electric magnetic fields

electric and magnetic fields

Electric and magnetic fields (EMF) are produced wherever electricity or electrical equipment is in use.

EMFs in and around the home are produced by anything with electric current flowing through it, such as powerlines running from the street to your home, the home wiring system and electrical appliances. Most household appliances operate on 240 volts, so electric fields are low.

In the workplace, electric fields and magnetic fields may be produced by nearby powerlines, factory machinery, computers, lights, photocopiers, electrical cabling, etc.

Electric and magnetic fields in and around the home can be produced by anything with electric current flowing through it, including nearby powerlines, your home wiring system or electrical appliances in use in the home. However, generally, powerlines contribute little to the electrical fields that can be measured inside a house or office. This is because the walls of the building, in fact any solid object, create a shield from the electrical field. A typical house generally shields at least 90% of the electrical fields from outside.

magnetic fields from powerlines

Both high voltage lines and distribution lines produce magnetic fields. In many cases, high voltage lines are constructed on easements where building is not permitted.

Magnetic fields associated with powerlines depend on the amount of current flowing along the line and the distance from the line. Fields rapidly decrease in strength with distance, therefore inside a house, magnetic fields from nearby powerlines is usually similar to that from wiring and appliances.

The following table shows typical magnetic field strengths from a number of common sources, including powerlines. Fields are measured in a unit 'milligauss'. To give you an idea of the relative strength of EMFs, the following guide shows the typical magnetic fields from appliances and under powerlines.

	common sources of EMF		typical measurement (in Milligauss)		range of measurements (in Milligauss)
	Electric stove		6		2-30
	Personal computer		5		2-20
	Television		1		0.2-2
	Electric blanket		20		5-30
	Hair dryer		25		10-70
	Fridge		2		2-5
	Toaster		3		2-10
	Kettle		3		2-10
	Pedestal fan		1		0.2-2
	Distribution powerlines (under line)		10		2-20
	Distribution powerlines (8 metres away)		2		0.4-4
	33 kV underground cables (directly above buried cable)		12 (1 metre above ground)		3 (4 metres away)
	Pad mounted distribution transformer		2 (at 5 metres)		1-20 (10 metres to close up)
	Major zone substation		2 (at substation fence)		1-6 (at substation fence)
	Modular substation		1.5 (at substation fence)		0.5-3 (at substation fence)
	Transmission powerlines (under line)		20		10-200
	Transmission powerlines (at edge of easement)		10		2-50