Electrical Forensics Investigation Supports Root Cause Determination Following Rooftop Busway Explosions

Overview

Envista Forensics was engaged following separate rooftop busway explosions at two large public transit operations facilities. The facility was under construction as part of a major transportation infrastructure initiative designed to support battery-electric bus charging operations and emergency command functions.

The newly constructed operations center incorporated multiple rooftop electrical busway runs designed to distribute power from the utility vault to electrical rooms throughout the site. After two catastrophic failures occurred within a short period, the owner de-energized the rooftop busway system and initiated a forensic engineering investigation to determine the cause of the losses.

Envista’s electrical forensic engineers worked with the project’s electrical contractor to evaluate the failures, assess installation and environmental conditions, and provide an independent engineering opinion regarding the cause of the incidents.

The Challenge

The failures occurred within outdoor ABB ReliaGear busway systems installed on the rooftop of one of the facilities. The first incident occurred after personnel identified a power loss to one of the facility's switchboards. Investigation at the site revealed significant damage to an elbow connection.

A second explosion occurred the following week, involving another busway, resulting in another power loss event, accompanied by smoke and an audible explosion from the rooftop system.

The project team faced several complex technical questions, including whether the failures stemmed from manufacturing defects, installation practices, environmental exposure, or system design conditions. The rooftop environment, combined with the system’s weather exposure and the project’s critical electrical infrastructure, required a detailed forensic evaluation to identify the underlying failure mechanism and determine whether additional systems remained at risk.

Our Approach

Envista conducted a comprehensive forensic engineering investigation that included site inspections, component examinations, documentation review, and failure analysis. Engineers inspected damaged and exemplary busway elbow assemblies, reviewed rooftop installation conditions, and evaluated environmental exposure factors associated with the outdoor power distribution system.

The investigation included a review of project documentation, incident reports, testing records, shop drawings, RFIs, manufacturer correspondence, commissioning information, and installation verification testing.

During the inspection process, Envista identified several conditions relevant to the failures. Investigators observed standing water and pooling along portions of the rooftop busway system, evidence of water intrusion within elbow assemblies, corrosion patterns consistent with prolonged moisture exposure, and inconsistent application of the butyl sealant used for weatherproofing.

Engineers also evaluated the condition and tightening of the busway through-tie bolts responsible for gasket compression and sealing integrity. Torque verification testing identified values below the manufacturer’s specified range, creating conditions that could prevent proper gasket sealing and allow water intrusion into the enclosure assemblies.

Further inspection revealed water spotting inside the elbow enclosures and moisture present on insulated busbar components, supporting evidence that water had entered the assemblies prior to the failure events.

Results & Impact

Based on the available evidence and forensic evaluation, Envista concluded that the losses were caused by water intrusion into the busway elbow joints resulting from improperly tightened or inadequately sealed gasket assemblies.

The investigation provided stakeholders with a clear technical understanding of the failure mechanism and informed decisions regarding remediation and redesign of the rooftop electrical distribution system. Following the incidents and subsequent investigation, the rooftop busway concept was abandoned in favor of a redesigned power distribution approach.

Envista’s findings helped the project team assess system-wide risk, support corrective action planning, and move forward with a technically informed path toward restoring reliable electrical infrastructure for the facility.