Puzzling electrical problem (North American outlets and plugs)

Factual Questions
1

Just in case you are concerned, we are not using the outlets with the problem now until a professional electrician comes to work on the room, but I wonder how this weird issue could take place.

In a room that was not used often at the workplace, the outlets (North American standard) in 3 of the walls are not working properly, or poorly. It was not a big problem as the room was not used with electrical equipment until recently.

We tested the light in the switch of a power strip, it looked dim in the 3 bad outlets, so the outlets were not used as devices did not turn on or they didn’t burst.

Now there is one wall where the outlet did work… actually, it looked like it worked, the power light in the power strip turns on brightly, computers plugged to it do work, new digital projectors work, monitors work. But if one connects a set of speakers, with or without the surge protector/power strip, to that “good” outlet, then the speakers are toasted. Same with some fans, and in an old fashion overhead projector, the bulbs burst as soon the power switch was turn on.

One possible clue is that the old over head projector’s instructions reported that the outlet should be grounded, otherwise the bulbs would burst.

This issue was not found by all at the same time, different employees and assistants found the problem intermittently and with the room not used often, it was not until recently that a connection to one likely reason (bad wiring) was made.

Still, it doesn’t explain to us why equipment with ground wire like computers continued to work, but other items with ground wire (like the old fashion overhead projector) did fail. And why other devices with no ground wire also popped and smoldered.

What could be the most likely electrical problem? Yeah, it could be bad wiring, but I have trouble imagining the logic or possible reasons why some equipment did work and others didn’t.

2

Weak or open neutral. With out voltage readings that is just a SWAG.

3

Also, in the computers the ground is “extra safety” but not quite “required”. Sounds like for the projector it was an absolute requirement.

4

all the outlets in the room have a problem.

the room having bad wiring could behave like that, multiple circuits could be involved.

things that didn’t die might have dual voltage inputs and could withstand the higher voltage that might be occurring which might be blowing other things up.

5

That’s my guess from afar as well. If the neutral is “loose” between two phases, one side may be delivering only 40 volts and the other side is getting 200 volts, for example.

Modern computers can auto-sense the line voltage and cope with anything from 100 to 250 volts or so, but your projector and speakers were one-voltage critters that had no ability to handle excess voltage so they failed.

6

NEMA standard 3 prong outlets require 3 conductor wiring from the power supply panel box. This provides ability for using ground fault interrupter circuit breaker type outlets also, a valuable personnel protection. Get a copy of the National Electrical Code book for details of all of the above.

7

I smell a shared neutral problem. You can wire up 2 circuits with the hots coming off opposite legs and sharing a single wire as a neutral. That wire carries the difference in amps between the 2 circuits. Add a bad connection or a few, and who knows what might happen. My guess it the the electronics are set up to detect incoming voltage and use either 120 or 230. Old stuff puts the higher voltage to bulbs and blows them.

8

Thanks for the replies guys, I’m not familiar with electrical wiring so I was not sure what to look for.

Looking around, the “open neutral” got me this:

So a computer or monitor can deal with that, but other lesser electronics will be fried, a followup question: I would think that using that outlet even if computers can deal with it is not a good idea, am I wrong in assuming that even if items can work with that excess voltage that in the long run they are more likely to fail?

9

even if a device didn’t blow up instantly you would be putting it through wear and tear that might shorten its life.

i would stop using all the outlets in the room.

10

Many devices are designed to run on either 120 or 230. They take what they get and do just fine as long as it is consistently one or the other. With flaky connections, the voltage could keep changing or be say 175 instead of either. Unplug stuff for the weekend and wait for the electrician.