IESO Electrical System Voltage Reduction Tests

January 21, 2022 update: The System Voltage Reduction Test was cancelled for February 1st due to covid concerns.

Windsor ON: The Independent Electricity System Operator (IESO) will be conducting two voltage reduction tests on Tuesday, February 1, 2022 as follows:

  • 3% voltage reduction test from 9:00 am until 10:00 am.
  • 5% voltage reduction test from 1:00 pm until 2:00 pm.

The IESO regularly tests its emergency procedures. Testing includes a system-wide voltage reduction test every 18 months. The purpose of the test is to assess the effectiveness of voltage reduction, to ensure staff familiarity and to identify procedural deficiencies.

The service voltage supplied to our customers will remain within the normal operating voltage range during the tests. It is expected that our customers will not be impacted by the voltage tests.

The IESO is responsible for controlling the operation of the high voltage transmission system in the province, maintaining the integrity of the system and responding to power disturbances. System voltage reduction is an operational procedure used by the IESO to manage the reliability of the power system when demand for electricity exceeds supply.

ENWIN is directly connected to and receives all power from the IESO controlled electrical system in Ontario, and - along with all other electricity distribution companies in Ontario - is a participant in the IESO voltage reduction testing.

For additional information about the reliability of the Ontario Power System and voltage reduction, please visit the IESO website at