SERVICING
32
As more and more electronic's are introduced to the Heating
Trade, Polarization of incoming power and phasing of pri-
mary to secondary voltage on transformers becomes more
important.
Polarization has been apparent in the Appliance industry
since the introduction of the three prong plug, however, the
Heating Industry does not use a plug for incoming power,
but is hard wired.
Some of the electronic boards being used today, with flame
rectification, will not function properly and/or at all without
polarization of incoming power. Some also require phasing
between the primary and secondary sides of step-down
transformers.
We recommend that these two items be checked during
normal installation and/or service calls. See as follows:
120.00
0.00
GND
GND
THIS IS L1 OR THE
HOT POWER LEG
THIS IS THE COMMON
OR NEUTRAL LEG
INCOMING POWER
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.
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
.
These then should be wired to the furnace accordingly.
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.
C
R
GN
D
NEUTRAL
L1
PHASING SYMBOL
24 V
120 V
