Ungrounded Short Discovery in Process Technology HTX Series Heater [Update]

Image for Ungrounded Short Discovery in Process Technology HTX Series Heater [Update]

Type:  Just-In-Time Report

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

Published As:  Public


Topics:  Electrical, Contracts and Procurement, Maintenance, Hazardous Energy Control


An unexpected discovery of exposed hazardous energy occurred during scaffold installation when a worker's socket wrench made contact between a piece of scaffolding (which was grounded) and the housing of an immersion heater on the sump of a scrubber assembly. The contact resulted in a spark, an audible pop, and the tripping of the power supply breaker.

The investigation determined three causes for the exposed hazardous energy:

1.The heater unit, although installed per the manufactures directions, was not bonded to ground. The assembly includes two power leads and a ground lead. The provided ground lead is bonded to the heater element only. The heater element is electrically isolated from the housing. The installation instructions do not advise the installation of a grounding bond to the heater housing; which is required to make the installation National Electric Code compliant.

2.Inside the heater housing, a thermostat copper capillary tube made contact between one energized power supply terminal and the heater housing, shorting power (280 VAC) to the housing. During consultation, the manufacturer, Process Technology, stated that the copper capillary tube should have been sleeved with insulation to prevent this kind of short. The short, in combination with the lack of proper grounding, resulted in the exposure of hazardous energy.

3.The heater assembly was procured as a Quality Level 3 General Service item and required inspection and testing by the Electrical Authority Having Jurisdiction upon receipt since it was a Non-Nationally Recognized Testing Laboratory listed item. This receipt inspection did not occur, rather the heater assemblies (3) were accepted and placed in the spare parts inventory and subsequently installed in the plant.

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