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I live in a (rented, 1980 built) row townhouse in the USA with slightly suspect electricity:

  • A few of the outlets and light switches in the house (in various rooms) don't work at all. (Even allowing for some switched outlets.)
  • My five year old desktop computer on the ground floor developed a bad power supply a few months after moving in. (After a cross-country trip in a moving van, and it is an old computer.)
  • Plugging anything into one outlet on the ground floor often shorts out the rest of the stuff in the room. (We avoid using this outlet!)
  • A 5-6 year old laptop's power adapter doesn't work on the ground floor, but does work upstairs. (A newer laptop works both upstairs and downstairs, so it's possibly a bad power supply on the old laptop.)

Given that the computers in question are 5-6 years old, and we jostled them across the country moving, it's entirely possible that their time had/has come and they need to be replaced. However, before I buy and plug in a new desktop (or keep using my other newish computer) with this potentially suspect power, am I right to be concerned about it? Could the damage have been caused by the times we've shorted out the downstairs room? Or maybe slowly over time by bad power?

If I had a multimeter or some other test device, could I test my outlets and/or electricity? Do I need to call an electrician? Should I just assume that my computer died of old age and replace it without worrying that the new one will meet a similar fate?

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Not related to fixing the root of your problem, but a couple comments: a UPS with AVR (auto voltage regulation) will help smooth the power. Not all computer/laptop power supplies are created equal. The cheap supplies are cheap for a reason, and don't handle poor line conditions well. The more expensive supplies have better circuitry that can handle varying input conditions a bit better and produce more reliable output. –  gregmac Jan 9 '12 at 16:14
    
Thanks for all the help. I'm going to start with an outlet tester and proceed from there. If it gets crazy I'll have my landlord call an electrician. @gregmac, thanks for the info about power supplies too -- the newer laptop is nicer than the older one and likely has a better power supply. Maybe that's why the new one works both places and the old one works only upstairs. After testing my outlets, maybe I'll be moving my home office upstairs! –  Mike Kale Jan 9 '12 at 21:48
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2 Answers

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Yikes, it sure sounds like you have several issues with your electical wiring there. I won't speak too much to your power supply issue, but really think you should invest in a UPS to mitigate any power related damages to your equipment.

Now lets correct a few mistakes in the previous answer.

The 120VAC legs of your electrical service are supplied by two separate hot feeds from the power company. The neutral is not there to split the 220VAC, but rather to supply a return path to the service panel and ultimately earth ground.

The neutral should be at the same potential as ground. An open neutral is checked by measuring neutral to ground, if line voltage appears, then in fact the neutral path to ground is open. Unless you have a situation where both 120VAC legs are in contact with one hot connection, you cannot produce more than 120VAC on any open neutral. If you were to see 140VAC on any hot to ground or neutral, or neutral to ground, then you have some serious problems and time to call the landlord before you fry all your lights, appliances, and electronics. This situation is very rare, and I don't think it is your problem. Your problem sounds more like a bad connection, either hot or neutral in some device that feeds your downstairs outlets.

This can be a frustrating and time consuming job to track down this type of problem. It may involve pulling several devices out of the boxes and testing voltages with the power on, and also testing conductivity with the POWER OFF. Unless you have the experience and you feel very comfortable working on hot wiring, I'd suggest you have the landlord call in an electrician ASAP.

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The symptoms of an open neutral vary, depending on where the fault lies. If it is close to the outlet and you have a low-impedance device connected in parallel, then indeed you can see line voltage (and the device won't work); if it's close to the utility panel, then you would see the effects described in the other answer, although his voltage calculations are way off because they do not take phase into account. –  Simon Richter Jan 9 '12 at 13:17
    
Note, there are many types of UPSes, not all of which will solve problem. The cheapest "standby" type simply switch to battery after mains is lost, but otherwise pass it through. You can still have problems on this. The more expensive "online" UPSes always run from battery giving a very clean and steady output, and simultaneously charge the battery while mains is available. However, most UPSes have decent surge protectors built-in, which you should have on really all sensitive electronics (not just computers). –  gregmac Jan 9 '12 at 16:19
    
Some UPS's will actually log line voltage fluctuations, so they can also help you determine if you have power issues. –  Tester101 Jan 9 '12 at 18:55
    
Yep, I should have been more specific. A UPS with full power conditioning. AC to DC and inverted back to regulated AC , then a little battery back up to shut down programs without losing data in a power failure. Gregmac and Tester, you are both spot on. –  shirlock homes Jan 9 '12 at 22:49
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The worst electricity fault that a house or apartment can have is an open neutral. The neutral is the wire that splits the 220V coming into the house into two different 110V feeds. If the neutral is open, there is nothing keeping them both at 110V. For example you could turn a light on, and the side with the light could drop to 80V, and the other would go up to 140V.

Some of the outlets in your apartment are tied to one side, the rest are tied to the other.

You can check for an open neutral by turning lights on and off throughout the apartment. If turning on a light in one room makes the light brighter in another, you have an open neutral. You shouldn't use your computer, in fact you should get it fixed immediately, it's quite dangerous.

Other possible faults include swapped wires on the outlet, open ground, open hot. These can all be checked with a $5 outlet tester that you buy at Home Depot.

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The outlet tester you want looks like this: diy.stackexchange.com/a/1032/80 –  Jay Bazuzi Jan 9 '12 at 7:41
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From Wikipedia: "A transformer supplying a 3-wire distribution system has a single-phase input (primary) winding. The output (secondary) winding is center-tapped and the center tap connected to a grounded neutral. This 3-wire system is common in countries with a standard phase-neutral voltage of 120 V. In this case, the transformer voltage is 120 V on either side of the center tap, giving 240 V between the two live conductors, The two outputs are properly called "legs", not "phases"." –  Steven Jan 9 '12 at 17:36
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@JoeAugenbraun What I'm saying is, if you are seeing a voltage swing like this the problem is likely between the distribution transformer and the load center. It's more than likely a problem that can only be fixed by calling the power company. –  Tester101 Jan 9 '12 at 18:11
    
Thank you Steven, I hate it when people call legs phases. that tells me immediately they don't know what they are talking about. –  shirlock homes Jan 9 '12 at 22:51
    
@shirlock: nah, he was just pulling your phase. –  Jay Bazuzi Jan 10 '12 at 3:58
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