Selection Guide · 10 min read · Updated 2026-10-12
Fire Resistant vs Flame Retardant Cable: They Are Not The Same Thing
One property is about what a cable does to a fire and the other is about what a fire does to a circuit. A flame-retardant cable stops a flame travelling along it; a fire-resistant cable keeps carrying its load while it is being burned. Confusing them produces a very common specification error: a life-safety circuit wired in LSZH cable that is neither fire resistant nor required to be, or one that goes dead at the moment it is needed. This article sets out both tests, the classes, and the circuits where each genuinely applies.
Two different questions, two different tests
A flame-retardant cable is tested to see whether it propagates fire. A sample is exposed to a flame and the extent of the charred length after the flame is removed is measured, and the cable passes if the damage stops within the stated limit. The cable itself is allowed to be destroyed; the question is only whether it takes the fire with it.
A fire-resistant cable is tested to see whether the circuit survives. A sample is mounted in a furnace, energised at its rated voltage and loaded with its rated current, and the test measures whether the circuit still conducts at the end of it. Nothing about the cable's appearance matters; the pass criterion is purely electrical. The two tests are on different properties and they are commissioned for different reasons, and a cable that is excellent at one can fail the other outright.
- Flame retardant: limits the spread of fire; the test measures charred length
- Fire resistant: maintains circuit integrity; the test measures whether the circuit still conducts
- Low smoke zero halogen is a third property again, and it is not either of these
- A fire-resistant circuit also has to survive its supports, its fixings and its joints, not just its cable
Flame retardant: what the IEC 60332 tests measure
The single cable test, IEC 60332-1-2, applies a defined flame to one vertical sample for a set time and requires the damage to stop short of the top. It is a screening test, and passing it is the minimum expected of a modern cable in almost any building.
The bunched tests of IEC 60332-3 are much harder, because a bundle of cables behaves very differently from one: each cable in the bundle is heated by its neighbours and the fire loads are higher. The categories are graded by how much combustible material is in the sample, so a specification has to say which one applies. This is the test that matters in a riser, a plant room or a cable tunnel, where hundreds of cables share one route.
| Category | Non-metallic volume per metre | Flame application | Where it is specified |
|---|---|---|---|
| A F/R | 7 litres per metre | 40 minutes | The highest requirement, where the authority demands it |
| A | 7 litres per metre | 40 minutes | Heavy concentrations of cable in one route |
| B | 3.5 litres per metre | 40 minutes | Risers, plant rooms, tunnels |
| C | 1.5 litres per metre | 20 minutes | The common commercial grade for building wiring |
| D | 0.5 litres per metre | 20 minutes | Small cross-sections in limited volumes |
Fire resistant: what circuit integrity means
Circuit integrity means that during the test the cable continues to carry the voltage and the current it was rated for. The test rig energises the sample and monitors it continuously, and the failure criteria are electrical: the conductors shorting to each other or to earth, or the circuit opening so that the load is no longer supplied. A fire-resistant cable can be reduced to a blackened reel at the end of the test and still pass, as long as the circuit held.
The universal construction is a fire barrier over the conductor, and the test standards differ mainly in how hot they are, how long they run, and what else they throw at the cable. The three names you will meet are BS 6387, EN 50200 and IEC 60331, and the differences between them are real enough that a specification has to name one.
| Standard | Flame temperature and duration | What it can also include |
|---|---|---|
| BS 6387 | C: 950 °C for 3 hours; W: 650 °C; Z: 950 °C | Water spray in the W test and mechanical shock in the Z test, giving CWZ |
| EN 50200 | At least 830 °C, with classes PH15, PH30, PH60, PH90 and PH120 | Supplementary water spray and mechanical shock tests in the BS 8434 series |
| IEC 60331-21 | At least 750 °C, commonly 90 minutes | A separate water spray option exists in the IEC 60331 series |
BS 6387 and the C, W and Z categories
BS 6387 is the British standard and it is written as three independent categories that are combined. Category C is flame alone: the sample is exposed to a flame at 950 °C for three hours and must maintain integrity throughout. Category W adds water: the cable is burned, then sprayed with water while the flame continues, to reproduce what a sprinkler or a fire brigade hose does to a burning cable. Category Z adds mechanical shock: the sample is hammered on an anvil during the fire, which reproduces falling debris and structural collapse.
A cable described as CWZ has passed all three, and that is the shape most UK life-safety specifications take because it is the most demanding combination. A cable described only as C has passed the fire alone and may not survive the water or the shock, which in a real fire is precisely what it will meet. When a consultant writes BS 6387 without a category, the requirement is incomplete, and the cheapest cable that passes C alone satisfies it.
EN 50200 PH classes, and the water and shock options
EN 50200 takes a different approach and expresses the result as a duration. The test flame is at least 830 °C and the classes are PH15, PH30, PH60, PH90 and PH120, the number being the minutes of fire plus the 15 minutes of the cooling period that follows it. A PH120 cable has survived two hours of fire and then the period that follows, which is why PH120 is the class normally asked for on smoke extract and fire lift circuits.
EN 50200 on its own is a fire-alone test. The water spray and mechanical shock additions sit in the BS 8434 series, and a specification that wants the equivalent of BS 6387 CWZ under the European standards has to name them as well. In practice this is the wording most commonly used: a cable to EN 50200 PH120, with the supplementary water and shock tests of BS 8434. The duration chosen should come from the evacuation and fire-fighting strategy for the building, not from habit.
