Component Id

[anvoice]

Hello, a friend asked me for help with replacing a bad component on a device. The photo is attached. To me it looks like an inrush-limiting thermistor, with what appears to be a 150V rating. If this is for a power supply (as hinted at by the isolation slot in the PCB), this is slightly strange because they live in a region with 220V. That could explain why it broke in the first place, assuming I am correct.

Is this indeed a thermistor? I can't read the current rating if it has one, so I was going to ask for a better picture, but should I tell them to replace it with one rated for over 220V?
Thanks in advance.

[Benta]

Varistor.

[anvoice]

Right, thank you, the proper tern is varistor, or MOV.

I got a little more information: seems like they destroyed the varistor by plugging their device, whatever it is, into 220V when it's rated for less. Apparently they now have a 220V to 110V converter and the device is working at the moment (I'm guessing they bridged the broken varistor though I don't know for sure). I see something that looks like "A8" and "c700" on the component, but a google of these doesn't lead to a compatible varistor. For selecting a replacement, should I choose one with an equal or higher rating? Is there a way to tell what current the replacement should be rated for, or should I just go on the high side (e.g. 50A) to be safe?

[Gyro]

Right, thank you, the proper tern is varistor, or MOV.

Actually, both. MOV stands for Metal Oxide Varistor.

[anvoice]

Actually, both. MOV stands for Metal Oxide Varistor.

That much I knew.

So is it safe to substitute a higher rated one, or should I use the exact voltage and current rating in the replacement?

[drussell]

So is it safe to substitute a higher rated one, or should I use the exact voltage and current rating in the replacement?

Use the incorrect voltage for a MOV defeats the purpose of having it there in the first place.  it isn't like a capacitor where you can go up in voltage.  Going up in voltage means the MOV isn't going to clamp at the point it is supposed to.  Using too low of a voltage will mean it conducts when it shouldn't and will burn or blow up.

On the other hand, using a "beefier" one rated for more joules of energy dissipation (with the correct voltage for the application) is fine and would normally be desirable if physical constraints allow.  MOV lifetime is somewhat related to the total number of joules dissipated over the lifetime of the device.