SERVICING
29
CHECKING FOR PHASING - PRIMARY TO SECONDARY OF UNMARKED TRANSFORMERS*
If meter reads approximately 96 volts - the primary to secondary are in phase - if reads approximately 144 volts out of phase
- reverse low voltage wires.
*NOTE:
For flame rectification the common side of the secondary voltage (24 V) is cabinet grounded. If you were to bench
test a transformer the primary neutral and secondary common must be connected together for testing purposes.
Some transformers will display phasing symbols as shown
in the illustration to the left to assist in determining proper
transformer phasing.
Checking for polarization and phasing should become a
habit in servicing. Let's start now.
TRANSFORMER
.
SECONDAR
Y
PRIMAR
Y
.
GND
C
R
LINE VOLTAGE
L1 (HOT)
LINE VOLTAGE
(NEUTRAL)
METER READS
24 VOLTS
METER READS
120 VOLTS
.
GND
C
R
N
L1
.
GND
C
R
N
L1
READS 96 VOLTS - IN PHASE
READS 144 VOLTS - OUT OF PHASE
.
120.00
0.00
GND
GND
THIS IS L1 OR THE
HOT POWER LEG
THIS IS THE COMMON
OR NEUTRAL LEG
INCOMING POWER
These then should be wired to the furnace accordingly.
C
R
GN
D
NEUTRAL
L1
PHASING SYMBOL
24 V
120 V
