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Grid infrastructureUnited StatesEIR-1034

Ageing transformer explodes at Belmont substation on hottest day of the year, causing blackout

June 2017Published 17 Sept 2026Responsible editor: Chief Editor

SignificantElectrical
Estimated damageEstimated by the register's adjusterHow? Know the real figure?
Figure hidden: shown to subscribersMedium confidence
supply cut for about •• daysShown in the record →Full estimate
From the recordRoot cause hiddenFailed part hidden
Where
Hittinger substation in Belmont, Massachusetts
Operator
Belmont Light
What
transformer exploded
Cause
combination of heat and the age of the equipment
Outcome
outage for quarter to third of residents up to 10 hours; no fire

Companies named in the reporting of this entry (being named is not a finding of fault): Belmont Light

What happened

On 12 June 2017, on what was reported as the hottest day of the year with temperatures above 90 degrees Fahrenheit and electrical demand at a peak with town schools in session, a transformer at the Hittinger substation in Belmont, Massachusetts exploded. The municipal utility, Belmont Light, said the failure was caused by a combination of heat and the age of the equipment. Safety systems acting as a circuit breaker cut the electricity entering the substation, and no fire started.

The outage affected between a quarter and a third of the town's residents, with some neighbourhoods without power for nearly 10 hours. Three rented generator trucks were used to supplement the substation until repairs were completed. The high school ended classes early and pupils at two other schools were kept in their buildings for safety and logistical reasons. A 400 amp transfer switch on one school's backup generator malfunctioned during the event despite passing inspection two weeks earlier, and was scheduled for replacement.

Contributing factors

The utility attributed the failure to the combined effect of high ambient temperature and the age of the transformer, occurring during a period of peak electrical demand. Officials noted that an oil fire, had one started, would have stretched fire resources and caused months of disruption.

Lessons learned

  1. A transformer at a substation failed under peak load on the hottest day. Operators should assess and replace aged units before summer peaks.
  2. Safety systems isolated the fault at once and stopped any fire. Substations need fast acting breakers to limit damage and outage length.
  3. Three mobile generators restored supply until repairs ended. Pre arranged rental contracts can cut outage time after substation faults.

More lessons on maintenance, inspection and ageing assets, electrical protection and isolation, outages, backup supply and restoration, from every incident on the register.

Not yet known

  • Transformer model and exact age
  • Cost of repairs and mobile generation
  • Why the transfer switch failed after recent inspection

This entry is updated when these are reported. Get an alert for the next one like it.

Source

belmontonian.com

Published 2026-09-17. Written from public reporting. Descriptive, not investigative. See the data accuracy disclaimer.

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Substation and transformer fires: the counts, the latest entries and a free alert for the next one. Also: transformer explosions and switchgear and breaker fires.

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