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Open any fire protection submittal for cable containment and four letters do more work than they should: F1, F2, F3, F4. Tender documents specify them, suppliers quote them, and on too many projects nobody involved can state what the class actually tested — which coating thickness, which steel gauge, which support spacing. Fire resistance rating F1 F2 F3 F4 cable tray meaning is therefore not a vocabulary question. It is a question of what evidence sits behind the letter, and that evidence decides whether the drawing survives the fire consultant's review.
This guide fixes the definitions first, then works through the two thickness numbers that make a class verifiable, and closes with the decisions to make before the drawing is issued. If you are still separating the vocabulary itself, start with our article on fire rated versus fireproof cable tray; this one assumes that much is settled, and works with the numbers LIWEIJU verifies batch by batch on production orders.
1. Fire resistance rating F1 F2 F3 F4 cable tray meaning
The grading comes from GB 29415-2013, and it measures time, not quality tiers. The standard grades fire-resistant cable tray systems by how long the cables inside stay energised in a standard fire test:
✅ F4 — circuit integrity for at least 30 minutes
✅ F3 — at least 45 minutes
✅ F2 — at least 60 minutes
✅ F1 — at least 90 minutes
Three conditions in that definition matter more than the letter itself. First, the specimen is the complete assembly: tray, cover, coating or lining, splice plates and supports, tested together. Second, the acceptance criterion is circuit integrity — the cables keep working while the cold-face temperature rise stays within 180 °C. Third, the assembly must carry its rated load in the fire condition, not less than 2.0 kN/m uniformly distributed — a much harder test than at room temperature.
Internationally the same idea travels under other names: DIN 4102-12 in Europe tests functional maintainability for E30 to E90 durations, BS 476-20/21 and IEC 60331 define related fire-resistance test methods, and UL 2196 governs the US market. When a class letter is quoted on a cable tray for an export project, ask which test method and laboratory stand behind it, because a rating without a named standard is a marketing word. Jiangsu Liweiju Electrical Co., Ltd. grades systems to GB 29415 and quotes the tested assembly configuration alongside every class, so the letter arrives with its evidence attached.
✅ Bottom line: F1 to F4 are durations measured on the complete tested assembly. The letter means nothing without the standard, the laboratory and the tested configuration behind it.
2. Intumescent coating thickness required for 60 minute fire rating
Coating thickness is the first number that makes a class verifiable, because duration is bought with dry film thickness. The ranges typically quoted against GB 29415 grading on a steel substrate are:
✅ F3 (45 minutes) — 1.4 to 1.6 mm dry film
✅ F2 (60 minutes) — 1.8 to 2.0 mm dry film
✅ F1 (90 minutes and above) — 2.4 to 2.6 mm dry film
The intumescent coating thickness required for 60 minute fire rating therefore sits at 1.8 to 2.0 mm, and a supplier who quotes a duration without a thickness has told you nothing you can check. At 200 to 250 °C the coating reacts and expands ten to thirty times into a carbonaceous char, and that char — not the steel — is what slows heat transfer into the cable. Whether a class is real reduces to whether this number was measured on the delivered batch, which is why LIWEIJU quotes thickness and duration in the same line of the quotation. Ask for a dry film thickness record with each production lot, and check it at cut edges and bolt holes, where thin spots start.
One substrate note for overseas buyers: on hot-dip galvanized tray, the coating needs a primer compatible with zinc. Skip it and adhesion fails within two to three years, starting at the edges — the test report number then no longer describes the tray on site.
3. Fire resistant cable tray sheet thickness for 90 minutes
Coating is only half of the thickness story. Specifying fire resistant cable tray sheet thickness for 90 minutes means checking the steel gauge beneath the coating, because the steel does the load-bearing while the char does the insulating. Above 450 to 500 °C, mild steel loses close to half its yield strength; a 0.8 mm side rail that carries 2.0 kN/m at 20 °C may sag between supports at 60 minutes, and a sagging route drags on its supports no matter how good the coating is.
In practice, the gauges we see behind F-class results run from 1.0 mm for short-span routes serving light circuits up to 1.5 to 2.0 mm for 90-minute routes carrying the full 2.0 kN/m, with support spacing held at or below the tested span — commonly 1.5 to 2.0 m. The check that matters: the sheet gauge, alloy and support spacing in the type test report must match what the factory ships. A test on a 2.0 mm rail does not transfer to a 1.0 mm supply lot, and that substitution is the most common way a real class becomes a paper class.
LIWEIJU issues both records with F-class orders — coating DFT per batch and steel sheet gauge per lot — so the two numbers on site can be reconciled against the certificate. For OEM projects the same profile runs in multiple gauges on one line, and custom widths from 100 to 800 mm are available in bulk.
✅ Bottom line: Verifiable thickness is two numbers — coating dry film and steel gauge — and both must match the tested specimen, not just the brochure.
4. Which class does the drawing actually need?
Match the class to the circuit schedule, not to the building. The durations we see specified across hospital, metro, commercial and industrial work:
✅ Fire alarm loops — 30 to 60 minutes → F4 or F3
✅ Emergency lighting — 60 to 90 minutes → F2
✅ Fire pump and sprinkler supply — 90 to 120 minutes → F1 territory
✅ Smoke extraction fans, firefighter lifts — 120 minutes → F1
✅ Hospital critical supply — 120 to 180 minutes → F1 with margin confirmed by the fire engineer
Over-specification is a real cost, not a conservative habit. Moving a large route from F2 to F1 adds roughly 0.6 mm of coating over every metre, and on a metro or hospital project that becomes a serious line item for protection the circuit may never need. Fix the schedule before tendering; changing the class after purchase means re-testing records and re-quoting the route.
Frequently asked questions
Q: Is F1 always the safe choice?
A: No. The fire resistance rating f1 f2 f3 f4 cable tray meaning is a duration on a tested assembly, and F1 on every route is how budgets get rejected. Evacuation-oriented circuits sit comfortably at F3 or F2; only circuits that must run during firefighting justify 90 minutes and above. The class is an engineering input, not a quality badge.
Q: Are F1–F4 recognised outside China?
A: The durations map naturally to the E30–E90 classes tested under DIN 4102-12, and the underlying physics is the same, but the letters themselves are not a global certificate. For export projects, specify the test method and laboratory alongside the class, and keep the tested assembly drawing in the submittal package.
Q: What documents should come with an F-class order?
A: Three things. A type test report that names the complete assembly — gauge, coating, supports, spacing — not just the tray. A dry film thickness record for the delivered batch. And a primer compatibility statement if the substrate is galvanized. Any supplier of fire resistant cable tray who cannot produce all three is selling a letter, not a rating. LIWEIJU issues all three with every F-class order as standard.
Next step
Send us your circuit schedule and we will mark which class each route genuinely needs, which thickness pairs with it, and where the current specification is buying duration nobody asked for. No charge, no obligation. LIWEIJU is a fire rated cable tray manufacturer in China supplying OEM and custom F-class systems from 100 to 800 mm width, with ISO 9001 production control, batch DFT records and third-party verification available on request for wholesale orders. Reach the factory through the LIWEIJU contact page with your schedule, destination port and target classes for a quotation, or browse the fire resistant cable tray product range first.
www.lwjelec.com
Jiangsu Liweiju Electrical Co., Ltd.
