An adjustable speed drive, ASD, circuit comprising: an input connectable to an AC source; a solid-state switch rectifier bridge connected to the input and configured to convert an AC power input to a DC power, the solid-state switch rectifier bridge comprising a plurality of switching elements; a DC link coupled to the solid-state rectifier bridge to receive the DC power therefrom; a DC link capacitor bank comprising at least first and second capacitors (72, 74) connected to the DC link and configured to smooth a DC link voltage, the first and second capacitors (72, 74) being coupled in series with each other and each capacitor (72, 74) of the DC link capacitor bank having a respective capacitor voltage thereacross; a pre-charge circuit coupled between the input and the DC link capacitor bank, the pre-charge circuit comprising a plurality of pre-charge relays (RY1, RY2, RY3) each operable in an on state that allows the AC power input to electrically connect to and power on the switching elements of the solid-state switch rectifier bridge during a normal operating state and an off state that allows the AC power input to electrically connect to and pre-charge the DC link capacitor bank through a pre-charge resistor of the pre-charge circuit during a pre-charge operating state; and a protection circuit comprising a protection relay coupled between the plurality of pre-charge relays (RY1, RY2, RY3) and the DC link capacitor bank, the protection relay being configured to operate in an on state that prevents the pre-charge circuit from connecting to the DC link capacitor bank when a short circuit occurs on one of the first and second capacitors and operable in an off state that allows the pre-charge circuit to electrically connect to the DC link capacitor bank. an input connectable to an AC source; a solid-state switch rectifier bridge connected to the input and configured to convert an AC power input to a DC power, the solid-state switch rectifier bridge comprising a plurality of switching elements; a DC link coupled to the solid-state rectifier bridge to receive the DC power therefrom; a DC link capacitor bank comprising at least first and second capacitors (72, 74) connected to the DC link and configured to smooth a DC link voltage, the first and second capacitors (72, 74) being coupled in series with each other and each capacitor (72, 74) of the DC link capacitor bank having a respective capacitor voltage thereacross; a pre-charge circuit coupled between the input and the DC link capacitor bank, the pre-charge circuit comprising a plurality of pre-charge relays (RY1, RY2, RY3) each operable in an on state that allows the AC power input to electrically connect to and power on the switching elements of the solid-state switch rectifier bridge during a normal operating state and an off state that allows the AC power input to electrically connect to and pre-charge the DC link capacitor bank through a pre-charge resistor of the pre-charge circuit during a pre-charge operating state; and a protection circuit comprising a protection relay coupled between the plurality of pre-charge relays (RY1, RY2, RY3) and the DC link capacitor bank, the protection relay being configured to operate in an on state that prevents the pre-charge circuit from connecting to the DC link capacitor bank when a short circuit occurs on one of the first and second capacitors and operable in an off state that allows the pre-charge circuit to electrically connect to the DC link capacitor bank.