What electrical event killed my wife's laptop and printer?

January 24, 2008 10:04 AM

What electrical event killed my wife's laptop and printer? We connected the printer to the laptop and...fireworks!

Here's what happened: she plugged her Dell into an outlet (no surge protection) on one side of the room and plugged the usb connection from our printer into her usb port (the printer was on a surge protector). Power connection at the computer sparked, popped, and smoked, the breaker was tripped, and both laptop and printer will not power up.

We're in an older home that we just moved into and i have some suspicions about the wiring but have no electrical knowledge. Can anyone help?

posted by ransom to computers & internet (7 comments total)

You can buy a cheap little gadget at the hardware store that will tell you if an outlet is grounded, or not, etc. Definitely worth investing the few bucks to check the rest of your outlets.
posted by mikepop at 10:18 AM on January 24

Without seeing the plugs, if you are in a country with polarized outlets (eg: North America) and these items have polarized plugs: Hot/neutral wired backwards in one socket.

If one (or more) of the plugs is grounded: Neutral/ground swapped in one outlet, or (unlikely, since you didn't say YOU received a shock) hot/ground somehow swapped in an outlet (how you'd do this and still ground the box, I don't know).

If you know how to safely use one, use a voltmeter to check your outlet wiring. North American standard 3 prong outlets with the ground at the bottom have neutral on the left, hot on the right, and, well, ground on the bottom. You should measure full voltage (120 V here) between hot and ground. With some load on the outlet (plug, say, a 300 watt halogen lamp in the other half of the outlet) you should measure much less voltage between neutral and ground, and little to no voltage if there is no load on the entire circuit. You should always measure the full voltage between neutral and hot. If you are unsure of your results, repeat, using the box itself as ground (assuming it is metal). If you get differing results, you have a problem.

If any outlet fails these tests, well, there's your answer. Some products (illegally in N.A.) use the neutral as a chassis ground. Imagine what happens when you introduce one neutral to another that is actually hot...

Ever washed your hands and used the range full tilt at the same time? That's neutral as a (bad) chassis ground in action.
posted by shepd at 10:25 AM on January 24 [2 favorites]

Seconding most definitely miswired outlets as identified by shepd. The sparks and circuit breaker tripping are classic signs.

You want to get an outlet tester and check all the outlets in your house. Then get an electrician to rewire them for you.
posted by jdfan at 12:08 PM on January 24 [1 favorite]

Wow, that sucks.

Had you used this same outlet configuration before? The laptop here, the printer there, the same surge protector?

I'd still, for my own peace of mind, get one of those outlet testers that others have recommended and test the outlets. And the surge protector. Frankly, I would mistrust the surge protector before my house's wiring, but that's me.
posted by gjc at 1:23 PM on January 24

Yeah, nthing miswired outlets. It's crummy that it actually blew the computer itself, and not just the power adapter. Sometimes when Bad Things Happen, the AC adapter will end up sacrificing itself, but the computer will survive. Apparently not in this case.

Getting an outlet-tester is a good first step, but if it says the outlet is miswired (as I and others suspect), when you have an electrician in to look at it, ask him to check whether the miswiring is at the outlet, or whether the wires in the wall are swapped, too. There are multiple places where things might have gotten swapped; the outlet is one, but the circuit may be hooked up to the fuse/breaker panel incorrectly, instead. (I.e. with hot/neutral in the wires reversed.) This is a potentially dangerous situation down the road, so if it exists you should have it corrected at the source.
posted by Kadin2048 at 1:41 PM on January 24

Speaking from personal, almost-identical experience: some old houses that have been improperly "re-wired" will have three-prong grounded outlets that don't have the ground wire actually connected to the house's electrical ground*. The circuit supplying one of the two devices has a ground fault, meaning that somewhere that power is supposed to be going to ground it is going back into the system instead. I had a multimeter and could test every outlet. Nothing looked funny at any single outlet, but I was getting 120VAC on the "ground" across two circuits, evidenced by the shock I got while checking the connection between my printer and my computer (only the printer was damaged by all this, in my case).

You need to do two things:

(1) Call an electrician and have him identify and repair the ground fault. Most electrical devices will work surprisingly well with odd power (voltage is, in simple terms, a difference between what's on one side and the other, and as long as the two sides are different enough something like a lamp will work just fine), but you're at risk of a fire if there's a ground fault that shorts or overheats a device that relies on a true grounded outlet for safety.

(2) Don't ever (ever!) connect electronics together like that if they're not plugged into the same circuit**. This goes for TV and stereo equipment, in addition to computers. At the minimum you might get a loud hum from your speakers indicating a ground problem somewhere, but you've already experienced the second worst outcome in this scenario. You don't want to experience the worst one.

* Electrical outlets have three wires now: hot, neutral, and ground. The neutral wire is actually grounded where your house connects to line power, and the ground is supposed to be connected to ground at your distribution panel (AKA breaker box or fuse box). In the old days, the separate ground wire wasn't there, and the circuit depended solely on the neutral leg's ground connection for safety. With a properly grounded 3-wire system, in practice there will almost always be 0V between house ground and neutral, since the physical difference between where they're grounded is often nothing (they might both be connected to the same water line in different places). In a badly upgraded house, someone might have "grounded" the system by connecting everything to a water pipe, without checking to see if that pipe really was itself grounded, and not connected to a non-conductive PVC source. Oops.

** U.S. homes are supplied with what's called split phase power. On any given circuit there's 120V between hot and neutral, but between two adjacent circuits there's 240V difference between the two hot legs. If something went very, very wrong*** you could have 240V (and not just 120V) going across the connection between your two gadgets.

*** This photo illustrates the result of a slightly different wiring failure -- in a different house -- than the one that killed my printer.
posted by fedward at 3:47 PM on January 24

Noting re: fedward warning that because of split phase power you can have 240 volts between separate outlets, this is possible and true (although normally not an issue). But if you are worried about that, you should also know that it is (at least in Canada) legal to wire outlets so they share a neutral, and each half of the duplex is fed from one of the two phases of the circuit, so the entire outlet would offer 240 volts if an appliance plugged into both outlets on the duplex at the same time (not legal if you don't have a dual-trip breaker/fuse system, but feh). Anyways, if you want to avoid this, and again, know how to use a multimeter, meter between the hots on the duplex outlet. You'll find either 240 Volts on a split outlet with a shared neutral, or 0 Volts on a standard outlet.

If you're wondering where to find such an outlet in your home, start with the ones nearest the sink in the kitchen. If they're not GFCI outlets, and not "T-slot" outlets (that is, the one hole on the outlet looks like a sideways T) then they *should* have been wired like this (in Canada, again). I don't think this was an NEC requirement.

Shared neutral systems like that are actually really neat, and technically save money on your electric bill (since the loss on the copper when using two appliances that are identical is halved). But we're talking microcents of savings per month. :-D
posted by shepd at 9:10 PM on January 24