Comment by schiffern

The things people often call "transformers blowing up" are usually not transformers blowing up.

Instead, it's usually just overhead wires that are too close or literally touching, often from influences like wind and ice. The electricity arcs between the wires, creating bright blue-white flashes that can be seen from far away, sometimes with instantaneous heat that makes hunks of metal wire evaporate explosively. It can be violent and loud, and repetitious as different parts of even a single run fail.

Transformers can certainly blow up, but that's less common. They're (generally) filled with oil for cooling purposes, and they're massive things that tend to take time to get hot. A failed transformer can produce arcing and blue-white light, but if things are that hot then the oil is also ready to burn.

And when the oil burns it isn't blue-white -- it burns with about the same yellow-orange color we saw the last time we accidentally flambéed dinner on the kitchen stove, or a Hollywood fireball.

A bright flash without a fire is probably not a transformer.

Here's a video of a transformer actually-exploding (note the prominent fireball): https://www.youtube.com/watch?v=oFkfd31Wpng

And here's a video of what someone describes as a transformer exploding, even though there are no transformers in the video: https://www.youtube.com/watch?v=rHVh0KwG_0k

Definitely use quality surge protectors on expensive equipment connected to generators.

PSA: UPSes and GFCI/GFI extension cords won't work properly when connected to a stand-alone generator with a bonded neutral. I've tried using enterprise UPSes on such generators, but they absolutely won't work. In such scenarios, debond the generator's ground from neutral, apply a very large warning label to it being debonded, and drive a massive ground rod electrode into the ground as close to the generator as possible and ground the neutral there. This does work and is much safer because there's a stable voltage reference source. It's more of a hassle but can be necessary for some off grid and temporary scenarios.

It's not just cheap UPSes, it's cheap surge protectors as well. They exist because the vendor can throw in a MOV costing a few cents and increase the price of the power strip by 50%, not because they're any good. MOVs are sacrificial components which have either degraded to uselessness by the time they're actually needed or, if they're still working, can explode or catch fire from the energy dissipated. Even if they don't, all they're doing is converting an x-kV spike on active into an around-x-kV spike on neutral or ground. If you want to do it properly, use a series tracking filter, not a "surge protector".

> Not only should you get rid of them, but also they are a fire hazard.

Are they not a fire hazard even when new? MOVs do tend to degrade with use (especially after they've gone conductive to snuff one or more surges). But AFAICT we can't really know, without potentially-destructive testing, whether a given MOV is in good shape -- whether installed last week, last year, or 30 years ago.

> Also, do not accidentally plug surge protectors into each other, metal oxide varistors can star fires _without_ meaningful surge conditions when you do so.

What is the mechanism that increases risk for MOV-sourced fires in this arrangement?

I've also noticed that many of the power supplies I've taken apart (for very pedestrian consumer goods) have internal MOVs on their line input. Whatever the mechanism is that increases risk, isn't using one external surge protector already doing that in these instances?

> I prefer to buy products without MOVs entirely due to the risk, with the exception of one, Tripp Lite Isobars; but I prefer to use series mode protectors such as Brickwall or SurgeX.

I prefer to avoid MOVs, too. Broadly-speaking, diodes seem like a better way to do it. (Transtector is another reputable brand that uses diodes.)

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That all said, I've noticed over the years that problems with dead (presumed-to-be-hit-by-a-power-surge) electronics tend to follow particular structures. And the reason for this seems related to grounding more than it is anything else.

So when I find someone (a friend, a client, maybe someone online that I'm trying to help) complaining about repeated damage, I often ask about grounding. Almost always, it turns out that they've got multiple grounding points for the electronics: The electric service has one ground rod, and the telephone/cable feet/satellite/whatever is connected to some other ground.

This might be a dedicated rod, maybe a metal pipe; whatever it is, it is distinct from the main service ground. It happens all the time. (It is worth noting that the NEC prohibits this kind of configuration unless extraordinary effort is put forth. See 800.100(d), for example.)

The way that MOVs -- and avalanche diodes alike -- behave combines with the fact that the earth is an imperfect conductor, such that having multiple ground points promotes dynamic ground loops that can provide quite large potential -through- the electronics that we seek to protect.

The problem appears suddenly, and repetitiously. Everything is fine, and then ZANG: The cable modem gets smoked along with the router it is connected to. So the modem goes back to Spectrum or wherever to get swapped, and the router gets replaced again, until the next time: ZANG.

TV connected to satellite receiver, with coax incorrectly grounded? ZANG. Over and over again.

I'd see it all the time when I was a kid back in the BBS days: The phone line was grounded improperly, and computer was the only thing that connected to both electricity and the telephone line. Some folks would go through several modems over the course of a summer, which was very expensive -- while most people had no problems at all. Next-door neighbors would have completely different failure rates.

Structures with correct grounding tend to do very well at avoiding these issues, and I've fixed these conditions in subsequent years more times than I can count.

(A coworker installed a phone system at a business once, wherein he made extensive use of Ditek surge suppressors -- on the incoming POTS lines, and on the power inputs. It blew up one day. So he called Ditek to try to get at least the cost of the phone system hardware covered. They asked him to draw up a map of how the building was grounded and send that over, so that's exactly what he did. When they saw his map, they very quickly identified a ground loop and denied the claim.)

Another perspective: we should install whole house surge protectors if we can afford them, not only for ourselves, but to help our neighbors - even if in reality the help is minimal and they need their own as well. In the best case scenario, if everybody in a neighborhood has them, each individual house will be more resistant to surges than if they were the only house with one (five houses with surge protectors nearby is a lot better than one) - everybody wins.

You might as well phrase that as "If your close neighbours have gotten vaccines then you benefit little from getting your own."

We live in a society. Everybody chips in. And each surge protector adds to the robustness of the grid.

Eh. Most nice power strips are also surge protectors.

I've lived all over the peninsula, your experience is not normal.

I had far more power outages during my late teenage years in suburban Dallas than I've ever had in the bay. That was due to a bad transformer in the neighborhood which took years to replace, but once it was replaced everything was perfect. The moral of the story being: if your power is bad, it's probably because some piece of mains infrastructure near you is broken.

I had a string of annoying outages in 2023-2024, but it was all due to main service upgrades on my street, can't really complain about that.

Huh, interesting. I've lived in the bay area for 22 years (first 6 of them in various places from SJ up the peninsula, remainder in SF), and I've never experienced damage to anything due to a power surge.

Not saying you're lying, but I do wonder if your experience is typical.

Color me skeptical. I've lived in several different Bay Area cities for decades. There are usually a couple power outages per year but I've never experienced a surge strong enough to cause equipment damage.

Sounds like if you're in an urban area with buried lines, you don't have to worry?