Reference
BS Numbers for Protective Devices
A quick reference to the British and harmonised standards behind the protective devices you specify every day, and why the number on the device decides which BS 7671 table applies.
Last reviewed
Every protective device is made to a standard, and that standard matters for design. It fixes the device's characteristics, so it decides the current that operates it in a given time, and therefore which maximum earth fault loop impedance and disconnection-time table you read in BS 7671. Get the standard wrong and the maximum Zs you check against is wrong too.
Fuses
| Standard | Device | Notes |
|---|---|---|
| BS 3036 | Semi-enclosed (rewireable) fuses | The old rewireable fuse. High fusing factor, so it needs a lower maximum Zs than a cartridge fuse of the same rating. |
| BS 88-2 | Cartridge fuses, industrial | HRC/HBC bolted or clip-in fuse-links for distribution and industrial use. |
| BS 88-3 | Cartridge fuses, domestic was BS 1361 | Consumer-unit and service cut-out fuse-links. Formerly BS 1361. |
| BS 1362 | Plug-top fuses | The cartridge fuse in a 13 A plug or fused connection unit. |
| BS EN 60269 | Low-voltage fuses (general) | The harmonised series that the BS 88 parts sit under. |
Circuit breakers
| Standard | Device | Notes |
|---|---|---|
| BS EN 60898 | Circuit breakers (MCBs) | Household and similar. Types B, C and D trip magnetically at 5, 10 and 20 times the rating. |
| BS EN 60947-2 | Circuit breakers, industrial | Industrial breakers and moulded-case circuit breakers (MCCBs), often adjustable. |
| BS 3871 | Miniature circuit breakers withdrawn | The earlier MCB standard, Types 1, 2 and 3. Still found in older boards. |
Residual current devices
| Standard | Device | Notes |
|---|---|---|
| BS EN 61008 | RCCBs | Residual current circuit breakers without integral overcurrent protection, the plain RCD. |
| BS EN 61009 | RCBOs | Residual current breakers with integral overcurrent protection. Trip on overcurrent to a B, C or D characteristic as well as on residual current. |
| BS 7288 | SRCDs | Socket-outlets and connection units incorporating RCD protection. |
| BS 7071 | PRCDs | Portable residual current devices, the plug-in adaptor type. |
| BS 4293 | RCCBs withdrawn | The earlier RCD standard, superseded by the BS EN 61008 / 61009 series. |
Arc fault, surge and switching
| Standard | Device | Notes |
|---|---|---|
| BS EN 62606 | AFDDs | Arc fault detection devices, for detecting series and parallel arcing faults. |
| BS EN 61643-11 | SPDs | Surge protective devices for low-voltage power systems. |
| BS EN 60947-3 | Switches & isolators | Switches, disconnectors, switch-disconnectors and fuse-combination units for isolation and switching. |
And the one that governs them all
| Standard | Document | Notes |
|---|---|---|
| BS 7671 | Requirements for Electrical Installations | The IET Wiring Regulations. Its disconnection-time and maximum Zs tables are indexed by the device standards above. |
Source & credit. This list is compiled with reference to Intrelec's own note, BS numbers for protective devices at intrelec.co.uk. Standards are revised and withdrawn over time, so always confirm the current designation and edition before relying on it.