Isolation and proving dead on a starter panel

Why hands-on work needs a dead panel

A wire lifted or a part pulled on a live panel puts your hands on 220 or 440 V.

Without a lock and tag anyone can switch Q1 back on while your probes or hands are in the panel.

Q1 off and locked does not prove the panel dead: a back-feed, a second supply or a welded pole can keep it live.

Hands-on work only on a panel proven dead: isolate, lock and tag, live – dead – live.

Isolation step by step

1. Isolation, first line: inform the watchkeeper and the ECR, before the work and before the test run.
2. Work on the panel under a permit to work, as the ship’s SMS requires.
3. Operating and isolation instruction: before work on the panel or the motor, S1 OFF, Q1 OFF, padlock and tag on Q1, then prove dead with a proved meter (live – dead – live).
4. Q1 isolates the panel below it. To work on Q1 itself, isolate upstream at the group panel.

Live – dead – live

Live – dead – live. Prove the meter on the proving unit, test for dead at the place of work, prove the meter again.

A meter that has failed shows 0 V on a live circuit. Without proving the meter, "dead" proves nothing.

Prove the meter, test every supply conductor (the control pair and six power readings), prove the meter again.

On board, prove dead with a two-pole voltage detector (EN 61243-3) or a test lamp, not a multimeter that can be left on the wrong range (HSE HSG85 ¶54, GS38 ¶19).

Traps when testing for dead

Trusting the "voltage on L3" under load: it is back-fed through the motor windings.

START released: KM1 A1 reads tens of volts on 10 MΩ. The coil is open, so A1 floats and picks up a ghost voltage; LoZ shows 0.

Ω on X3:3–X3:4 with the panel dead: a healthy K11 is de-energised too, so its contact is open and proves nothing. The AMS loop on X3 is not isolated by Q1.

Ohms, megger and the meter jacks

On a live circuit the ohmmeter reads nonsense, and the leads are on live metal for nothing: until the circuit is proven dead, the meter is a voltmeter.

Voltage present: never megger a live circuit.

The test leads go where the meter probes are: LINE on the red, EARTH on the black. Only on a circuit proven dead; disconnect electronics from it first, discharge after the test.

The 500 V test voltage can damage electronic timer relays, the HMI sensors or the LED lamps, and the reading through them is false.

Red lead in VΩ for voltage; move it to A only to measure current in series, then back.

With the lead in the A jack the meter is almost a short circuit: across a voltage it blows the meter fuse or flashes over.

Live readings

Live readings at 440 V are on the permit to work (COSWP §20.13.8): second engineer in attendance, dry insulating mat, insulated gloves, no jewellery.

Letting it run on while you fault-find: at 0.3 bar/min the HP safety valve lifts in about 2 minutes. Stop it first, or right after one quick reading.

Before you switch back on

Switching on with a wire lifted leaves a live loose end in the panel and a circuit that is not as drawn.

A fuse above the drawing rating no longer protects the cable and the device: the next fault burns wiring instead of blowing the fuse.

Land every lifted wire and fit every part, then remove lock and tag and switch Q1 on.