3.0 Electrical Parts and Controller Design Considerations
3.1 Selection of Electrical Wiring
Voltage drop may occur due to the large current draw during compressor starting. The starting failure will
occur if the starting voltage is under the range of compressor specifications. So it is necessary to select the
proper size of electrical wire.
3.1.1 Voltage Drop
See Figure 3-1 for the explanation of voltage drop.
a) Set Voltage:
The voltage applied to compressor terminals before compressor is started.
b) Starting Voltage:
The voltage applied to compressor terminals when compressor is being started. When compressor
is starting, the big starting current will cause the drop of voltage. It will be very hard to start
compressor if the starting voltage is too low.
c) Running Voltage:
The line voltage applied to compressor terminals when compressor is running stably. This running
voltage is a little lower than set voltage.
The big voltage drop happens in compressor starting process, it will cause the failure of starting if
the starting voltage is lower than 85% of rated voltage.
Figure 3-1 Voltage Drop During Compressor Starting