Important features of connecting a three-phase motor to a 220 or 380 V network

  • Dec 14, 2020
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Often, the owners of private houses install three-phase motors for solving various domestic needs: these can be small grinding machines, motors for grain threshers, concrete mixers, etc. But not all houses have industrial three-phase networks, most often these are more familiar 220 V.

How to connect a three-phase motor to a 380 V network

More modern electric motors provide only one type of connection - "star". Accordingly, only 3 outputs are provided in the junction boxes of such motors, all other connections are made directly in the case or on the motor windings themselves. If there are 6 pins, then you must first connect them correctly.

Important!To connect to a three-phase network, the motor windings must be delta-connected. Only then will the device work at full power.

Figure 1: Delta connection
Figure 1: Delta connection

How to correctly and quickly connect a three-phase motor to a 380 V network:

  1. Open the junction cover on the motor housing and bring in 3 phases there, having previously de-energized the line.
  2. Strip the wires and fasten each to its own winding with washers and nuts.
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  3. Check the quality of the contacts and close the cover. If necessary, apply a little sealant to the edges of the lid so that moisture does not penetrate there later.
  4. Start the motor energizing the windings.

If the motor shaft rotates in the opposite direction, then any 2 phases in the junction box should simply be reversed.

And if the network is single-phase (220 V)?

If the network is exclusively single-phase, then it is necessary to connect the windings in the motor junction box according to the "star" scheme, using standard jumpers for this. You should also purchase some additional elements: PNVS starter button, working and starting capacitors. In the absence of capacitors, the motor can only run without load.

Figure 2: Star connection

The sequence of connecting a three-phase motor to a 220 V network:

  1. On the upper terminals (1 and 2) of PNVS, fix the wires from the terminals of the starting capacitor.
  2. Fix the neutral wire of the network to the upper terminal (3) of PNVS.
  3. To the lower terminals (4, 5, 6) PNVS, bring 3 wires from the motor windings.
  4. To the lower terminals (4 and 5) PNVS also bring 2 wires from the working capacitor.
Figure 3: Illustrative connection diagram

Important! For technically correct and long-term operation, the capacity of the starting capacitor should be overestimated at least 3 times (in comparison with the working one).

Before installing capacitors on an electric motor, it is necessary to calculate their capacity. The formula for calculating the capacity of a working capacitor is quite simple:

Avg = 4800 * P (√3 * U (squared) * η * cos φ)

Where Cp is the capacity of the working capacitor, P is the motor power, U is the mains voltage, η is the efficiency of the motor, cos φ is the power factor.

Figure 4: Connecting a three-phase motor with a capacitor

To select the capacity of the starting capacitor, it is enough to multiply the calculated capacity of the working capacitor by 3. For motors up to 1.5 kW, one working capacitor in the circuit is sufficient.

For those who do not like to read, but love to watch and listen, I recorded a video where I spoke in as much detail as possible about how to properly connect a three-phase motor to a 220 or 380 Volt network. Happy viewing!