An LLNL employee received a mild electric shock when the employee placed a hand into water flowing from a laboratory faucet. The employee was not injured.
Responders initially attributed the shock to the significant presence of water on and around the sump pump, located adjacent to a drain-water holding tank installed in a metal-base cabinet (See Figure 1). The sump pump was not protected by a Ground Fault Circuit Interrupter (GFCI).
Further investigation revealed a faulty water-level sensing switch, positioned inside the drain-water holding tank, as the actual cause of the shock. The switch’s plastic cover had split open (see Figure 2), energizing the drain water in the plastic holding tank. When the employee turned on the water, it completed the circuit from the holding tank up to the faucet. The defective switch energized the water stream to 120 volts.
* It is preferable to wire control devices at reduced voltages (i.e., 12-48V), particularly where contact with liquids or corrosives is possible.
* The cause of the float switch housing failure was not determined. However, the float switch was not certified by a Nationally Recognized Testing Laboratory (NRTL), such as UL.
Recommended Actions for LLNL Employees
1. Have an electrician or qualified person inspect submerged switches in local sump-pump systems for cracks and, if necessary, replace them with NRTL-listed parts.
2. Evaluate control systems associated with liquids or corrosives. If line voltages are present on control devices, consider upgrading to low-voltage devices.
3. Use only NRTL-certified components, and observe manufacturers’ limitations and instructions.
4. Promptly notify the appropriate personnel of any plumbing leaks or the presence of excessive moisture. Although the water surrounding the sump pump was not a direct cause of this incident, water in or around any electrical equipment is inherently hazardous.