From this question we can see these parameters:
1. There are three heating tubes;
2. The rated voltage of each heating tube is 220V;
3. The power supply voltage they want to connect is 380V;
We know that there are 4 commonly used wiring methods for heating tubes:
1. Tandem
When connected in series, the total voltage of the heating tube is equal to the sum of the voltages of each phase, then the total voltage of the three 220V heating tubes is 220*3=660V, which is not suitable for this wiring method.
2. Parallel
When connected in parallel, the total voltage of the heating tube is equal to the voltage of each phase, so the total voltage of the three 220V heating tubes is also 220V, and obviously it is not possible to connect to the 380V power supply.
3. Triangular wiring method
In this wiring method, the total voltage of the heating tube is equal to the phase voltage, so three 220V electric heating tubes should be connected to a 220V power supply voltage.
3. Star (Y) wiring method
When using the star connection method, the total voltage of the heating tube is equal to the voltage of each phase * 1.732, and the three 220V heating tubes should be 220 * 1.732 equal to about 380.
Through the analysis of the above wiring methods, it can be seen that three 220V heating tubes connected to the 380V power supply should use the star connection, while a single 220V heating tube can only be connected to the 220V power supply, not to the 380V power supply.