Ingersoll-Rand ReliaTel, Manual, Page: 160 / 176

160 RT-SVD03L-EN
Transformer Troubleshooting
The graph shows how as current caused by loads on
the transformer increases, voltage decreases. Once the
voltage drops below the level that the contractor can
pull in, usually about 16-18 volts, the current raises up
to the point where the transformer burns out. The chart
below is for illustration only.
A transformer usually burns out due to a short circuit.
When this occurs, the technician can usually find the
source of the short.
Sometimes though, the cause of transformer failure is
not so obvious. It can also fail when excessive voltage
drops occur because of poor connections, thermostat
wires too long, bad contacts on the smoke detector,
etc.
The excessive voltage drop results in low voltage to the
load (contactor, relay) and then the transformer blows.
Here’s what to look for:
• Transformer on the wrong voltage tap, i.e. 208 volts
at the unit, transformer on the 230 volt tap.
• Voltage drop across contacts (measure with a load
on the circuit): Voltage drop across contacts when
load is applied should be less than ½ volt.
Figure 101. Transformer chart
208/240 Volts Primary 60 Hertz
Second
ar
y V
olt
ag
e
(A
C)
Secondary Amperes
240 V
208 V
Figure 102. Transformer troubleshooting
0.3 VAC
AC
Volts