Electrical Safety Guide for Vessels: How to Properly Operate Portable and Fixed Grounding Equipment?

In the ship's electrical system,Grounding and connecting to neutral are not only core technical measures for preventing electric shock accidents, but also form the basis of the practical assessment for marine electronic and electrical officers (ETO).Essential knowledge points in the exam.

Whether for routine maintenance or during operational assessments of shipboard power plants, mastering the correct usage protocols for grounding equipment is crucial. This article will provide an in-depth analysis of the “rules” and “taboos” of grounding operations.

I. Which electrical equipment must be grounded or bonded to neutral?

In accordance with the electrical safety requirements for ships, to prevent the hull from becoming energized due to insulation failure, the following metal parts must be reliably bonded:

1. Power Equipment Category: Motor, transformer, and high-voltage electrical apparatus bases and enclosures.Note: The motor grounding wire must be securely fastened to the dedicated grounding screw. Connecting it to the base is strictly prohibited.

2. Distribution Control Category: Metal frames for distribution cabinets, control panels, and operator consoles.

3. Cable System: The metal sheath of armored cable, junction box housing, and conduit.

4. Special Systems: Secondary windings of instrument transformers, generator neutral point cabinets, metal enclosures of electric heating equipment, etc.

ETO Practical Tips: Principles for Selecting Motor Ground Wire Cross-Section Area

• Phase line $S ≤ 25 mm²The cross-sectional area of the grounding wire is equal to that of the phase wire.

• Phase line $25 < S ≤ 50 mm² $: The cross-sectional area of the grounding wire is $25 mm²$。

• Phase line $S > 50 mm²$The cross-sectional area of the grounding wire is equal to that of the phase wire. $50\%$。

II. Exemption List: Under What Circumstances Is Grounding Not Required?

Under specific conditions, certain equipment may be exempt from grounding to simplify the system or for insulation considerations:

• Low-pressure equipment for dry environments: Communication $100V$ / DC $110V$ The following equipment enclosures.

• Excellent electrical conductivity shielding: Instrument and relay enclosures that are installed on a reliably grounded metal structure and have proper electrical connections.

• Insulated flooring: Low-voltage equipment in rooms with non-conductive flooring such as wood or asphalt (where maintenance personnel will not simultaneously touch the enclosure and a grounded object).

III. The Five Ironclad Rules for Portable Grounding Cable Operations“

When performing equipment maintenance, especially when using portable grounding wires (temporary grounding wires), the following safety procedures must be strictly adhered to. This is also a requirement for the assessment exam.Extremely prone to point deductionsThe segment:

1. Two-person work system: This procedure must be performed by two individuals: one to operate and one to monitor.

2. Protection in place: Operators must wearInsulated gloves, using dedicatedInsulating rod。

3. The order must not be reversed: * During installation: First connect the “ground terminal.” After verifying with a voltage tester that there is no voltage present, then install the “conductor terminal.”

   • During demolition: The sequence is completely reversed (disconnect the conductor end first, then the grounding end).

4. Connection Process: Must be securely connected.The use of the “wrapping method” is strictly prohibited.”Special clamps or bolts must be used.

5. Safety distance: During the process of connecting the grounding wire, the human body must not come into contact with the grounding wire or any ungrounded conductors.

IV. Common Mistakes to Avoid (Avoid Pitfalls Guide)

During the practical assessment conducted by the Maritime Safety Administration, examiners frequently observe the following details:

• Prohibited mixed wiring: In a three-phase four-wire low-voltage grid with a neutral point grounded, it is not permissible for some equipment to be connected to the neutral line while other equipment is only protected by grounding without being connected to the neutral line. This would allow fault voltages to propagate through the ground wire, posing greater hazards.

• Signal interference: DC signal grounding must be separated from AC signal grounding to prevent high-frequency interference from causing false operation of electronic instruments.

Conclusion

Proper use of grounding equipment is every shipboard electrical officer's lifesaver. Through standardized procedures, we can effectively prevent electric shock injuries, electrical fires, and equipment damage.