INTRODUCTION
GLOSSARY OF TERMS
(as used in this manual)
Alternating Current, AC: Current which reverses direction on a regular basis, commonly in the
U.S.A. 60 times per second, in other countries 50 times per second.
Breakdown: The failure of insulation to effectively prevent the flow of current, sometimes evident by
arcing. If voltage is gradually raised, breakdown will begin suddenly at a certain voltage level. Current
flow is not directly proportional to voltage. Once breakdown current has flown, especially for a period of
time, a repeated application of voltage will often show breakdown beginning at a lower voltage than
initially.
Conductor: A solid or liquid material which has the ability to let current pass through it, and which has
a volume resistivity of no more than 10
3
ohm-cm.
Current: The movement of electrons through a conductor. Current is measured in amperes,
milliamperes, microamperes, nanoamperes, or picoamperes. Symbol = I
Dielectric: An insulating material which is positioned between two conductive materials in such a way
that a charge or voltage may appear across the two conductive materials.
Direct Current, DC: Current which flows in one direction only. The source of direct current is said
to be polarized and has one terminal which is always at a higher potential than the other.
Insulation: Gas, liquid or solid material which has a volume resistivity of at least 10
12
ohm-cm and is
used for the purpose of resisting current flow between conductors.
Leakage: AC or DC current flow through insulation and over its surfaces, and AC current flow through
a capacitance. Current flow is directly proportional to voltage. The insulation and/or capacitance is
thought of as a constant impedance, unless breakdown occurs.
Measuring Device (MD): A resistive and capacitive network used to simulate the impedance of the
human body during Line Leakage testing.
Resistance: That property of a substance which impedes current and results in the dissipation of power
in the form of heat. The practical unit of resistance is the ohm. Symbol = R
Trip Point: The minimum current flow required to cause an indication of unacceptable performance
during a dielectric voltage-withstand test.
Voltage: Electrical pressure, the force which causes current through an electrical conductor.
Symbol = V
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