A surge protected extension lead failed resulting in it overheating and burning. Surveyors heard an audible ‘snap’ and then observed that three of their monitors had lost power. The vessel electrician was called to investigate and noted that a circuit breaker in the switchboard had tripped. The electrician reset the breaker, which was then followed by a distinct burning smell coming from a 4-way extension lead on the survey desk.
The extension lead was immediately isolated and removed. This equipment was the property of the third-party survey contractor.
What went wrong?
The extension cable was protected by an anti-surge system that relied on a fixed earth and varistors to allow passage of current to earth in the event of a power spike or surge. This design is to protect the equipment connected to the extension lead during very short power spikes, typically lightning strikes, not prolonged events where overheating could occur.
Vessels use residual current devices (RCDs). These devices effectively need to see balance on each phase and in the instance of a short on either phase, will trip the breaker/RCD. When the extension lead was connected to the ships power supply, the varistors heated up until one of the phases saw more or less current, thus tripping the breaker/RCD.
What actions were taken?
- Ensure all electrical extension leads are examined to confirm compatibility with vessel electrical system;
- Remove all unsafe items from use immediately.