An electrical inverter comprises positive and negative supply lines, first and second thyristors the anodes of which are connected to the positive line and the cathodes of which are connected respectively to the anodes of third and fourth thyristors. An oscillatory commutating circuit including a capacitor and an inductor is provided and which is connected between the anodes of the third and fourth thyristors and also a firing circuit is provided to provide gate signals to the first, fourth, third and second thyristors in that order. In addition, means is provided to over-damp the oscillatory circuit thereby to limit the commutating voltage.