40
SERVICING
As more and more electronic's are introduced to the Heat-
ing Trade, Polarization of incoming power and phasing of
primary 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 phas-
ing 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:
THIS IS L1 OR THE
HOT POWER LEG
INCOMING POWER
THIS IS THE COMMON
OR NEUTRAL LEG
METER READS
120 VOLTS
METER READS
0 VOLTS
GN
D
GN
D
VOLT / OHM
METER
VOLT / OHM
METER
These then should be wired to the furnace accordingly.
Some transformers will display phasing symbols as shown
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.
.
. .
.
. .
VOLT / OHM
METER
G
N
D
PR
IM
A
R
Y
S
E
CO
NDA
RY
TRANSFORMER
R
C
METER READS
24 VOLTS
LINE VOLTAGE
(NEUTRAL)
LINE VOLTAGE
L1 (HOT)
VOLT / OHM
METER
METER READS
120 VOLTS
VOLT / OHM
METER
C
R
G
N
D
N
L1
VOLT / OHM
METER
READS 96 VOLTS - IN PHASE
C
R
G
N
D
N
L1
VOLT / OHM
METER
READS 144 VOLTS - OUT OF PHASE
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
G
N
D
NEUTRAL
L1
PHASING SYMBOL
24 V
120 V
