ML0030 August 2009 Copyright 2009 Bitronics, LLC
−
8
−
3.6 Surge Protection
It is recommended that a metal oxide varistor (MOV) be placed across the power supply
inputs to protect the meter in the event of high voltage surges or lightning strikes.
WATT/VAR meters are shipped with a transient suppression network already attached as a
standard design. The MOV provides an added measure of protection against heavy
switching transients occasionally experienced in the field. The MOV is designed to clamp
applied power voltages above 170V ac RMS (270 V ac RMS for 220V instruments). A
single MOV protects the meter Line to Line, and two high voltage capacitors are provided to
protect each Line to Ground.
To avoid damaging the MOV protectors, maintain continuously applied power voltages
within the ratings of the instrument. The GREEN lead of the MOV assembly should be
connected to a good earth ground. In most instances, this is usually accomplished by
connecting the GREEN lead to the indicated front mounting stud. This mounting stud is
a safety ground for the instrument, and should be connected to a protective earth circuit
(refer to Figure 3). Although the Line to Ground capacitors are 3kV and UL rated, users
of DC powered instruments may wish to eliminate the Line to Ground protection, these
users may do so by clipping the GREEN lead at the MOV board and discarding the
GREEN lead. Mounting of the MOVs external to the instrument allows easy access so
that the MOVs may be readily inspected for damage. If the unit is to be powered from a
PT, it is recommended that one side of the PT be grounded at the instrument following
ANSI/IEEE C57.13.3-1983. The MOV board voltage rating is indicated on the MOV
board, and must match the voltage supply rating of the instrument.
Figure 3 - Outside Dimensions
