MEASUREMENTS - STARTING LAMP VOLTAGE
Typical Two-Lamp RS Ballast
MAINTENANCE & REPAIR 63
Starting Voltage
The largest percentage of light ballasts used today
are of the two-lamp Rapid Start type. In order to read
starting or open circuit voltage, as it often called,
remove both lamps from their sockets. The high volt-
age (OVC) which starts and operates the lamp is
always between the “R” and “B” sockets. The two
lamps are in series between these sockets. The Y-1
and Y-2 connections provide cathode heat, and serve
to connect the lamp ends together. Because the
leads between Y-1 and Y-2 are connected together by
jumper leads, they are always wired to sockets at
one end of the fixture. Therefore, the “R” and “B”
sockets are always at the other end of the fixture.
This means that in order to measure the voltage
which starts the lamps (OVC), the meter probes must
be placed in the sockets at one end of the fixture.
The Y-1 and Y-2 end of the fixture will read zero while
the “R” and “B” end of the indoor ballast should read
as follows:
Min. RMS Min. RMS Min. RMS
Lamp Type Voltage HO Voltage 1500 MA. Voltage
F40 256 48" 256 48" 250
F30 215 72" 395 72" 350
96" 465 96" 470
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