Date: July 6, 2005
Identifier: 2005-RL-HNF-0023
Lessons Learned Summary:
A construction Electrician received an electrical shock while terminating a white neutral wire to a relocated electrical panel in Building 234-5Z. Improper circuit modification and a lack of quality control to identify the as-built mis-configuration, resulted in power being supplied to a device by a panel other than the one on which work was being performed, which had been locked out and zero energy verified.
Discussion of Activities:
On Thursday May 12, 2005 an electrician received an electrical shock while terminating a white neutral wire to a relocated electrical panel in Building 234-5Z. The electrician sensed a slight tingling through his leather gloves. The Electrician immediately made the hot neutral safe and began trying to find the source of the problem. The electrical shock event was not made known to the work supervisor for several minutes (after the supervisor reported discovery of the wiring problem). The Electrician was taken to First Aid, examined, and released for full return to work.
Voltage did not show in the zero energy check because the neutral wire created a complete circuit while spliced through the neutral bus. A potential to ground would show only after the neutral was de-terminated. The Electrician's hand completed the circuit to ground as he was preparing to splice the wire into the new panel.
The energized neutral came from an unidentified 120-volt circuit. Neutral wires are not normally labeled, but the electrical work team believed the neutral wire to have been de-energized because it was within the hazardous energy electrical boundary. The PFP Electrical Team had walked down the circuits to this panel extensively (about a half-dozen times) and believed all the circuits had been positively identified. After the event, the neutral was found to belong with a security circuit in a different panel and was moved to the correct panel.
Analysis: The shock was caused by an open neutral (grounded) conductor that was carrying a load. Although hazards caused by open neutrals in a multi-wire branch circuit (also known as an Edison circuit) are well known to electricians, this incident did not involve such a circuit. An improper circuit modification was performed sometime in the past that resulted in power being supplied to a device by a panel other than the one on which work was being performed, which had been locked out and zero energy verified. That would not have been a problem except that the modification left the neutral conductor for the circuit in the existing panel that was being relocated. Since a voltage check of the neutral conductor (that caused the shock) with any of the ungrounded conductors in the panel being relocated would not indicate a live circuit, there was little that could have been done to prevent this. There was no reason to suspect anything that would have suggested testing all neutral conductors to ground, which might have been the case had it been known that an improper modification had been performed. This incident should serve as a reminder of the hazards of open neutral conductors. A voltage check of an open neutral to ground would be advisable if a multi-wire branch circuit is suspected, or if working in a panel or enclosure (e.g., auxiliary wire way) where multiple sources of power may be present.
Recommended actions: Electricians should be made aware that historic installations of non-code compliant wiring may be present in their facilities. Pre-job planning of work in a panel affected by a moved circuit, should include the expectation that a neutral wire may go hot when cut.
The Job Hazard Analysis electrical safety checklist should include that a neutral wire may go hot when cut, voltage rated PPE should be worn when cutting a neutral wire, and a zero energy check should be made before and after the wire is cut.
A voltage check of an open neutral to ground would be advisable if a multi-wire branch circuit is suspected, or if working in a panel or enclosure (e.g., auxiliary wire way) where multiple sources of power may be present.
Estimated Savings/Cost Avoidance: Not determined
Priority Descriptor: YELLOW/Caution
Work / Function: Configuration Management
Hanford-Defined Category: N/A
Hazard(s): Electrical/NEC
ISM Core Function(s): Analyze Hazards and Implement Controls
Originator: Fluor Hanford, Inc. Submitted by Nancy Zeuge
Contact: Project Hanford Lessons Learned Coordinator; (509) 372-2166; FAX 372-3950; e-mail: PHMC_Lessons_Learned@rl.gov
Authorized Derivative Classifier: Not required
Reviewing Official: Gerald Whitney
Keywords: Electrical Safety, Conduct of Operations - Lockout/Tagout (Electrical), Conduct of Operations - Inadequate Job Planning (Electrical), OSHA Reportable/Industrial Hygiene - Electrical Shock
References: Occurrence report: RL--PHMC-PFP-2005-0011
