installed without external joints wherever practicable.

Where joints are necessary:

terminations and accessories should minimize the probability of early failure in fire
terminals used for jointing, other than those inside system components, should be made of materials able to withstand a similar temperature and duration to the cable
all joints outside system components should be enclosed in junction boxes
those junction boxes should be labelled “FIRE ALARM”

The standard gives metal components with ceramic terminal blocks as an example of suitable terminals.

Segregation from Other Services

Fire alarm cables should not be installed within the same conduit as cables of other services. Where trunking is shared, fire alarm cables should have their own compartment separated by a strong, rigid, continuous partition.

BS 5839-1:2025 also says that manufacturer recommendations should be followed regarding separation of fire alarm cables from the cables of other services in order to avoid electromagnetic interference.

Where fire alarm cables carry power in excess of ELV, they should be segregated from ELV fire alarm circuits and the mains supply cable to any control, indicating or power supply equipment should not enter through the same cable entry as ELV cables. Within equipment, LV and ELV cables should be kept separate as far as practicable.

Capacity of New Containment

Where new conduit, trunking or tray is installed, BS 5839-1:2025 says its capacity should be in accordance with BS 7671:2018+A3.

This matters because overloaded containment can cause:

cable damage
poor heat dissipation
poor maintainability
difficulty with future additions or replacements

Wall Penetrations

External Walls

Where a cable passes through an external wall, BS 5839-1:2025 says it should be contained in a smooth-bore sleeve of metal or other non-hygroscopic material sealed into the wall.

The sleeve should:

slope downwards towards the outside
be plugged with a suitable non-hardening waterproof compound

This is to prevent the entry of:

rain
dust
vermin

Internal Walls

Where a cable passes through an internal wall, a small clearance hole should be provided. If additional mechanical protection is needed, a smooth-bore sleeve should be sealed into the wall.

The commentary in Clause 35 also states that penetrations need to be made good to avoid the free passage of fire or smoke.

Separation from Lightning Protection Systems

BS 5839-1:2025 says that all metallic parts of the installation, including:

conduit
trunking
ducting
cabling
enclosures

should be separated from any metalwork forming part of a lightning protection system.

This is an often-missed issue in real buildings, especially on rooftops, plant areas and external riser routes.

Common Field Issues

Plastic Fixings Used as Sole Support

This is one of the most common issues on site.

Examples:

plastic clips directly to wall
plastic ties under tray
non-metallic trunking relied on as the only support

BS 5839-1:2025 commentary makes clear these are not appropriate as the sole means of support where cables need to remain supported in fire.

Cables Resting on Ceiling Tiles

Still common in refurb jobs and rushed installations.

This is not acceptable, the standard explicitly says cables should not rely on suspended ceilings for support.

No Mechanical Protection at Low Level

A lot of installations use standard fire alarm cable clipped direct down walls in vulnerable circulation or service areas.

BS 5839-1:2025 says protection should generally be provided below 2 m above floor level, except in relatively benign environments.

Shared Conduit with Other Services

A bad but still-seen shortcut.

The standard says fire alarm cables should not be installed in the same conduit as other services.

Poor Segregation in Shared Trunking

Another common issue is running fire alarm and other service cables loose in the same trunking compartment.

BS 5839-1:2025 requires a dedicated compartment separated by a strong, rigid and continuous partition.

Unsupported Joints Above Ceilings or in Voids

Random connector blocks or unlabelled junctions in voids are a regular field problem.

The standard expects:

external joints only where practicable
appropriate fire-resilient terminals
enclosed junction boxes
boxes labelled FIRE ALARM

Containment Too Close to Lightning Protection Conductors

On external routes, rooftop plant, and some façade runs, metallic containment is sometimes installed hard against LPS metalwork.

BS 5839-1:2025 says metallic parts of the installation should be separated from lightning protection system metalwork.

Practical Guidance

When assessing containment and support systems for a fire alarm installation, check:

Are cables properly supported by non-combustible means?
Are they independent of suspended ceilings?
Is mechanical protection provided where damage is likely?
Are low-level runs properly protected?
Is shared trunking properly partitioned?
Is conduit/trunking compliant with the relevant standards?
Are joints minimized, enclosed and labelled?
Are wall penetrations properly sleeved and sealed?
Is separation from other services and lightning protection adequate?
Is the containment sized properly for the installed cables?

Summary

Containment and support systems are a core part of fire alarm circuit integrity, not just a cable management issue.

Under BS 5839-1:2025, compliant installation means:

neat and secure fixing
non-combustible support
no reliance on suspended ceilings
correct segregation from other services
mechanical protection where required
compliant conduit/trunking systems
properly enclosed and labelled joints
correct treatment of penetrations
separation from lightning protection metalwork

A fire-resisting cable installed on poor containment or weak supports is still a poor installation.