Industrial Surge Protector Teardown

Surge protectors are a common item in the modern household, but the Meanwell unit that [Big Clive] tears apart was clearly intended for commercial use. In fact, he mentions it was made for outdoor signage. Removing the rear panel didn’t help much — the entire unit was potted in resin — but that didn’t stop [Clive]. Removing the resin revealed only a few components surrounded by a sand-like substance.

There’s no circuit board inside. Components are just wired together before potting. The significant player inside is a metal oxide varistor with a thermal fuse. [Clive] draws out a schematic, which is deceptively simple. The two LEDs are an older style of green LED, and he explains why the choice of LED is important in this application. In typical operation, the LEDs light. If a fuse blows, at least one of the LEDs will extinguish.

Not all useful circuits have to be complicated. This is an excellent example of how a simple but well-constructed design can succeed commercially.

Not all surge protectors are built this well. If you need a refresher on how varistors work, we can help with that.

12 thoughts on “Industrial Surge Protector Teardown

    1. Agreed they could have picked a better name. It’s no Lambda or HP, but Meanwell is definitely a notch or two above your typical Amazon-grade power components. Do a side-by-side teardown and it’s obvious.

    1. “…I had a Siemens FirstSurge Pro (FS140) whole house surge protector installed.”

      Anything that uses “surge protector” and “whole house” (whole anything in-fact) in the same sentence is designed badly – it is a “single-point-of-failure” design (SPF or SPoF). Common-sense power distribution does exactly what it says, “DISTRIBUTE” the power to where it is still needed and remove only the branches that fail. Each branch has a fuse with an indicator. In a modern system you can service a failed branch safely without affecting the good branches. Of-course, when it comes to electrical distribution systems, YMMV. It’s always good to check your system first to understand what you’re dealing with – especially with old installations.

  1. I’m still using Zero Surge units and have been very very successful with them.
    Unlike MOV based units they do not use sacrificial comments.
    MOV’s degraded and there is no way to test them in circuit.
    The test of an MOV is destructive to the device.

    The problem in a house is two fold.
    First you have small 1200V surges occuring all day long from any inductive load in house.
    The second is that the ground the surge protector is not actually connected to earth ground but earth ground plus x amount of wire that has inductance and capacitence.

  2. Described is secondary protector. It has internal fusing to disconnect, which if you don’t notice that the LED is out, leaves your device without protection for the next hit. For tower/cell sites, and by extension if you want for your own house, use devices rated under UL 1449, the Standard for Surge Protective Devices (SPDs), edition 5 issued January 8, 2021. All MOV’s fail short and hot. In a high end unit, it doesn’t have internal fusing, but is robust enough to open the upstream fuse (like 100A or 200A mains fuse). Then you do know you were hit and that the MOV did it’s job. Temporary power recovery is possible by disconnecting the MOV… yeah… requires an electrician. They rarely fail!

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