Why whole house surge protectors are not enough
TL;DR:
One measure of a surge protector is the clamping voltage. That is, at what voltage does the surge protector actually start to work. Whole house surge protectors are limited to no less than ~ 600 Volts (instantaneous) between a leg and neutral or ground. That’s up to 1,200V if symmetrical.
The best surge protecting strips and conditioners clamp below 200 Volts.
Please keep this in mind when deciding whether or not to use surge protectors at your PC, stereo, TV, etc. in addition to a whole house unit.
I wrote more about this here:
https://inatinear.blogspot.com/2021/09/time-for-new-surge-suppression.html
No manufacturer of whole house surge protection claims that their devices alone are enough for sensitive electronics when you check the fine print.
From an important textbook:
"Art of Electronics 3rd Edition", Horowitz and Hill, page 38. |
Erik, thanks for this thread! This brand was recommended as the very best by an electrician recommended from a reputable audio dealer: Any comments on this brand? They are pricey at $1400 but have lifetime warranty and made in US. They have a few pdfs showing complex protection for the home. By putting it in the panel and behind a pair of 30A breakers, I assume that the idea is that the MOVs will be just slightly removed from the signal path and so interfere with that wave less during normal operation and have less detriment to sound quality. How are we to understand Maximum Limited Voltage in this context? I'm looking at model TK-TTLP-1S240-FL with MLV ratings as follows: 2kV,67A - 36V, 6kV; 3kA - 590V; and 20kV, 10kA - 970V. I think this means for an impulse of less than 2kV and 67A, the clamping voltage will be about 120+36=156V. I agree that a panel installed protector does nothing for induced EMF from a nearby strike, but I had a strike 20 years ago that took out the speaker and amp channel that were closest to it but not the other channel. I assume that was due to induced EMF in the speaker wire or even voice coils. Point is, if lightning strikes really close, all kinds of problems may occur including on the ground leg. Does anyone have an opinion on these? https://ep2000.com/products/home-protection-products/premium-surge-protection-filter/?v=e75edac1b83f |
@nagel I don't know of any SPDs in panel that activate below 600V due to reliability/safety issues. That is, they can't use MOV's with lower voltages because they could activate too often. For this reason almost all SPD makers for panels have about the same clamping voltage. I think the Maximum Limited voltage is AFTER the MOV has activated. It goes up with more circuit resistance to ground. In other words, you could see a 600 V or higher at the AC line before the MOV kicks in. This is why downstream strips which can safely clamp ~ 200V can be so helpful. Not to mention, any series filtering will slow the pulse down so the protector can activate. |
So, MOVs are not perfect, or instant. They live in two states, denial and confusion. Hah! I mean, on and off. When off, they conduct no current at all. However when they DO turn on they are not perfect, which is what is meant by Maximum Limited Voltage. Essentially this is Ohms law:
V = A * R In other words, the voltage that remains at the MOV is proportional to the current it's shunting AND the MOV's resistance. In a perfect world, R would be 0 and therefore V would be zero. A perfect switch, and no voltage across it, but since MOVs are not perfect, even when they've fully activated and are conducting they will have some voltage across them. |
