What happens if the wrong selection has been made at the wrong time?

Not all IR locos have protection against incorrect line supplies, and the loco can be severely damaged in such cases.

In some cases, this will blow a fusible link located near pantograph, and the driver will have to raise the appropriate ALT pantograph to continue. No further damage is possible because the only equipment that is live when pantograph is being raised is the voltmeter. All others like the compressor, exhauster, and motor-generator have to be switched on manually after the pantograph is raised and the voltmeter shows the correct reading.

Source - IFRCA.org