net current frequencies

[grogerq]

In a net current scenario is it possible to observe AC magnetic fields at frequencies other than 60Hz? We are seeing components between roughly 10 - 15Hz in our site survey in a large old building; but we're not sure if we can attribute those fields to a net current, miswiring issue.

Does anyone have a similar experience that might relate such low frequencies to a net current issue as the cause?

 

[GoldDigger]

In a net current scenario is it possible to observe AC magnetic fields at frequencies other than 60Hz? We are seeing components between roughly 10 - 15Hz in our site survey in a large old building; but we're not sure if we can attribute those fields to a net current, miswiring issue.

Does anyone have a similar experience that might relate such low frequencies to a net current issue as the cause?

I am not aware of any types of loads or wiring problems that would result in a subharmonic (lower frequency) current from a 60 Hz or 50 Hz service.
There are some special applications, like electric rail that use lower frequencies and with an earth return path may cause stray voltages and measurable earth currents over a wide area around the right of way.
Look for voltage gradients between isolated (no connection to GES) ground electrodes in different parts of the property.

Just how large are these magnetic fields, and are there comparable or higher magnitude DC fields?
I could imagine some low frequency fields being measured as a result of building vibration in the presence of high permanent magnetic fields in the structure or contents of the building.

 

[Jraef]

Any chance there is an gantry train rail system in this building somewhere? Old cycloconverter drives systems were sometimes used for electric traction drives on old parts delivery systems in warehouses. I've run across that twice on old buildings from the teens and 20's or so. In one case the traction gantry trains hadn't been used in decades, but nobody had turned off the equipment. The ancient cycloconverter was sitting there humming away, people thought it was just a transformer or something.