Originally Posted by bobknavs
More personally, I have been using a Furman PST-8 for a couple of years, based on a recommendation from a forum member. I got it as a protection device; I don't get a lot of noise on my power line. (Single family house, neighbors apparently not running lots of power equipment.) It appears to do no harm. I never opened it up, but supposedly it has a lot more internals than your typical sacrificial surge protector. Maybe "b curry" knows better, but I'm skeptical of his skepticism.
Most of the surge protectors from Furman in the $100-$300 range or anyone else for that matter use MOV devices for surge protection. They do offer some level of surge protection but they are not without downsides.
MOV's do not protect equipment from inrush current surges, from overcurrent situations, or brownouts. MOV's degrade with time and use and are disposable devices. Under normal utility voltage conditions, MOV surge protectors work great. But under normal conditions, you don't really need one do you?
MOV based devices cannot withstand sustained over-voltage situations and can result in the MOV device catching fire. I know this from practical experience using an APC branded surge protector. It melted down, caught fire, and burned a hole through the rooms carpet during a lighting strike on nearby power lines. I contacted APC to use the surge protectors APC warranty only to be told by APC that my circumstances were not covered. APC would not even replace the unit let alone pay for the damage. The internet is full of pictures of MOV based power strip fires with a simple search.
The Furman PST-8 is an MOV based device. Yes, I agree it probably appears to do no harm. MOV's work at a designed "clamping voltage". If that design limits current in anyway, you're potentially limiting the output capability of a power amplifier when higher volume demands are placed on the unit. Without test equipment, you can't really tell one way or the other.
Small surges are cumulative for MOV's and will cause there failure over time the same as one large voltage or current strike.
Furman states in the description of the PST-8 that it uses TVZ-MOV's. TVZ-MOV's are fancy MOV's that include a thermal protection fuse. I'm not really sure what Furman's SMP circuit is, some sort of AC voltage filter I guess, but if you look at the circuit board on their site, you can clearly see the MOV's.
From Furman's description of the PST-8:
all feature Furman’s SMP circuit which incorporates Linear Filtering Technology (LiFT) and a high current TVZ-MOV
to insure that …"
Functionally, most any $15-$20 MOV power strip will offer the same level of surge protection as the $150 PST-8 does.