Are series mode surge protectors actually better than MOV based ones?

[TacoMelt]

There seems to be a lot of lore and info around series mode surge protectors. Many say they are great and they come from companies like Surgex and Zerosurge.

It's all very confusing though so hopefully the folks here can clear it up and give advice. I'd appreciate that.

[BenKenobi]

Good ones yes but at 10 times the price. Every time a MOV takes a hit it dies a little, eventually it provides no protection, high end series mode supplies don't 'wear out' in the same way.

A typical MOV based surge protector has a limited lifespan but this depends on the quality of the power in your area, either way it eventually needs replacing - but if you buy one every 5 years for the next 50 years you would have paid for a series mode unit - and would a series mode unit last this long - probably not.

Personally I don't see the point in the expense of series mode unless you're protecting something really really expensive and sensitive.

[TacoMelt]

What if the person using it lives in an apartment that doesn't have a ground? It's an old building and the landlord is not going to fix the electric. So I was curious if series mode was safer than MOV based surge protectors for those who don't have grounds? I worry about fire.

[helius]

It's really hard to know how much a MOV has been used up, and whether it will protect from a future surge event. You can see whether it is absorbing voltage spikes with a power quality meter, but most people don't have those.

In the US, you should have a solid neutral-earth bond at the distribution panel, so the MOV between live and neutral provides (indirect) lightning protection. They do not protect from direct lightning strikes. The voltage rating of the MOVs are also commonly too low: because they are most effective if they are large in size and as close as possible to the power entry, the correct approach is to have a single large MOV at the distribution panel main fuse, which is rated to absorb all power spikes. The small MOVs in power strips should be a higher voltage rating so they only absorb spikes or surges if the previous MOV has failed. Most computer power supplies have MOVs internally, which are the absolute last ditch protection and should have the highest voltage rating of all.

It used to be that MOV based surge protectors had significant safety issues, and many of them were in fact recalled for this. The problem is that when the MOVs were damaged by surges, they could go low impedance and begin to heat up, which eventually ignited the circuit board and wire insulation. The way these surge protectors should have been designed is with thermal fuses directly in contact with the MOVs, to break the circuit in case of overheating. The protection offered by a series suppressor is simpler, doesn't wear out, and isn't subject to overheating.

[james_s]

I don't like MOVs, I've had both a power strip and a UPS burn themselves up on different occasions, and at work we had a UPS catch fire and burn a hole in the carpet a number of years ago. Personally I think surge protectors are overrated and of relatively little value, however I also live in an area where lightning is rare and I've only ever encountered one piece of equipment that was damaged by a nearby lightning strike. That was a dishwasher and it had a MOV built in which was reduced to a black splotch on the board and two ragged wires.