Triangle Waveform

[451F]

What are possible sources for a triangle waveform between pipes in a residential neighborhood? The frequency was ~60 HZ. (59.63)

Arcing has perforated a copper pipe that was touching a steel drain pipe. There is about 1 volt difference between the pipes now as measured on the Low Z setting on a Fluke 117 DMM. The copper pipe tested as bonded to the building electrical system.

The steel drain is connected to the sinks with plastic traps so there is not the usual short between drains and copper.

The voltage difference varied over time with no relationship to equipment cycling in the building.

Thanks in advance for your time and comments.​

 

[G._S._Ohm]

What are possible sources for a triangle waveform between pipes in a residential neighborhood?​

1 volt along a conductive pipe means pretty high current in that pipe.

A symmetrical triangle wave = odd harmonics = 'pollution' from the power grid. The odd harmonics in a square wave fall off more slowly than for a triangle wave.
A sawtooth nonsymmetrical wave = even harmonics.

I had a raggedly looking triangle wave show up for the current drawn from a rack full of equipment containing mostly switch mode power supplies.​

 

[451F]

So, desktop computers could generate the waveforms on the drains?

 

[sameguy]

Not sure what wave form is produced by a computer power supply, it is known that they do produce harmonics.
What about CFL lamps? The more we go "green" the more our power my become dirty; please check what a CFL is putting out with your scope.

 

[451F]

No CFLs here! Does anyone have one they could test for me? Kidding.

While it is an interesting question, it really does not matter as there were no sources of electrical disturbance in the building. Turning on and off equipment did not affect the readings at all.

All I have to do is describe what is there, and if the installer of the copper pipe is responsible for the hole.

Thanks for all of your input.

Cheers!

 

[sameguy]

Dimmers can produce saw waves.

 

[LarryFine]

It sounds like there's a potential difference between the electrical neutral/ground and the earth. Likely electrical cause is a poor service neutral pathway.

 

[brian john]

Have you measured current at various locations?

Measure for zero sequence current at the main service.

Measure for ground current on the main neutral ground bond.

Measure for current at the electrodes.

Isolate the branch circuit neutrals and megger them to verify no shorts to ground.

Is there a common transformer feeding this house and others? With metallic water piping between the units?

 

[dbuckley]

Sure its a triangle? Do you trust whatever you are doing to display this waveform?

There are no interfering things I can think of that produce triangle waves. Most often for voltage is sine waves with notches caused by significant step changes in current flow, usually from something electronic chopping the wave and producing harmonics, stuff like computers, copiers, electronic ballasts etc.

 

[mivey]

Low-amplitude approximate sinusoidals can look triangular in shape (like neutral-ground waveforms). Increase the volts/division on your scope. Can you post a picture of the waveform?

 

[451F]

Job is finished. Report is sent. Site is 9 hours from Shop round trip.

Thanks for the comments and questions.

Bottom Line: The hole is not the fault of the pipe installer.

Cheers. (Sorry there is no time to discuss or test further.)