Purpose

This safety bulletin alerts staff working on high-voltage (HV) metered or large low-voltage (LV) supplies using electronic meters about the risks of unintentional interconnection between auxiliary supplies and main metering voltage supplies.

Key Risk

An incident occurred where a staff member received an electric shock while working on a dead and isolated LVAC board.
Investigation revealed a floating voltage on the neutral bus bar due to a failed isolation within a meter, which created a path between the 110V voltage transformer (VT) supply and the LVAC network.
This was caused by either a manufacturing defect or meter failure.

Technical Findings

The HV meters on two 33kV Network Rail feeders were replaced in 2021 and required a separate auxiliary supply, which was incorrectly connected to the panel lighting circuit.
The neutral supply was switched (4-pole), so the voltage had no return path and floated on the neutral.

Standards & Recommendations

Integrated electronic devices (IEDs) such as meters, relays, and transducers must not use 240V auxiliary supplies.
Auxiliary supplies should be sourced from:
- 110V DC systems, or
- 110V AC centre-tapped transformers (as per ETS 05-1501 specification).
Any non-compliant setups should be reported via AIRLine and corrected through a work order.

Actions Required

Be alert to potential internal isolation failures in devices.
Ensure all meter and IED supplies comply with relevant standards.
Record any modifications on site drawings and apply appropriate warning labels.
Line managers must ensure staff are briefed within the specified timeframe (1 week marked as completed).

Contact

For further information, contact: Paul Austin – 07875 111 068