Electrical Safety and Tag-Out in the Engine Room

What the rule requires

The shock numbers, and why they decide answers

The hazard is the magnitude of current through the body. About 1 mA is perceptible, roughly 10 mA produces the "can't let go" muscular freeze at the point of contact, and 100–200 mA through the chest causes ventricular fibrillation and death NEETS Mod. 1 §1-4. Stated the other way for the exam: a fatal shock can occur from 0.1 ampere, and voltages as low as 30 volts have been recorded as causing sufficient current to be fatal NEETS Module 1 Ch. 3 — Summary ¶2.

Body resistance is the limiting factor, and it is not a constant. Dry, intact skin may be 100,000 ohms or more; wet skin or a cut drops it to a few hundred ohms, which is why low voltages turn lethal in the damp, grounded space you work in . The shipboard 120-volt lighting circuit is very dangerous, not a nuisance voltage NAVEDTRA 14104 Ch. 12 — Precautions.

Securing a circuit before you work on it

Electrical and electronic circuits often have more than one source of power. Take the time to study the schematic or wiring diagram of the entire system to confirm every source is deactivated NEETS Module 4 §3.5.3. The regulation backs that up on the equipment itself: any cabinet, panel, box, or other enclosure containing more than one source of power must be fitted with a sign warning of the condition and identifying the circuits to be disconnected, and all electrical equipment and circuits must be clearly marked and identified 46 CFR §183.220.

All circuit breakers and switches from which power could possibly be supplied are secured — locked if possible — in the OPEN or OFF position and danger tagged NEETS Module 16 §1.5.5.

The tag itself does not isolate anything. The tag-out program exists to prevent improper operation of a component, equipment, or system that is isolated or in an abnormal condition, and the use of DANGER or CAUTION tags is not a substitute for other safety measures such as locking valves or pulling fuses. Tags indicate restrictions on operation, and are never used for identification purposes NAVEDTRA 14104 Ch. 1 — Equipment Tag-Out Program. Before maintenance, tag out and disconnect batteries or other sources of electrical power, which prevents both short circuits and accidental start-up NAVEDTRA 14104 Ch. 1 — Safety Program.

From the other side of the tag: do not touch or operate any device with a danger or caution tag attached without first contacting the EOOW . And when the job is finished, the tag is removed only by the same person who signed it when the work began .

Fuses and interlocks carry their own rules. Fuses are removed and replaced only after the circuit has been de-energized, using a fuse puller for cartridge fuses, and the replacement is the same type with the same current and voltage ratings. Interlocks, overload relays, and fuses are never altered or disconnected except for replacement, and never modified without specific authorization (same source). Never bypass an interlock unless authorized by the commanding officer, and then tag the bypass NEETS Module 19 Ch. 1 — Safety Observations for the Electrical and Electronics Technician.

The controller for a reefer compressor is fed from the main switchboard and also carries a control supply from a separate panel. You open and danger tag the main feeder breaker. Are you clear to open the enclosure and work?

No. Circuits frequently have more than one source of power, and every source must be deactivated — which is why the enclosure is required to carry a sign warning of multiple sources and identifying the circuits to be disconnected. Secure and tag the control supply as well, then prove the enclosure dead with an approved voltage indicator before working.

Energized work is the narrow exception

Repairs on energized circuits must not be made with the primary power applied except in an emergency, and then only after specific approval has been given by the commanding officer. Where that approval exists, keep one hand free at all times — behind you or in your pocket . Do not work on energized equipment unless absolutely necessary, never work alone, never receive an intentional shock, and never measure voltage in excess of 300 volts while holding the meter wire or probe .

The rest of the practice is unglamorous and heavily tested: one hand when turning switches on or off; switch and fuse box doors kept closed except when working inside; all metal objects off your person; clothing, hands, and feet dry; a rubber mat or other non-conductive material on top of a dry wooden platform or stool; insulated tools and molded insulated flashlights on exposed parts; and never a finger to test a hot line — use approved voltmeters or other voltage-indicating devices . No rings or metal watches .

Flammable vapours and hazardous locations

Do not start or operate electrical equipment when flammable vapours are present, and remember that a flame, spark, or lighted cigarette can cause a disastrous battery explosion — the electrolyte itself causes severe burns .

The construction rule follows the same logic. As far as practicable, electrical equipment must not be installed in lockers used to store paint, oil, turpentine, or other flammable or combustible liquid; where equipment such as lighting is necessary in those spaces it must be explosion-proof or intrinsically safe, meeting 46 CFR part 111, subpart 111.105 46 CFR §28.350. Note the order: the first requirement is to keep the equipment out, and explosion-proof construction is the fallback.

Installations in hazardous locations go in the least hazardous location practicable. Lighting circuits serving flameproof or explosion-proof fixtures in an enclosed hazardous space must have at least two lighting branch circuits, be arranged so there is light for relamping any de-energized circuit, must not have the switch and overcurrent device within the space, and the switch and overcurrent protective device must open all ungrounded conductors simultaneously 46 CFR §111.106-3.

