Magnetic field strength:
- is directly related to the amount of current flowing, and
- diminishes rapidly with distance from an electrical source.
Magnetic fields are measured in units of gauss (G) or milligauss (mG). Gauss is the unit most commonly used in Canada, while tesla is more commonly used internationally. Most magnetic fields related to electrical devices are only a fraction of a gauss so it is more common to measure magnetic fields levels in units of milligauss (mG). A milligauss is 1/1000 of a gauss.
Sources of Magnetic Fields
Electric and magnetic fields are anywhere that electricity is flowing. Two commons sources of magnetic fields are electrical appliances and power lines.
Electrical Appliances
Magnetic field strength from appliances depends on the current flowing through the appliance, the configuration of the wiring within the appliance, and a person's distance from the appliance. Due to proximity, the magnetic fields produced by appliances are often much higher than those produced by power lines; however, the levels fade quickly as you move away from an appliance.
Power lines
Just like appliances, the magnetic field levels from power lines depend on the amount of current flowing on the line, the configuration of the circuit and the distance from the line.
The current or electrical load on a power line will depend how much electricity is being used at any given time. In British Columbia varations in electrical load follow a fairly typical pattern, with morning and evening peaks, and larger loads in the winter months than during the summer.
Magnetic fields diminish rapidly with distance, so as you move away from a power line the magnetic field strengths drop off quickly.