No electrical ground or conduit to ground is perfect in that the ground wire is able to immediately sink an indefinite amount of charge such that it remains at a constant potential. Appliances and equipment that use electrical energy in a periodic or pulsed manner will conduct an oscillatory surge of electrical charge through their mechanisms on their way to electrical ground. These pulses of current will cause the local electrical ground to oscillate away from neutral with the same periodicity as the current flow through the device. There can be many such appliances operating at the same time resulting in a ‘noisy’ ground. A measure of such noise contributions is known as ‘dirty electricity’.
Bad mains AC wiring can create large magnetic field loops in such instances where a paired ground wire has been omitted and ground is made through another route; by teaming up with another ground wire, or even using the metal pipe plumbing. Such practises might save on the extra expense for a proper ground wire, but taking short cuts can easily be hidden since such cabling is usually covered behind walls. floors, ceilings and attics.
There is also the new technology which places a microwave frequency on the mains as a means of providing internet connectivity through the power mains wiring network. See Dirty Electricity.
Electrical wiring errors can be common source of excessive magnetic fields and are usually reparable by a licensed electrician.
Wiring errors, such as connecting the neutrals/return wiring of 2 different branch circuits (also known as “ganged neutrals” or “paralleled neutrals”), can create large areas of high AC magnetic fields, which decrease linearly with distance, unlike point sources that decrease with the square or cube of the distance. Another common error is making neutral to ground connections outside of the main service panel. By creating multiple return paths for the return current, this causes some of the return current to travel on an unintended path, causing a deficit on the intended path and a surplus on the unintended parallel path. If there is net current on any cable (current on hot/supply and neutral/return wires do not cancel), then the strength of the magnetic field may be high, and decrease linearly with the distance rather than with the square of the distance. The resulting magnetic fields may be ranging over a wide area and may be higher than living near an electricity tower.
Wiring errors should be corrected by a licensed electrician. In some cases, due to wiring code violations, there can be larger regions with high EMF in a home or office.