Ungrounded Short Discovery in Process Technology HTX Series Heater

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Type:  Just-In-Time Report

Publisher:  CH2MHill Plateau Remediation Company, Hanford Site (CHPRC)


Topics:  Electrical, Maintenance, Hazardous Energy Control

An arc that resulted from the inadvertent contact between a ratchet and the casing outlet box (part of a Process Technology HTX Series immersion heater assembly) led to the discovery of uncontrolled hazardous energy. The immersion heater was used to maintain sump temperatures on a Sludge Stabilization Chemical Scrubber tank.
The investigation has identified a manufacturing error: the uninsulated copper thermostat sensing line was in contact with both the power terminal and the case body. This allowed the case body to become energized. In addition, the grounding wire provided in the assembly was not bonded to the casing and therefore did not ground out the entire unit. The ground provided by the manufacturer would only result in grounding the unit if the heating element itself were to be compromised. The lack of case grounding prevented the circuit breaker from tripping, thus potentially exposing workers to an uncontrolled hazardous energy source.

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