Surges and Spikes

Air conditioners, Refrigerators, and Elevators are high-powered equipment. This equipment has motors and compressors and they require a lot of energy to switch on and off. 

The sudden switching causes surges and spikes on the power line & if not properly handled then these can damage the device or machine. 

Power-line surges can easily reach 6,000 volts. A power surge or a spike is an increase in voltage significantly above the standard voltage of 230 volts.

A Surge lasts 3ns or more. 

A Spike lasts 1-2 ns.

Surge

Spike

In order to protect our devices from the above cases, we need to build a Surge Protector. We make it by combining 2 electronics components named Varistor & Fuse 

Varistor

A varistor is a special type of resistor that is used to protect circuits against high transient voltages. A varistor is also known as VDR ( Voltage Dependent Resistor ) 

                   

                                    

Under normal conditions the resistance of the varistor is very high. When the connected voltage gets higher than the specification of the varistor known as the Clamping voltage, the resistance immediately gets extremely low thus current starts to flow through it 

Fuse

When High current flow through a fuse it melts and makes the circuit open 

Combining the above 2 components we make a surge protector. Fuse is in series and VDR in parallel. 

surge protector

The varistor is simply connected between line and neutral but after the fuse. If the voltage across varistor exceeds it's threshold then it acts as a short circuit thereby making high current flow through the fuse which in turn gets melted and open resulting disconnection of the Appliance from the mains supply 

For 230 V mains a varistor of 275 V clamping voltage is a good choice.