ETS-Lindgren HI-3627 ELF Magnetic Field Meter - Manual (Page 25)

HI-3627 Manual Page --17
Measurements must take this condition into account. It is
recommended when taking measurements in a room, the meter
be watched for a period of time to observe for fluctuations in
the indicated value of flux density. After some experience, it
may be possible to relate the observed fluctuations to various
uses of electricity within the home.
Residential Ground Currents
A phenomenon, which recently received attention in regard to
residential magnetic fields, is the flow of earth currents via
plumbing lines or telephone cables buried beneath the home. In
some cases, it has been noted that 60 Hz magnetic fields exist
within a home, even when the home is not using any electrical
power (the circuit breakers have all been turned off at the main
electrical service box of the home).
This observation has, in some cases, been related to the flow of
currents beneath the home on pipes or cables. It is not unusual
for currents related to other neighbors' use of electricity to flow
back to the electrical supply via low resistance paths. These are
formed by metal plumbing pipes or wires used for telephones as
opposed to the electrical system neutral wire. In such cases, it
is possible to measure magnetic flux densities within the home
even though the power to the home has been shut off.
Ground Faults
As mentioned earlier, current can exist in pipes and heating
ducts or anything metal in the house. This gives rise to an
interesting application for the HI-3627; detecting leakage
currents from appliances. For example it was noted that the
fields around a water pipe leading from a dishwasher changed
dramatically when the dishwasher was run. It was later found
that the dishwasher was defective and allowed excessive
ground currents to flow. The same principles apply to industrial
and power distribution situations.