Series mode seems to mean Zero Surge or maybe one of their rather sketchy-looking competitors. If these devices were so great, I would expect to see a real standard and certification for them. And this seems a bit dubious to me:
> Unlike most surge protectors, Zero Surge products do not rely on the ground circuit for effective surge protection, so you can use them even in ungrounded outlets.
So let’s see… they apparently pass ground straight through (as they should for safety!), and they’re some sort of filter on hot and/or neutral. (I found a sketch online suggesting that they are, in fact, just an inductor on the hot wire.). So suppose a surge happens and, by some miracle, the surge is just a voltage spike on hot relative to everything else, then, into a resistive load, current and hence voltage will be limited. But the load might not he resistive! Into a switched-off MOSFET or similar, the current needed to damage something is really quite low, and the only way this seems like it will work is if there’s enough capacitance somewhere to make the filter work. If there is any filtering on neutral, though, or if ground is contaminated, then I could imagine arcing between the protected circuit and ground.
In any case, this all seems silly. If the service entrance is protected, a hot-only surge seems pretty unlikely. (Your house’s neutral and ground wiring is not that great, and surges can couple inductively from nearby lightning strikes or even result from failures inside the house.)
I’ll stick with conventional surge protectors.
(I do own a Zero Surge that I bought to test as an EMI filter. I had such bad EMI on one circuit that it made a computer buzz very audibly — this was caused by cheap LEDs dimmed by a mediocre TRIAC. The result: the Zero Surge buzzed even louder than the power supply!)
