Built-in Varistor of SPD for Short-circuit Protection A varistor, short for variable resistor, is an electronic component used to protect circuits from excessive voltage or transient voltage spikes. It is also known as a voltage-dependent resistor (VDR) or surge suppressor. Varistors are commonly used in power distribution systems, electronic devices, surge protectors, and other applications where protection against voltage surges is required. They are often connected in parallel with the circui