What Grenfell Tower Taught the Electrical Industry About Cable Specification

The 2017 fire was a cladding failure. But the way it spread raised uncomfortable questions about what "compliant" actually means in cable selection. The Grenfell Tower Inquiry, the coroner's report, and the subsequent regulatory response revealed a systemic weakness in how the electrical industry approaches fire performance in cable specification.

This article is not about blame. It is about what we learned and what we should be doing differently. Because the lesson from Grenfell is not just about cladding, or insulation, or building management. It is about the gap between "this cable meets the minimum standard" and "this cable is the right choice for this application."

Cable fire performance is classified under several interrelated standards, each testing a different aspect of fire behaviour:

• BS EN 60332-1 / IEC 60332-1 (Single cable vertical flame propagation): A single cable is exposed to a flame for a defined period. The test determines whether the flame self-extinguishes and how far the damage propagates along the cable. This is the minimum test that virtually all cables pass.
• BS EN 60332-3 / IEC 60332-3 (Bunched cable vertical flame propagation): Multiple cables are bundled on a ladder rack and exposed to fire. This test is far more demanding because cables in bundles behave differently — the combined fuel load and reduced heat dissipation mean fire can propagate along a cable bundle even when individual cables would self-extinguish. Categories A, B, C, and D represent increasing levels of cable density on the rack.
• BS EN 61034 / IEC 61034 (Smoke density): Measures the optical density of smoke produced by burning cables. Low-smoke cables are critical in evacuation routes where visibility determines survival time.
• BS EN 50267 / IEC 60754 (Halogen acid gas emission): Measures the acidity and quantity of corrosive gases released during combustion. PVC cables release hydrochloric acid (HCl) when they burn — this gas is toxic, corrosive to equipment, and reduces visibility.

The critical insight is that a cable can pass BS EN 60332-1 (single cable) and completely fail BS EN 60332-3 (bunched cable). In a riser shaft or service corridor where dozens of cables run together, the single-cable test result is almost meaningless. The bunched-cable test is what matters.

Here is the uncomfortable truth that Grenfell forced the industry to confront: for decades, the standard specification process for cables in high-rise buildings went something like this:

1. Determine the current rating requirement
2. Select a cable that meets the current rating from the standard tables
3. Verify voltage drop
4. Specify "to BS 5467" or "to BS 6724" on the schedule
5. Move on to the next circuit

Fire performance was treated as binary: the cable either had a British Standard number or it did not. If it had a number, it was "compliant." The question of whether that particular fire performance level was appropriate for that particular application was rarely asked with rigour.

In a single-storey warehouse, a standard PVC/SWA cable to BS 5467 is entirely adequate. In a 24-storey residential tower with a single staircase for evacuation, the same cable type in a riser shaft represents a fire engineering decision that should involve the fire engineer, the electrical designer, and the building control officer. That conversation rarely happened.

The post-Grenfell regulatory environment has changed this. The Building Safety Act 2022, the gateway process, and the updated Approved Document B all now require explicit consideration of cable fire performance as part of the fire strategy. Cable selection is no longer a purely electrical decision.

The lesson is clear: fire performance must be treated as a first-class parameter in cable selection, alongside current rating, voltage drop, and fault withstand. Here is what that means in practice:

• Building risk assessment first: Before selecting any cable, determine the building fire risk category. High-rise residential, care homes, hospitals, and buildings with sleeping accommodation require a fundamentally different approach to cable specification than commercial offices or industrial sheds.
• Route analysis: Identify which cable routes pass through escape routes, riser shafts, ceiling voids, and compartment boundaries. Cables in these locations need to be assessed for bunched-cable flame propagation (BS EN 60332-3), smoke density (BS EN 61034), and halogen acid gas emission (BS EN 50267).
• LSZH as the default for high-risk routes: Low-Smoke Zero-Halogen cables should be the default specification for any cable route that passes through or adjacent to escape routes in buildings with sleeping accommodation. The cost premium over standard PVC is typically 15–25%, which is trivial compared to the cost of a fire safety remediation programme.
• Fire-rated circuits: Circuits that must maintain function during a fire (emergency lighting, fire alarm, smoke ventilation, firefighter lifts) need cables tested to BS 8519 or BS EN 50200 for circuit integrity under fire conditions. These are not the same as LSZH cables — they are a separate and additional requirement.

Based on the lessons learned and the updated regulatory framework, every cable sizing exercise should now include these fire-related checks:

1. Is this a higher-risk building? (High-rise residential, care home, hospital, student accommodation, building with sleeping accommodation over 11 m)
2. Does this cable route pass through an escape route, riser shaft, or compartment boundary?
3. What is the cable density on this route? (If more than three cables in a group, consider BS EN 60332-3 Category A or B performance)
4. Is LSZH specified for all cables in high-risk routes?
5. Are fire-rated cables specified for life safety circuits? (Emergency lighting, fire alarm, smoke ventilation, firefighter services)
6. Has the fire engineer reviewed and approved the cable fire strategy?
7. Is the cable fire performance documented in the design report?

If any of these questions cannot be answered with confidence, the cable specification is incomplete — regardless of whether the current rating and voltage drop calculations are correct.

The electrical industry has responded to Grenfell in several concrete ways:

• BS 7671 Amendment 3 and Amendment 4: Updated wiring regulations with stronger references to fire performance requirements and explicit requirements for cable selection in higher-risk buildings.
• IET Code of Practice for Fire Safety: A new publication providing detailed guidance on cable selection for fire safety, including decision trees and worked examples for different building types.
• Manufacturer response: Major cable manufacturers (Prysmian, Nexans, Draka) have expanded their LSZH product ranges and improved fire performance documentation, making it easier for designers to specify the right cable for each application.
• CPD requirements: The IET, ECA, and JIB have all introduced mandatory fire safety CPD modules for registered electricians and electrical engineers.

These are positive steps. But they only work if individual engineers integrate fire performance into their daily cable sizing practice. A standard that nobody reads does not save lives. A fire performance check that nobody runs does not prevent fires.

When you run your next cable sizing calculation, take thirty seconds to ask: "Is this cable the right choice for this application, or just the cheapest one that passes the current rating test?" That question is Grenfell's lasting legacy for our profession.