Instruments & Safety Systems

1. Megger — Torque as a Test Instrument

At an intermediate megohm reading, voltage and current torques balance. The motor insulation criterion stated here is at least 1 MΩ.

Hand-cranked (armature in permanent field) or battery-electronic, a megger pits voltage torque against current torque on one pointer: open circuit swings full to infinity, dead short drags it to zero.

Ritual: prove the meter shorted, ground both terminals separately to prove earths, then probe conductors — below minimum, high-voltage machinery stays off. Multimeters cannot substitute: 3 V tickles insulation that 500 V DC breaks down, and only the breakdown voltage tells the truth.

2. Thermocouple — Heat Into Microvolts

Three thermoelectric effects sit behind every thermocouple:

Seebeck

Welded dissimilar wires develop volts across a temperature gradient.

Peltier

Push current instead and junctions heat or cool.

Thomson

Current along a gradient absorbs or releases heat.

Tables turn microvolts back into degrees:

3. Earth Faults — Alarm, Then Hunt

Fault

A phase touching neutral (earthed plant) or hull potential (insulated plant).

Leakage

Capacitive or high-resistance bleed is mere leakage — not yet a fault.

Trace it live by elimination — open and close breakers carefully (mind essential loads) until the alarm clears, starting where faults breed: galley and laundry first.

Insulated neutrals

Survive first faults at equal potential (alarm only).

Earthed neutrals

Pass fault amps that trip gear instead — which is exactly why HV plants earth: one fault must kill the circuit, not smoulder into two.

One transformer subtlety: the 220 V distribution board needs its own earth lamps — the step-down air gap means 440 V lamps cannot see a 220 V earth.

4. Detectors & the Flicker Trap

Smoke

• Ionization chambers feel flaming ions first.
• Optical heads see smouldering scatter first.
• Dual heads cover both.

Heat

• Fixed-temperature eutectic links melt at their set point.
• Rate-of-rise heads fire on climb speed.

Warning — Stroboscopic aliasing.

Freezes or reverses rotating machinery under single-phase flicker. Defeat it with full three-phase lighting or high-frequency drivers, never with warnings alone.

5. Ex Family — Four Ways to Deny an Ignition

Intrinsic safety in practice means Zener clamps or galvanic isolators on every wire entering the hazardous area — the barrier, not the device, guarantees the energy ceiling.

6. Battery Room — Hydrogen Sets the Rules

A lead-acid bank uses 2 V cells; twelve in series provide 24 V. For battery work, wear an apron, gloves and a face shield against acid splashes.

Gas discipline

Ventilate continuously, never smoke or bring naked lights near, and fit spark-proof lighting — hydrogen needs only a spark to remind you it was there.

Terminal discipline

Never bridge positive to negative — the flashover is violent. Disconnect negative first, reconnect it last.

Upkeep rhythm

Weekly cell voltages and hydrometer specific gravity, terminals greased against corrosion, occasional load tests, cells kept covered (distilled water top-up), batteries dry, clean, trickle-held, terminals smeared.

7. Shock — Limits, Precautions and Rescue

• Normal safe voltage: 50 V
• Fatal AC or DC: 15 mA
• Rescue now vs 3 min late: 70% → 20%

Safe voltage normally sits at 50 V, shifting with body resistance and path — insulating boots or a mat raise the survivable line. Shock as low as 15 mA AC or DC can kill. And the welding paradox resolves in one phrase: the whole hull sits at the same potential, so with no potential difference across the body there is no shock — even beside kilovolt ignition gear that must break down an air gap to throw its spark.

Before touching anything electrical: switch off power, wear protective clothing and safety shoes, hang the no-switch board, stand on a rubber mat, strip off rings and bracelets, use insulated tools, prove dead with a voltmeter — and prove the voltmeter itself on a known supply. Keep one equipped person standing by, inform authority, and hold a proper work permit.

1. Raise the alarm — shout it before you touch anything.

2. Isolate the current — switch off. If impossible, drag or push the victim clear with something non-conductive, never bare hands on victim or source.

3. Resuscitate at once — if breathing is feeble or stopped, begin artificial respiration immediately and check heartbeat and pulse. Started at once, ~70% recover; three minutes late, ~20%.

Warning — Confined air kills silently too.

Never enter a space breathing 19% oxygen or below — test the air, ventilate, and follow enclosed-space entry discipline before any rescue inside.

8. Barriers, Hull Current & Last-Resort Power

Intrinsic safety keeps hazardous-area energy below ignition — Zener clamps or galvanic isolators on every wire in (walkie-talkies live here). ICCP makes the whole hull a cathode: transformer-rectifier current flows off graphite/silicon-iron/platinised-titanium anodes through seawater onto steel, steered by a passive reference cell, auto or manual — fewer, harder-driven anodes than any sacrificial scheme. Fuses melt once per pole with high rupture capacity and I²t limiting, seated in holders or isolators (see the 32/125 A switch-fuses).

Emergency generation: battery plus hydraulic/pneumatic starts (two independent means always), weekly unloaded battery runs, monthly hydraulic starts with automatic changeover proved on load. Load-sharing fault? Dropping set is not developing power — governor or over-tight speed droop, diagnosed before the healthy set inherits the ship.