On small passenger vessels the same objectives appear as performance requirements: the installation must minimize accidental personnel contact with energized parts and prevent electrical ignition of flammable vapours 46 CFR §183.200.

Grounding, enclosures, and outlets

Metallic enclosures and frames of electrical equipment must be grounded. A vessel with a nonmetallic hull must have a continuous, non-current-carrying grounding conductor tying together equipment enclosures and frames and connecting metallic items such as engines and fuel tanks to a common ground point, sized in accordance with section 250-95 of NFPA Standard 70. Aluminum must not be used for current-carrying parts of electrical equipment or wiring . On a portable tool or appliance cord, the green conductor is there to prevent shock to the operator if there is a short to the frame NEETS Module 4 §3.6 ¶1.

Receptacle outlets must have no exposed live parts with the plug opening uncovered, and a machinery space must have enough outlets that any location can be reached by a portable power cord no longer than 24 metres (75 feet) 46 CFR §111.79-1. Receptacles providing a grounded pole or a specific DC polarity must be configured so improper connection is not possible, and equipment must suit the roll, pitch, and vibration of the vessel underway . Combustible material should be avoided in the construction of electrical equipment 46 CFR §111.01-1.

General engine-room safety

Wear no jewelry or watches in machinery spaces, wear proper ear protection in all main machinery spaces, and do not perform maintenance work until the engine has been shut down and cooled. Do not attempt to operate equipment by overriding automatic shutdown or warning devices. Do not use oxygen to pressure test fuel lines and equipment. Take precautions against inhaling lacquer thinner, trichlorethylene, and similar solvent vapours. Keep oil from accumulating in the bilges, take care on an uneven keel that bilge water does not reach electrical machinery or wiring, and ensure safety guards are fitted at rotating and reciprocating equipment .

Keep loose tools, metal parts, and liquids from above electrical equipment, and never use steel wool or emery cloth on electric or electronic circuits . Do not use cable runs to hoist or support weight, do not use wireways for stowage, and do not go behind electrical switchboards .

For an electrical fire, use a CO2 extinguisher. For a shock casualty, remove the victim from the source of the shock, check for breathing, and give artificial ventilation if absent — CPR only if you are trained in its use — and obtain medical assistance as soon as possible . De-energize the source first, or free the victim with a non-conductor without touching them directly; electrical burns are often deep and worse than they appear .

Telling it apart

Waterproof against watertight

The criterion is how much moisture the enclosure may admit 46 CFR §110.15-1.

Watertight — enclosed so the equipment meets at least a NEMA 250 Type 4 or 4X, or an IEC 60529:2013 IP 56 rating. No allowance for ingress.
Waterproof — watertight, except that moisture within or leakage into the enclosure is allowed provided it does not interfere with operation of the equipment. For a generator or motor, leakage around the shaft is permitted if it is kept out of the oil reservoir and the enclosure drains automatically.
Most often misfiled: weather-exposed equipment. §28.350(a) accepts waterproof, watertight, or a watertight housing, so a waterproof motor showing a trace of shaft leakage is not automatically a defect 46 CFR §28.350.

Zone 0, Zone 1, Zone 2

The criterion is how much of the operating time an explosive gas or vapour mixture in air is present .

Zone 0 — continuously present, or present for long periods.
Zone 1 — likely to occur in normal operating conditions.
Zone 2 — not likely in normal operating conditions, or if it does occur, only for a short time.
Non-hazardous location — an explosive gas or dust atmosphere is not expected in quantities requiring special precautions for construction, installation, and use of electrical equipment.
Special Division 1 is the Class I, Zone 0 location in NFPA 70 Article 505 that may need extra consideration for the equipment installed in it.

Locations requiring an exceptional degree of protection

The criterion is exposure to weather, seas, splashing, pressure-directed liquids, or similar moisture conditions (same source).

Requires it — on deck, a machinery space, a cargo space, a galley or pantry area, a laundry, or a water closet containing a shower or bath.
Does not require it — an accommodation space, a dry store room, a passageway adjacent to quarters, a water closet without a shower or bath, and a radio, gyro and chart room.
The water closet appears on both lists. The shower or bath is the entire distinction.

Which list does the chart room fall on, and what does that get you?

The radio, gyro and chart room is a location not requiring an exceptional degree of protection, so the degree of protection called for by §111.01-9(c) or (d) applies rather than the exposed-location standard. It sits alongside accommodation spaces and dry store rooms, not alongside the machinery space.

Working a question

You are directed to overhaul the motor on the ship's service refrigeration compressor, fed from a panel in the machinery space.