How a fire-resistant cable is built: the mica barrier
There is no exotic chemistry involved. Between the conductor and the insulation, a fire-resistant cable carries a lapped tape of mica bonded to a glass cloth carrier. When the polymeric insulation and sheath burn away, the mica remains: it is a mineral that stays intact and electrically insulating at temperatures well above anything a building fire reaches, so the conductors stay separated and the circuit keeps working. The duration and the severity of the rating come from how many layers of tape are applied and how it is lapped.
Two practical consequences follow. The mica tape makes the cable larger, stiffer and more expensive, with a bigger minimum bending radius and a higher material cost that is unavoidable. And the barrier has to be continuous through the joints and terminations: a fire-resistant cable terminated in a standard accessory has a weak point at the accessory, because the mica tape ends where the termination begins. Jointing and terminating fire-resistant cable is a specialist task for the same reason.
Which circuits actually require it
The rule that decides it is simple: a circuit needs a fire-resistant cable if it has to keep working during a fire, and nothing else does. General power, general lighting and comfort ventilation do not, and specifying fire-resistant cable for them is money spent where it buys nothing. The circuits that do appear in every standard: fire alarm systems where the detectors, sounders or the panel have to survive the fire; emergency lighting, at least the part supplied from a central system; fire pumps and sprinkler pumps; smoke extract fans; fire-fighting lifts; and emergency voice communication.
There is one requirement that is easy to miss. The circuit is a system, and the cable is one part of it: BS 8519 covers the selection and installation of fire survival cables for smoke and heat exhaust systems and makes the point that the fixings and supports have to survive too. A cable that holds together while the tray it sits in collapses and pulls the termination apart has not maintained the circuit. Cable supports for these systems are usually specified as fire resistant as well.
| Circuit | Requirement | Typical class or grade |
|---|---|---|
| Fire alarm circuits that must survive the fire | Fire resistant | BS 6387 CWZ, or EN 50200 PH30 for standard systems and PH120 for enhanced systems |
| Emergency lighting from a central battery | Fire resistant | Commonly PH30 to PH120 depending on the evacuation strategy |
| Sprinkler and fire pump supply | Fire resistant | Commonly PH60 or PH120, and follow the pump standard |
| Smoke extract and heat exhaust fans | Fire resistant, with fire-resistant supports | Commonly PH120 per BS 8519 |
| Fire-fighting lift | Fire resistant | Commonly PH120 |
| General power and lighting | Flame retardant, not fire resistant | IEC 60332-1 or the appropriate 60332-3 category |
| Comfort ventilation and plant | Flame retardant | IEC 60332-1 or 60332-3 |
Specification errors and the wording for an order
The errors below appear in RFQs repeatedly, and each of them is cheap to avoid and expensive to discover. The first is the one that gives this article its title, and it runs in both directions: a fire-resistant cable where flame retardance was all that was needed, and a flame-retardant or LSZH cable on a circuit that has to survive.
- Specifying LSZH and assuming it also provides fire resistance: it does not, and this is the most common error in the industry
- Writing fire resistant without a standard, a category and a duration, so the cheapest C-only cable satisfies the requirement
- Specifying the cable but not the supports, the fixings or the jointing method, so the circuit fails at the accessory
- Asking for fire resistance on every circuit in the building, which multiplies the cable cost for no safety benefit
- Using fire-resistant cable but standard terminations, which leaves an unprotected gap at the end of the mica barrier
- Forgetting that the cable must also be low smoke when it is inside an occupied escape route
Frequently asked questions
What is the difference between fire resistant and flame retardant cable?
Flame retardant cable resists the spread of fire along its length and is tested for charred length under IEC 60332. Fire resistant cable maintains circuit integrity while burning, and is tested by energising the cable in a furnace and checking that the circuit still conducts. One protects the building from the cable; the other protects the circuit from the fire.
Is LSZH cable fire resistant?
No. LSZH describes the smoke and acid gas a cable gives off, which are evacuation and corrosion hazards. It says nothing about whether the circuit keeps working. A circuit that must operate during a fire needs a mica tape fire barrier, and where the cable is also in an escape route the two properties are combined in one product.
What does BS 6387 CWZ mean?
It is three categories combined. C is flame alone at 950 °C for three hours, W is 650 °C with a water spray to simulate sprinklers or fire brigade hoses, and Z is 950 °C with mechanical shock to simulate falling debris. A cable marked CWZ has passed all three, which is why UK life-safety specifications often ask for it by name.
What is a PH120 cable?
It is an EN 50200 classification, where the number is the minutes of fire resistance plus the following cooling period. PH120 means the cable maintained circuit integrity for 120 minutes at a flame temperature of at least 830 °C. The class range is PH15, PH30, PH60, PH90 and PH120, and the duration should follow the evacuation and fire-fighting strategy for the building.
Do I need fire-resistant cable for emergency lighting?
For centrally supplied emergency lighting, yes, because the luminaires have to operate while the fire is in progress. Self-contained luminaires with their own batteries do not need it to the same extent, because the battery is at the fitting. The duration is set by the evacuation strategy, commonly 30, 60 or 120 minutes, and it should be written into the specification with the standard.
Need this worked out for a specific installation?
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