This question follows from this other question where the OP mentions that:
I know MOVs inside surge protectors degrade over time
Based on this it seems that surge protectors eventually deteriorate past a point where they do not provide (expected) protection against power surges.
The questions I wanted to ask about this:
- Is it correct that surge protectors degrade, and if it is, what causes this?
- Is there a rule of thumb for determining how long a surge protector can last before needing to be replaced?
- Are there ways to determine if a surge protector is old (or otherwise faulty, for that matter)?
Best Answer
It truly depends whether your surge protector contains MOVs or not.
The wear mechanism for a MOV is that the clamping voltage DECREASES slightly every time the MOV is required to clamp a transient. Eventually, the clamping voltage decreases to the point where the MOV starts to conduct on the peaks of every AC cycle. The MOV will then burn up.
FWIW - the early cube plug-in surge protectors manufactured by RCA had a clear plastic window on the side that showed the red MOV inside. A label on one side of the cube said something along the lines of; "If it's black, take it back."
More modern surge protector power bars have thermal cutouts mounted between the MOVs. If a MOV flames, the thermal cutout interrupts the incoming power.