Too much surge protection?

[Harry Bloomfield]

If they can survive long enough to allow the fuse / MCB to cut the power then the chances are the item they are protecting will not be harmed.

..but the chances are the MOV will be taken out, not able to provide any further protection and the operator will not be aware of that fact. In Gasguru's example, the sequence might well have been -

1 MOV provides protection once against the first surge and self destructs.
2 A second surge then takes out the PCB, because it no longer has any surge protection.

 

[aptsys]

..but the chances are the MOV will be taken out, not able to provide any further protection and the operator will not be aware of that fact. In Gasguru's example, the sequence might well have been -

1 MOV provides protection once against the first surge and self destructs.
2 A second surge then takes out the PCB, because it no longer has any surge protection.

That's not strictly true - It depends on the energy in the surge. MOVs will happily repeatedly dissipate surges within their repetitive surge rating. The MOVs in most pieces of equipment are happily dealing with transients all day long, it's only when something more serious happens where there is some destruction.

Depending on the energy involved, it won't necessarily blow any protective device.

 

[SUNRAY]

I'm going to stick a spanner in the works and say I've had several situations where there are multiple MOV's on the same circuit due to multiple devices containing them and one MOV destructs with a very loud bang/puff of smoke/smell, no sign of any other damage, nothing else blown up, no fuses/MCB's/RCD's tripped, no lights flicker, no interuption to the correct operation of the kit.
One does start wondering if MOV's are all they're cracked up to be.

 

[Harry Bloomfield]

That's not strictly true - It depends on the energy in the surge. MOVs will happily repeatedly dissipate surges within their repetitive surge rating. The MOVs in most pieces of equipment are happily dealing with transients all day long, it's only when something more serious happens where there is some destruction.

Reminds me of a surge protection gadget I came across, which had a randomly flashing light on it, supposedly indicating the surges and that it was doing its job. It was entirely fiction, the light just connected across the L+N to impress the natives. Minor, short duration surges will have little effect on most equipment, it the larger surges and over voltages which can do the damage and which MOV's cannot cope with.