Your Surge Protector Can Burn Your House Down!

A business associate recently shared with me some shocking information about surge protectors.  If you are like me, you probably have your computer and monitor plugged into an outlet strip that has a surge protector, right?  They’re supposed to protect  your computer in case there’s a lightning strike or a power surge, right?  Well, maybe.

Over-Voltage Fire
Over-Voltage Fire

It turns out that the MOV’s (Metal-Oxide Varistors) that are used in Surge protectors offer a short to higher voltages but the usual 120 volts pass right on through to your equipment.  Thats good right?  Yes, its good if the transient “surge” is short – like 5 or 6 cycles (1/10 second).  But if for whatever reason your voltage increases to say 208 volts for even just a few seconds,   which can happen if the neutral line of your power feeding your house is compromised, or if there’s a problem with the power feeding your neighborhood, the MOV will quickly burst into flames!  Its made even worse because most surge protector strips are plastic and the manufacturers glue the MOVs into the strip with hot-melt glue!  (fuel source!)

Apparently the Underwriters Laboratory people know about this and are in a quandry about what to do about it.  There are now millions of surge protector plug strips in people’s houses.  And yes, for transient surges they do protect your computer, but for even just a few seconds of overvoltage, they can and will burn down your house!

208 volts applied to a MOV for about 2 seconds
208 volts applied to a MOV for about 2 seconds

This seems like something you’d have heard about on the news, right?  Wrong!  I happen to live in a building that has 3-phase power.  Frequently during storms I’ve seen one of the phases drop while the others stay up, causing…. Overvoltage!  Its a wonder I haven’t had a fire!

I hate to sound like Chicken Little here, but this seems like a serious problem.  I found several websites that talk about how many fires occur near PCs, and they all blame the surge-protected plug-strip.  This is a very real problem!   Check out this recall notice!

I don’t know about you, but I’m going through all my plug strips and snipping out the MOV’s.  I’d rather risk having  no protection from a direct lightning strike (very unlikely) instead of a brown-out, usually accompanied by OVER voltage when the overload is cleared (which has happened a LOT lately) causing my house to burn down!

Images courtesy of Steve Fowler & Associates

UPDATE 6/14/2011: Several readers have asked, here is what the MOV’s look like:

Typical MOV
Typical MOV

Some surge protectors have just one, others have three.  Some have them hot-melt glued into the housing.  Most plug-strip housings don’t come apart easily, you might be better off just getting a plain old non-surge protected plug strip.  If you can get your plugstrip apart you can just clip out the MOV, but be sure you do this with the strip unplugged, and be sure you insulate the old leads  with electrical tape so they don’t short out.  If you’re not comfortable with electrical wiring, don’t try this!  Just get a plain plug-strip.  Here’s more pics of  MOV-caused plug-strip fires: (courtesy University of New Mexico)



7 thoughts on “Your Surge Protector Can Burn Your House Down!”

  1. This is an old article, but it still ranked fairly high in my Google search. So: It might have been good to mention that the latest UL 1449 surge suppressor rating addresses the risk of fire by requiring resistance to sustained over-voltage, or a thermal cutoff meant to prevent the MOVs from igniting. So, if one still desires some surge protection, upgrading to the latest 1449 suppressors is an option. No guarantees, but lower risk. And to be extra cautious, switch off/uplug any protector while away.

  2. Years ago at a company in Johnson City, we were getting a diesel-powered generator installed to provide backup for all IT systems. I was out with one of the electricians who was hooking it up. He did something and we heard what sounded like an explosion, a big boom in the server room. I ran into the room to see a number of UPSes melted and smoking. Unbelievably, we didn’t lose a single server or network device!

    The company had several ex-TI electrical engineers involved, and a couple of them said that they thought the electrician had touched neutral to ground or something similar… don’t recall exactly, but they were in agreement what had happened.

  3. Hey Cliff!
    Depends on the UPS. It would only make sense to put the MOVs across the input to the UPS since the output is supposedly going to be clean.
    Some UPSs kick in when they detect a surge, which would be good.
    I think if there are MOVs across the input, overvoltage could cause a fire. I guess they need protectors to protect the protectors!

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