Main motor (main drive motor of a woodworking machine, chosen and wired so the cutter stops within the permitted run-down time)

01

The 10-second run-down rule and the machines allowed longer

University of Nottingham safety guidance, summarising HSE requirements, states that new woodworking machinery "must be equipped with an automatic brake that stops the tool in a sufficiently short time (10 seconds or less) if there is a risk of contact with the tool while it runs down", and that for existing machines the same standard is applied through PUWER and its Approved Code of Practice after a risk assessment, with deadlines from 2003 for circular saw benches to 2008 for all other machines. It lists braking as unnecessary where the run-down is already 10 seconds or less, and notes that large band re-saws or log saws may be allowed 35 seconds because of the energy to be dissipated. [3]

HSE's information sheet WIS38 adds that bringing some machines to rest within ten seconds "might be positively harmful to the machine and dangerous to the operator", allowing "35 seconds for some larger machines (30 seconds for bandsaws)"; the bandsaw figure differs from the 35 seconds Nottingham gives for band re-saws, so check the figure that applies to your machine. Braking need not be fitted where interlocked guards with guard locking enclose the cutters until they stop, or where the blade returns automatically to a safe position. [1] [3]

Give the motor or retrofit supplier the machine type and its existing motor (power, speed, frame, mounting inside or outside the frame, starter), the tool's inertia or measured run-down time, the target stopping time, the braking method wanted, the supply (single- or three-phase, reliability), E-stop and isolator arrangement, and the number of machines.

02

Braked motor, DC injection, variable speed drive or mechanical brake

WIS38 lists four ways to brake: replace the unbraked motor with a braked motor, fit a variable speed drive or a DC injection braking device to the existing motor, fit a power-operated mechanical brake, or fit a manual or foot-operated brake. Braked motors are "invariably longer" than unbraked ones, so space inside a machine frame and non-standard motor mountings can rule them out, and they are "not suitable for band re-saws" because of the stored energy. DC braking is not suitable for some motors, such as slip-ring motors; a VSD replaces the starter but a contactor may still be needed for emergency stopping, operated only after the motor has stopped, and high-inertia loads may need braking resistors. A mechanical brake should ideally be spring-applied and need power to release, and is "most efficient when applied to the low torque end of the drive unit". [1]

HSE's woodworking FAQ gives the cost of fitting DC braking as about £125 for parts plus £125 for electrical labour per motor, depending on motor size, and warns that switching off at the isolator cuts power to the braking unit before braking completes, which has caused run-down accidents; the E-stop should be used first, and the DC brake should be wired so that any local or remote E-stop applies it, with battery backup or an emergency supply considered where the mains is unreliable. [2]

03

Braking options compared

04

Woodworking main motor order details

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Machine: [type; tool; existing motor]
Motor: [power; speed; frame; mounting]
Stopping: [measured run-down; target time]
Braking: [braked motor; DC; VSD; mechanical]
Controls: [E-stop; isolator; contactor; supply]
Quantity: [machines]

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