regulator

The voltage regulator stopped working and the resulting overload destroyed the device.

[…]in part because a key county reservoir had to been drained to reduce earthquake risks highlighted by federal regulators.

To start No. S.002 effectively with a heavy train, one opens the main regulator sufficiently to move the train off very slowly. An excess of regulator opening with the by-pass valve open can cause heavy slipping; if the worst happens, the slipping continues a little longer after the regulator is closed than on an English locomotive.