E

Earth (Ground) - Any zero-voltage point. The earth itself is taken as being of zero voltage because its potential is not greatly affected by small currents. Conductors that connect equipment or circuits to earth or to an earth network are often referred to as earth.

Earth electrode - A conductor or group of conductors providing a good electrical connection the Earth (soil).

Earth leakage current - A stray current that flows to earth, in a circuit that is electrically sound. For safety reasons, the earth leakage current must be kept within prescribed limits.

Earth potential - Normally zero voltage

Earth reference - Connection to earth.

ECMA - Abbreviation for European Computer Manufacturers Association

Electric field - The field of force surrounding a charged object

Electrical noise - A signal frequency that may be riding on top of the power line sine wave. A number of systems use the power lines to carry signals and data to other locations. Attempts to filter out the "noise" may disrupt the current or future operation of these systems. Although it is seldom needed, it is wiser to provide line conditioning filtering immediately in front of sensitive equipment.

Electromagnetic compatibility (EMC) - A philosophy referring to attempts to prevent EMI. EMC practice dictates that potential sources of interference are designed so as not to affect equipment, and that potential victim equipment is designed to be immune from potential sources of interference.

Electromagnetic field - Combined electric field and magnetic field

Electromagnetic interference (EMI) - Electrically induces noise or transients

Electromagnetic pulse (EMP) - Pulses of energy caused by nuclear explosions and intense solar activity. EMP transients are much quicker (a faster rise time) than commonly occurring transients. Also called nuclear electromagnetic pulse (NEMP).

Electrostatic discharge (ESD) - Unlike NEMP or EMP, electrostatic discharge does not tend to be transmitted on power or data lines. An electrostatic charge is generated by two insulating objects being rubbed together. A charged object will discharge when it comes into contact with a conducting object.

EMC - Abbreviation for electromagnetic compatibility

EMI - Abbreviation for electromagnetic interference

EMP - Abbreviation for nuclear electromagnetic pulse

Energy - Maximum allowable energy (in joules) for a single impulse on a 10/1000 µs current waveform. Indicative of the maximum amount of energy that the suppressor can dissipate. This energy is dependent upon three variables: Voltage, Current, and Time. Any variation of the three will affect this figure.

Equipment transient design level - Term used in BS 6651:1992 to refer to the level at which a piece of equipment becomes susceptible to interference from transient overvoltages.

Equipotential - Of equal potential. This term is often used when describing a low resistance connection or bond between equipment and earth, made to ensure that the two points are always at the same voltage.

ESD - Abbreviation for electrostatic discharge

ETDL - Abbreviation for equipment transient design level

Ethernet - This is the product name of a particular form of local area network. It is governed by the standard IEEE 802.3 and operates over distances of up to around 2.5 km. Originally based upon a coaxial cable, the system can now also utilize twisted pair and fiber optic cable.