Ground Works
Electrical Dewatering-Pump PTW & LOTO Isolation
Isolate an electrical dewatering pump safely under a controlling permit — energy source identification, standby resilience, lock-out execution, voltage proving, try-start verification and controlled return to service.
v2.1Updated 9 Aug 2026ADOSH-SF v4.1 (February 2026)Learning Objectives
- Explain why a pump isolation is a linked isolation certificate under a controlling PTW, not a stand-alone authority to work.
- Identify every credible energy source on a dewatering pump installation.
- Confirm dewatering resilience before isolating a duty pump.
- Execute lock-out, stored-energy release, voltage proving and try-start verification in the correct order.
- Maintain the energy-control condition across shift change and changed conditions.
- Return the pump to service and close the isolation certificate and PTW correctly.
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1. Governing Principle
A dewatering-pump isolation is normally a linked electrical isolation certificate under a controlling PTW. ADOSH-SF CoP 21.0 requires the Authorized Person (AP) to verify implemented isolations before authorising the permit, to attach isolation certificates to the PTW and isolation register, and requires the Permit Holder to confirm the workplace is safe to start work. CoP 24.0 requires a written energy-control procedure wherever unexpected energisation, start-up or release of stored energy can cause harm. Where the isolating device can be locked, use lockout — a tag alone is a warning device, not a physical restraint.
2. The Dewatering No-Go
Never isolate a duty pump where doing so can create uncontrolled water rise, flooding, base heave, piping, uplift or an access/egress hazard. Before isolation you must have an independently powered, tested standby pump and an engineer-accepted contingency arrangement — or stop and reassess the work. The dewatering supervisor must confirm the isolation will not breach groundwater, water-level, flooding, discharge or stability trigger limits.
3. Planning Checklist Before Isolation
The controlling PTW names the exact pump, location, scope, duration, Permit Holder, AP, competent electrician and work party. The isolation certificate is raised, cross-referenced and registered. Pump ID, feeder number, MCC/DB panel, breaker/isolator, local isolator, control circuit, voltage and cable route are positively identified from the current single-line diagram and site labels. Duty/standby plan, emergency power, fuel, discharge route and high-water alarm are proven functional. All affected personnel are notified in a commonly understood language. The area is dry, lit, safely accessible with no exposed energised parts and a maintained rescue route. The electrician holds current authorisation, correct PPE, insulated tools and an approved voltage indicator. Where the pump sits in a deep or constrained excavation, atmospheric testing and confined-space controls apply.
4. Energy Sources to Identify
Normal feeder; generator/ATS source; UPS or control power; remote PLC/SCADA command; float switch; pressure switch; automatic restart; VFD; capacitor bank; residual mechanical rotation; and pipeline or water pressure. Missing any one of these is the most common cause of an unexpected start during dewatering work.
5. Isolation and LOTO Execution
Stop the pump on its normal control and record water level, runtime/flow and duty/standby status. Disable all local, remote and automatic start signals including floats, SCADA, timers, auto-restart and ATS transfer logic. Open the identified primary energy-isolating device — a control push-button, HMI, VFD stop or selector switch is never the energy isolation. Isolate control power and all alternate supplies. Apply the AP's or authorised electrician's lock and identification tag to each isolating device, legible in a wet environment. For multiple workers use a group lockbox or multi-lock hasp so every exposed worker applies their own personal lock. Release or restrain stored energy: allow VFD/capacitors to discharge per the manufacturer, verify rotation has stopped, restrain water pressure and backflow. Prove the voltage indicator on a known live source, test for absence of voltage phase-to-phase and phase-to-earth, then re-prove the tester. Perform a controlled try-start from every credible command point with people clear. Record isolation points, lock/tag numbers, verification result, instrument ID, time and signatures. The AP then verifies the isolation, the Permit Holder confirms the area is safe, and only then is the PTW authorised.
6. Controls During the Work
The PTW, isolation certificate and LOTO diagram are displayed at the work location with a duplicate live permit at the central control point. No person bypasses, removes or transfers a lock or tag without the written authorised procedure and the controlling AP. The dewatering supervisor monitors water level, standby-pump performance, power, fuel and weather throughout. If the water level rises, the standby pump fails, a groundwater trigger is reached or the scope changes — stop work and refer the permit back to the AP. At shift change, preserve the energy-control condition, carry out a documented transfer of isolation and locks, revalidate the PTW and brief the incoming party.
7. Return to Service and Close-out
The electrician and Permit Holder verify work is complete, tools and temporary leads removed, guards and covers restored, terminals secure and the area clean and dry. Confirm all personnel are clear with a head count where relevant and notify affected persons of re-energisation. Each authorised worker removes only their own lock and tag; exceptional removal follows the written emergency/absence procedure with documented authority — never informally. Restore supplies in the approved sequence, enabling control, remote and automatic functions only when safe. Test the pump under controlled conditions: rotation direction, electrical readings, flow, discharge route, high-water alarm, duty/standby changeover and generator/ATS response. Record post-restoration water level, pump condition and test results. The AP closes the isolation certificate and controlling PTW only once normal readiness is restored.
Knowledge Assessment
1. An electrical isolation certificate for a dewatering pump is:
2. Under CoP 24.0, where the isolating device can be locked you must:
3. Before isolating a duty pump you must confirm:
4. Which of these is a valid energy isolation point?
5. Correct voltage-proving sequence is:
6. A 'try-start' verification means:
7. For multiple workers on one isolation, the correct arrangement is:
8. If the water level rises during the isolation, the crew should:
9. Who may remove a personal lock in normal circumstances?
10. The AP may close the controlling PTW only after:
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