wall outlets measuring weird frequencies above 60Hz?

[dentaku]

Why would a wall outlet that measures just fine at around 120V AC not read 60Hz on my multimeter?

There was a brownout and a power surge in our neighbourhood this morning and a nearby office lost power to one end of the building upstairs.
I went to check it out and two "powerbars" were dead (one blew black soot out of a socket) but luckily the two computers and the DSL box connected to them were fine.

I went back home to test my multimeter just in case the frequency measurement was not working but it's reads a solid 60Hz here.

What would make all the outlets in a building measure random frequencies around 80/90/100Hz on my meter?
It would be interesting to see what the waveform looks like but I don't have anything portable I could bring there to test it.

[amyk]

There's probably lots of noise from other equipment. Equipment with SMPS shouldn't be affected since they rectify the input anyway.

[rstofer]

Any other problems in the area.  Maybe an ongoing arcing situation could cause something like that.  Loose wire arcing?

[IanB]

Also, make sure you are using a "Low-Z" mode on the meter.

You could emulate this by connecting a resistive load like an incandescent lamp to the outlet before measuring the frequency.

[dentaku]

Also, make sure you are using a "Low-Z" mode on the meter.

You could emulate this by connecting a resistive load like an incandescent lamp to the outlet before measuring the frequency.

Interesting.

[Curtis]

A lot of high rise buildings some times have similar problems because there are a lot of computers that have "non linear" power supplies which introduce "harmonics" to the electrical grid. Switching power supplies and such can, and often inject harmonic waves, and voltages that can cause all kinds of weird things to happen in the electrical system.

We also see this phenomenon where a electrical system can act like a "antenna" to pick up "rf" energy, and then these frequencies can be heard throgh audio amplifiers connected to the same grid system.