Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
IEC 60332-3-21: Bunched Cable Flame Test — Fire Safety for High-Rise Building Shaft Cables
Single-Wire Flame Retardancy ≠ Bunched Cable Flame Retardancy
IEC 60332-3-21:2018 specifies bunched cable vertical flame propagation test methods. A cable passing IEC 60332-1 single-wire flame testing does not guarantee bunched flame retardancy — because multiple burning cables mutually reinforce heat output, producing higher flame temperatures and faster propagation.
| Test | Specimen | Ignition | Criterion |
|---|---|---|---|
| IEC 60332-1 | Single wire (60 cm) | 1 kW gas burner | Char height ≤50 mm from upper clamp |
| IEC 60332-3 Cat A | Bunched (7 L/m combustible) | 20 kW ribbon burner | Char height ≤2.5 m |
| IEC 60332-3 Cat B/C | Bunched (3.5/1.5 L/m) | 20 kW | Char height ≤2.5 m |
The bunched cable test uses 20× the ignition power of the single-wire test — this is not over-testing, but simulating real fire scenarios where multiple cables burn simultaneously in a building shaft.
TNLab — Passing single-wire flame testing does not mean passing bunched testing. Cable fires in high-rise shafts are among the deadliest electrical fires.
