Protective earth and neutral (PEN) conductors are the most common arrangement for low voltage (LV) electricity supplies. Occasionally PEN conductors break or pass abnormal currents to metalwork and equipment. This can mean they lose grounding and become dangerous.
However, there’s increasing concern about hazardous touch flow and diverted current faults from multiple causes. These can injure or even kill engineers who touch live metal casings and parts during electrical installation and maintenance.
Touch voltages and diverted currents
Touch voltages. A fault in the system can mean there’s no return path for current. For example, this can happen when there’s a broken or disconnected earth or neutral, combined with other faulty wiring. Metal parts such as distribution boards, boilers or control panels can then become dangerous.
Diverted current: Current may also flow through unintended paths such as earth or neutral conductors. While the circuit might appear to function normally, diverted current represents a serious risk.
Examples:
One. Current appears to flow correctly in a system but when measured it’s discovered current is flowing through earth conductors. Finding this problem requires measurements at multiple points across the earthing and neutral conductors. If undetected, disconnecting cables could break the return path, leading to a touch voltage hazard.
Two. Cross circuits or faulty wiring can mean current continues to flow in an isolated or dead circuit. Without careful checks, you could potentially break the return paths when disconnecting cables, creating dangerous touch voltages in the system.
Reducing risks
You can use a clamp meter to check current flow, especially if you have multiple cables connected to the same terminal. This can help minimise risks when disconnecting cables. However, safe isolation procedures may not specifically include tests for touch voltages and diverted current. As a result, you could overlook these hazards.
‘Test Before Touch’ is well-established for high-voltage equipment but can help reduce risks in all electrical installations. It could usefully apply before accessing or touching low-voltage equipment like distribution boards, control panels, pipework, and appliance casings. This could improve safety when working on parts of an installation that appear disconnected or dead.
Importantly, for PEN and similar faults all conductors may be at the same potential. Measurements using a standard two-pole voltage indicator may not effectively identify these risks.
Guidance on safe isolation and proving dead circuits may not sufficiently address these invisible risks. Including additional steps to identify touch voltages and diverted current could strengthen safe isolation procedures.
Please get in touch if you would like to discuss safe procedures for electrical installation and maintenance.
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