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Ohm
The derived unit for electrical resistance or
impedance; one ohm equals one volt per ampere.
Ohmmeter
An instrument for
measuring resistance in ohms. Take a look at this diagram to see how an
ohmmeter is used to check a small control transformer. The ohmmeter's
pointer deflection is controlled by the amount of battery current passing
through the moving coil. Before measuring the resistance of an unknown
resistor or electrical circuit, the ohmmeter must first be calibrated. If
the value of resistance to be measured can be estimated within reasonable
limits, a range selected that will give approximately half-scale deflection
when the resistance is inserted between the probes. If the resistance is
unknown, the selector switch is set on the highest scale. Whatever range is
selected, the meter must be calibrated to read zero before the unknown
resistance is measured.
Overcurrent
Any current in
excess of the rated current of equipment or the ampacity of a conductor. It
may result from overload, short circuit or ground fault.
Overload
Load greater than the
load for which the system or mechanism was intended. A fault, such as a
short circuit or ground fault, is not an overload.
Panelboard
A
single panel or group of panel units designed for assembly in the form of a
single panel: includes buses and may come with or without switches and/or
automatic overcurrent protective devices for the control of light, heat, or
power circuits of individual as well as aggregate capacity. It is designed
to be placed in a cabinet or cutout box that is in or against a wall or
partition and is accessible only from the front.
Peak Surge Current
The maximum current allowed for a single impulse with
continuous voltage applied.
Plenum
Chamber or space forming
a part of an air conditioning system
Polarity
The character of having magnetic poles,
or electric charges.
Potential
The amount of charge held by a body as
compared to another point or body. Usually measured in volts.
Power
Electrical energy measured
according to voltage and current (normally watts). Power in watts equals
volts times amperes for DC circuits. For single phase AC circuits, watts
equal volts times amperes times power factor.
Power Factor
Watts divided by voltamps (VA), KW
divided by KVA. Power factor: leading and lagging of voltage versus current
caused by inductive or capacitive loads, and 2) harmonic power factor: from
nonlinear current.
Propagation
The travel of an
electrical waveform along a medium. In other words, a surge passing along a
power cord to a system.
Protector
A protector is another
name for an arrester or diverter.
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