Find every source. Study the schematic or wiring diagram of the whole system to confirm all power sources can be deactivated. If the enclosure carries a sign warning of more than one source of power, that sign already names the circuits you must disconnect 46 CFR §183.220.
Secure and lock. Every breaker and switch from which power could possibly be supplied goes to OPEN or OFF, locked where possible, and danger tagged NEETS Module 16 §1.5.5.
Isolate physically, not with paper. Pull the fuses — de-energized first, with a fuse puller — and disconnect the batteries or other power sources. The tag records the restriction; the lock and the pulled fuse do the isolating NAVEDTRA 14104 Ch. 1 — Equipment Tag-Out Program.
Prove it dead. Approved voltmeter or other voltage-indicating device, and treat the circuit as alive until it reads dead NEETS Module 4 §3.5.3.
Set yourself up. Metal objects off your person, hands and feet dry, rubber matting over a dry platform, insulated tools, molded insulated flashlight, one hand when operating switches.
If the job cannot be done dead, stop. Energized repair is emergency-only work requiring specific approval from the commanding officer, and it is done with one hand free; no reading above 300 volts is taken while holding the probe NEETS Module 19 Ch. 1 — Safety Observations for the Electrical and Electronics Technician.
Restore. Overload relays and interlocks go back exactly as found; a blown fuse is replaced with the same type and the same current and voltage ratings. The tag comes off only by the hand that signed it.

Where candidates lose the point

Answering that a 120-volt lighting circuit is not a serious shock hazard. Voltages as low as 30 volts have produced fatal current, and wet skin can drop body resistance from 100,000 ohms to a few hundred.
Reading the milliamp question loosely and choosing 10 mA for the fatal threshold. 10 mA is the "can't let go" freeze; fibrillation and death sit at 100–200 mA, and the summary figure is 0.1 ampere.
Treating one tagged breaker as isolation. The distractor is attractive because the tag looks like completion. Circuits commonly have more than one source of power, and the required warning sign on multi-source enclosures exists precisely because people stop at the first breaker.
Removing the tag because your work is done. Only the person who signed the tag removes it.
Choosing "when the repair requires it" for energized work. The trigger is emergency plus specific approval from the commanding officer — not operational convenience.
Upsizing a fuse that keeps blowing, or jumping an interlock to keep a machine running. Replacement fuses match type, current, and voltage rating; interlocks are bypassed only on the commanding officer's authority and the bypass is tagged.
Answering that a paint locker light must be explosion-proof, when the question asks what the rule requires first. As far as practicable, the equipment is not installed there at all; explosion-proof or intrinsically safe construction applies only where the equipment is necessary.
Placing the paint locker light switch inside the locker. The switch and overcurrent device must not be within a space containing explosion-proof or flameproof fixtures, and there must be at least two lighting branch circuits.
Reading "waterproof" as the stricter term. Watertight is the rating; waterproof tolerates leakage that does not interfere with operation.

Check yourself

You are told to renew a lighting fixture in the vessel's paint locker. What construction must the replacement have, and where does its switch and overcurrent device go?

Explosion-proof or intrinsically safe, meeting 46 CFR part 111, subpart 111.105. The switch and overcurrent device must not be located within the space, the space must be served by at least two lighting branch circuits arranged so there is light for relamping a de-energized circuit, and the protective device must open all ungrounded conductors simultaneously.

A shipmate is found gripping an energized cable and cannot release it. What is your first action?

De-energize the source, or free the victim with a non-conductor without touching them directly. Only then check breathing and pulse and begin artificial ventilation or CPR if trained. The grip itself is the 10 mA "can't let go" reaction — the current is still flowing, so touching the casualty puts you in the circuit.

The vessel has a fibreglass hull. What grounding arrangement is required, and how is the conductor sized?

A continuous, non-current-carrying grounding conductor connecting together the enclosures and frames of electrical equipment and connecting metallic items such as engines, fuel tanks, and equipment enclosures to a common ground point. It is sized in accordance with section 250-95 of NFPA Standard 70.

You find a valve carrying a CAUTION tag and need it in a different position to line up a system. What do you do?

Do not touch or operate it without first contacting the EOOW. That applies to any device carrying a danger or caution tag, regardless of which way you intend to move it.

A machinery space has receptacle outlets at both ends but the mid-space bilge area is 90 feet by cord from the nearest one. Is that acceptable?

No. There must be enough receptacle outlets throughout the machinery space that any location can be reached by a portable power cord not longer than 24 metres (75 feet).

An enclosure in a hazardous location is described as having a vapour-air mixture present only briefly during tank stripping and not during normal operation. Which zone, and why does the classification matter?

Zone 2 — the mixture is not likely to occur in normal operating conditions, or exists only for a short time if it does. The classification drives which construction and certification standard the installed equipment must meet, and installations in hazardous locations must in any case be sited in the least hazardous location practicable.

You must take running readings on a 480-volt motor controller that cannot be secured. What two limits apply before you put a probe in?

Energized work is done only when absolutely necessary, and repair with primary power applied requires specific approval from the commanding officer; with approval, one hand stays free. Second, you must not measure voltage in excess of 300 volts while holding the meter wire or probe — the leads are clipped on with the power off, before the reading.