Complex sentence: A sudden fail-open fault can cause multiple secondary failures if it is fast and the circuit contains an inductance; this causes large voltage spikes, which may exceed 500 volts.
Split into simpler sentences: A sudden fail-open fault can cause multiple secondary failures, when the event is fast and the circuit contains an inductance. The suddenly interrupted current flow in combination with the inductance then causes large voltage spikes, which for very fast events may exceed 500 volts.