IESO to Carry Out Routine Voltage Reduction Tests in July 2026
June 25, 2026
Routine voltage reduction tests will take place on Thursday, July 23 as part of mandatory testing of the IESO’s emergency operating measures. The tests are an important verification 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 per cent reduction is expected to occur from 9 to 10 a.m. EST. A five per cent reduction is planned for 1 to 2 p.m. EST.
The most recent tests were held in January 2025. Under North American reliability requirements, these tests are normally conducted every 18 months.
Voltage reduction tests have three key purposes:
- To determine how much power can be reduced through the two levels of reduction
- To identify equipment problems so they can be addressed
- 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 to be corrected.
Voltage reductions have minimal or no noticeable impact on the public as the voltages are still expected to be within established industry standards for electrical equipment used by residential, commercial and industrial consumers.
If system conditions are not favourable on July 23, the alternate test date is scheduled for Thursday, July 30.
More information about voltage reduction tests is available on the IESO's website.