In my "supposedly" surge protected power stripe there is a varistor for surge protection configured to simply short-circuit the entrance wires in case of surge.
Checking the model it's a MOV-7D471K that on Mouser is reported having the following specs:
Voltage Rating DC: 517 VDC
Clamping Voltage: 775 V
Diameter: 7 mm
Peak Surge Current: 1.2 kA
Surge Energy Rating: 30 J
Capacitance: 105 pF
This has confused me since these values seems to me too high considering that is supposed to protect a 220-240vac max line (European domestic distribution range), and searching on web seems that is often used this MOV for domestic surge protection.
I have seen also that MOV-10D221K seems having values more near to 220-240vac:
Voltage Rating DC: 242 VDC
Clamping Voltage: 360 V
Diameter: 10 mm
Peak Surge Current: 2.5 kA
Surge Energy Rating: 32 J
Capacitance: 450 pF
Why is used MOV-7D471K rather than MOV-10D221K (or some other, suggestion are welcome)? Is my power stripe bad configured or I'm missing something?
Best Answer
You must be reading the specs wrong. A 10D221K would blow up when connected to 240VAC mains as mains have about 340V peak voltage, and so something else must be used.
10D221K can handle max 140 V RMS or 180V DC, and starts conducting 1mA at voltages between 198 and 242 V. It will clamp to 360 V, when 25 A is flowing. It just is not compatible with 240 VAC mains.
7D471K can candle max 300V RMS or 385 VDC, starts conducting 1 mA between 423 and 517 V, can clamp to 775 V when 10 A is flowing. No problem at 240 VAC mains.