Residual 60 Hz magnetic field

[gar]

151104-1026 EST

The residual 60 Hz magnetic field around my basement, other placres in my home, and the yard is less than 10 microvolts. Where 20 mV = 1 gauss, and thus my residual is less than 0.5 milligauss. Outdoors below my 3 phase primary lines the result is still the meter residual noise level. In the past using a 5' by 20' one turn rectangular loop below the primary lines I could see variations in the output voltage. This had no filtering to remove high frequency noise.

With my probe adjacent to my 1.25" copper water supply line 5 milligauss. Adjacent to one 120 V feeder 100 milligauss, and the other feeder about 30 milligauss.

I used a 1 mfd capacitor in parallel with the magnetic pickup to reduce high frequency noise. The inductance of the magnetic pickup is 116 mH with a Q of 1.2 at 1 kHz, To resonate4 at 60 Hz would require a capacitor of about 65 mfd. With 1 ufd the resonate frequency is about 450 Hz.

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[mbrooke]

Dont forget that EMFs boil into two components:

Electric fields and magnetic fields.

If you have consistent high magnetic field readings in a home most probable cause is a crossed circuit or neutral to ground fault which at 100 milliguas is worth looking into. Wifi and other devices are best switched off when not in use if concerned.

 

[gar]

151104-2050 EST

I started this thread simply to see what sort of responses I might generate. This was an outgrowth of http://forums.mikeholt.com/showthread.php?t=172874 .

The magnetic field sensor is a commericial unit I purchased around 1960 and I don't know the manufacturer. This has electrostatic shielding and thus is primarily sensitive to magnetic fields. Since it is essentially a coil with a large number of turns this means the output voltage at a specific flux density is proportional to frequency. Filtering of the output is desirable.

There are two places in town where I get a substantial hum in the car radio when I am near the power lines. With said magnetic probe I don't measure any signal at these locations greater than the meter noise level (10 microvolts which equals 0.5 milligauss). Thus, I don't know if the hum in the radio is from a 60 Hz magnetic field, or modulated RF signal.

At my daughter's home there is shunt neutral path leading to her air-conditioner. I don't remember the field intensity, and it has not been a priority to find the cause.

I don't have a clamp-on ammeter that will fit my water line, but there is little current flow into the house from the water meter while at this moment there is about 50 ma flow to the street based on the current on the grounding conductor from the main panel to the input side of the water meter. My grounding electrode is my water line.

A magnetic field intensity sensor is not a good way to get an accurate current measurement because it is position sensitive and a function of the current distribution in the conductor. But, it is a way to detect the presence of current.

My magnetic field sensor gives a much lower reading when adjacent to the 1.25" water pipe compared to adjacent to the #6 grounding wire for essentially the same current. This is as expected.

How many readers have used a magnetic flux meter to search for bad neutral paths?

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[GoldDigger]

Not your primary question, but the most likely, IMHO, is arcing leakage across defective insulator(s).
The broadband RF from the arcing is modulated by the power line voltage, dropping out for part of each half cycle. There are probably a lot of harmonics of 120Hz present in the audio. Little or no 60Hz would be there unless the source of the arcing is polarity sensitive.

 

[gar]

151105-0914 EST

GoldDigger:

That is a likely cause.

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[ghostbuster]

"How many readers have used a magnetic flux meter to search for bad neutral paths?"

Yes, we use a mag meter sometimes as a tool to search for bad neutral/grounding conditions.Using a current clamp-on around both the hot and neutral will verify the bad wiring configuration.

Also, many times in large commercial buildings we find the large metal air ducts are conducting current (we use a mag meter as the initial "sniffer")

 

[mike_kilroy]

"How many readers have used a magnetic flux meter to search for bad neutral paths?"

Yes, we use a mag meter sometimes as a tool to search for bad neutral/grounding conditions.Using a current clamp-on around both the hot and neutral will verify the bad wiring configuration.

Also, many times in large commercial buildings we find the large metal air ducts are conducting current (we use a mag meter as the initial "sniffer")

ghostbuster.....emf meters.... moonlight beside electrical work? ever run into the stay puft marshmallow man?

 

[FionaZuppa]

ok, so, ever been on the ghost tour in San Diego at Old Town? at one point he pulls out a special mag meter over a site that had some history, the thing goes crazy, says there are no utilities or odd piping around or underground.

so, it is possible that its just a matter of mag fields in summation at the given point, kinda how they can blast a gallstone with a bunch of focused sound waves.

what about overhead power lines, what else is around?

 

[mbrooke]

ok, so, ever been on the ghost tour in San Diego at Old Town? at one point he pulls out a special mag meter over a site that had some history, the thing goes crazy, says there are no utilities or odd piping around or underground.

so, it is possible that its just a matter of mag fields in summation at the given point, kinda how they can blast a gallstone with a bunch of focused sound waves.

what about overhead power lines, what else is around?

I see claimed magnetic fields from ghost hunters be amalgamated together with those of 50/60Hz wiring. My best guess if disinformation. For decades the link between man made electromagnetic fields and health effects like cancer has long been debated. Even if there is any conclusive evidence, its not something to convenient to be floating around in public.

The good news is its not difficult to dramatically reduce EMF or eliminate them altogether. For example, code complaint branch circuit wiring by itself has very, very low EMFs.