Machine Wiring & VSD Commissioning SWMS

Machine wiring and variable speed drive commissioning is high risk construction work in New South Wales because the commissioning phase cannot be done dead. Wiring can be. Proving direction of rotation, tuning a drive to its motor, verifying a safety circuit and running the machine under load cannot — and section 291 of the Work Health and Safety Regulation 2025 (NSW) captures that under the energised electrical category, with a safe work method statement required under section 299. SafeWork NSW is the regulator. AS/NZS 3000 governs the installation and AS 4024 governs the machine's safety of machinery requirements.

A variable speed drive breaks the trade's oldest rule of thumb: that isolation makes equipment safe to touch. It does not, and the reason is the DC bus. The drive's capacitors hold a lethal charge for minutes after the supply is opened, and the display that would tell you the bus is still live is itself powered from that bus — so **the darkest, deadest-looking drive is the least reliable indication you will ever be offered**. The manufacturer's discharge time is waited out, and then the bus is proved at the terminals with an instrument. Every time.

The drive's second trap is that it starts things. Auto-restart on power return is a factory default on many drives, and a permanent magnet motor generates voltage at its own terminals whenever its shaft turns — which means restraining a conveyor or a fan against windmilling is an electrical control, not a mechanical convenience. This SWMS is authored around those mechanisms: DC bus discharge and proving, isolation that includes the start path and the shaft, and safety-circuit verification that is proved by test rather than assumed from a parameter list.

Hazards identified

14 hazards covered, sorted by priority.

Control measures

Hierarchy-of-controls order: elimination → substitution → isolation → engineering → administrative → PPE.

1. 1Isolate the supply, then wait the manufacturer's full DC bus discharge time and **prove the bus dead at the terminals with an instrument** — never rely on a dark display, which is powered from the very bus it would warn you about.
2. 2Isolate and lock out the supply AND every start path — the run command, the remote and PLC start, and any auto-restart parameter — because killing the run command is not isolation of a machine designed to restart, and verify rotation is impossible physically rather than from a panel.
3. 3Obtain an arc flash risk assessment establishing incident energy and approach boundaries at the actual switchboard and drive panel, verify upstream protection, and close the panel for any test that can be done closed.
4. 4Complete all wiring and pre-energisation verification dead under Part 4.7 Div 4 ss.154 & 157; identify the commissioning tasks that genuinely require energisation in advance and carry them out under a documented method with a competent person and a second person present who can isolate and perform rescue.
5. 5Restrain the shaft of any permanent magnet motor before work — a PM motor generates voltage at its own terminals whenever the shaft turns, so shaft restraint is an electrical control, not a mechanical convenience.
6. 6Fit and secure all guards for every running test, with an emergency stop reachable from the working position and proved before the first run, and exclude persons from the machine's motion envelope during any run.
7. 7Isolate and dissipate every stored energy source in the driven machine — hydraulic accumulators, pneumatic receivers, suspended masses, springs and flywheels — and block or restrain what cannot be dissipated.
8. 8Provide a designed working platform or EWP for tray, wiring and panel installation above floor level, with rated anchorage and a rescue plan before any harness use.
9. 9Prove every safety function by test at the machine — a safety circuit is verified by demonstrating it stops the machine on demand, never by reading a parameter list or a drawing — and reverse and re-verify any temporary bypass before handover.
10. 10Treat the heatsink, braking resistor and motor casing as hot for a defined period after any run rather than testing by touch, and guard or barrier hot surfaces in the work area.
11. 11Verify termination torque to specification, ventilation clearances and filter condition before energisation, and thermographically survey the panel under load at commissioning.
12. 12Assess noise exposure against the exposure standard by a competent person, limit and rotate time at running machines, and select hearing protection to the measured level to AS/NZS 1270.
13. 13Deburr and grommet gland plates and cut edges, use the correct stripping tools, and wear eye protection and cut-resistant gloves for panel building and cable preparation.
14. 14Use mechanical aids and two-person handling for drives, panels, motors and cable drums, stage material at the point of use, and rotate tasks in restricted plant space.

Applicable Codes of Practice

High-Risk Construction Work triggered

Worked example

An electrician is called back to a conveyor drive that tripped overnight. He opens the isolator, waits what feels like long enough, and opens the drive's terminal cover to check the motor terminations. The drive's display is dark — it has been dark since he pulled the isolator, which is exactly what he expected. He touches a DC bus terminal and receives a fatal shock. The investigation finds the drive was a 90 kW unit with a bus discharge time of five minutes stated on a label inside the door and on page one of the manual. Ninety seconds elapsed between isolation and contact. The display was dark not because the bus was discharged but because the display is powered from the bus through a low-current supply that drops out long before the bus reaches a safe voltage — the darkness was the first symptom of a bus that still held lethal energy, not evidence that it did not. The contractor's SWMS said: isolate, lock out, test for dead. It did not say how long to wait, and it did not say to prove the bus at the terminals. Both facts were available in the manufacturer's documentation on the day. SafeWork NSW's position was that the SWMS did not address the hazard the equipment actually presented, and the PCBU could not show that the worker had been given the information the drive's own manual provided. This SWMS names the mechanism, requires the manufacturer's discharge time to be waited out, and requires the bus proved dead at the terminals before contact.

Related legislation

• Work Health and Safety Act 2011 (NSW) — primary duty of care (s19), consultation (s47), notifiable incidents (ss35–38), industrial manslaughter (s26A)
• Work Health and Safety Regulation 2025 (NSW) — HRCW (s291), SWMS content and requirement (s299), SWMS review (s302)
• Work Health and Safety Regulation 2025 (NSW) — Part 4.7 Division 4, sections 154 and 157 — prohibition on energised electrical work
• Work Health and Safety Regulation 2025 (NSW) — Chapter 5 (plant) — guarding, isolation and stored energy in the driven machine
• Electricity Supply Act 1995 (NSW) and the licensing framework administered by NSW Fair Trading — electrical work licensing

Frequently asked questions