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Issue: #TB107.1
Date: September 1, 2005
Topic: Inrush Information
Technical Bulletin
Watt Stopper/Legrand 2800 De La Cruz Blvd Santa Clara CA 95050
800.879.8585 www.wattstopper.com
FOR GENERAL DISTRIBUTION
Electronic Ballasts and Inrush Current
Inrush current caused by electronic ballasts is an important
factor in determining the long term reliabilityof lighting systems.
When considering the operational life span of automatic wall switch
sensors or powerpacks, one of the most commonly affected components
is the relay. Inrush current can overwhelm thecurrent capacity of a
relay, fusing the contacts over time and leaving the switch
permanently ON. Not only
is inrush capable of damaging the relay, but also other
components of a lighting system.
What is inrush current?
Inrush current occurs when a ballast is first switched on. It is
always much higher than the normal oper-ating current, at times 100
or more times the operating current. Electronic ballasts are the
principalcause of this current, and the level of inrush current
depends on the form of power factor correction. Allelectronic
ballasts contain large capacitors to store energy that help provide
the lamp with a constant sup-ply of energy. When the switch is
turned on, the capacitor pulls current from the line to charge
itself,causing inrush current to occur.
Electronic ballastsElectronic ballasts come in different
configurations. There are two high power factor corrected
ballasts:
active and passive. Both of these types of ballasts require
current to charge the capacitor, however, thedifferent values of
their respective circuit components yield different levels of
inrush current. Active powerfactor ballasts tend to require levels
of inrush current that can be potentially damaging to a relay and
thelighting system. Passive power factor ballasts have larger
inductors and do not cause high levels ofinrush. Due to their large
inductors, they are prone to transient voltage arcing that occurs
at switch-off,which can cause damage to the insulation and
potentially, the components of the ballast.
Effects of inrush current
Watt Stoppers zero crossing circuitry provides a solution to the
problem of inrush current by making surethat switching occurs at or
near zero voltage. At zero voltage, the AC current in ballasts is
not at its peak(90 phase). Switching when voltage is at or near
zero protects the relays in occupancy sensors and powerpacks, which
in turn extends their operating life. Zero crossing circuitry, by
enhancing reliability andreducing stress on other lighting system
components, provides a comprehensive solution to the problemsof
inrush current.
The effects of inrush extend to many elements of the lighting
system. For example, the relay of a wallswitch is generally not
capable of handling high levels of inrush current. Often, relays
are rated to handleonly 10 times the normal operating current, not
the extremely high levels of inrush current associatedwith
electronic ballasts (i.e., up to 100 or more times the normal
operation current). Relay contacts can
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fuse from repeated exposure to these high levels of inrush
current.
Watt Stoppers zero crossing circuitry provides a solution to the
problem of inrush current by making sure
that switching occurs at or near zero voltage. At zero voltage,
the AC current in ballasts is not at its peak (90
phase). Switching when voltage is at or near zero protects the
relays in occupancy sensors and power packs,which in turn extends
their operating life. Zero crossing circuitry, by enhancing
reliability and reducing stress
on other lighting system components, provides a comprehensive
solution to the problems of inrush current.
Watt Stopper/Legrand Technical BulletinIssue: #TB107.1 Date:
September 1, 2005
Watt Stopper/Legrand 2800 De La Cruz Blvd Santa Clara CA 95050
800.879.8585 www.wattstopper.com
Inrush Current at 90Phase Angle
30
20
10
Amps
Actual Ballast Measurement - 2 Lamp, 277V
35.4A at approx. 400V
2 4 6 8
msec
