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IESO to Conduct Routine Voltage Reduction Test

July 17, 2019

The Independent Electricity System Operator (IESO) will conduct a routine voltage reduction test on Thursday, July 18, 2019, as part of mandatory testing of its emergency operating measures. The test, which is not expected to impact the public, is an important tool for ensuring the reliability of Ontario's electricity grid.

Voltage reductions lower demand quickly and minimize the likelihood of service interruptions, helping the IESO maintain the reliability of Ontario’s power system during a variety of unplanned occurrences.

A three-percent reduction is expected to occur from 9 a.m. to 10 a.m. EST. A five-percent reduction is planned for 1 p.m. to 2 p.m. EST. These tests are normally conducted every 18 months.

Voltage reduction tests have three key purposes:

  1. To determine how much power can be reduced through the two levels of reduction.
  2. To identify equipment problems so they can be addressed.
  3. To help keep IESO and market participant staff familiar with procedures to execute voltage reductions and identify any deficiencies in the procedures that may need correction.

Consumers with questions about the test should contact their local distribution company. A list of local distribution companies is available.

More information about voltage reductions is available on the IESO website or by contacting IESO customer relations at 1-888-448-7777.

About the IESO
The IESO operates Ontario’s power grid 24 hours a day, 365 days a year, ensuring Ontarians receive a reliable and cost-effective source of power when and where they need it. It works with sector partners and engages with communities across Ontario to plan and prepare for the province’s electricity needs now and into the future. Visit for more information.


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