138 RT-SVD03G-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.
Transformer Troubleshooting
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 81. Transformer Chart
Figure 82. Transformer Troubleshooting
208/240 Volts Primary 60 Hertz
Secondary Voltage (AC)
Secondary Amperes
240 V
208 V
To Next Page
Loading...
