Regarding the below nameplate of an induction motor:

enter image description here

What is meant by?:

Δ/Y 220/380

Does that mean if delta connected the line to line voltage must be 220V? Im confused also because isnt 220 phase voltage and 380 lne voltage? Could you explain this question with diagram?

  • 1
    \$\begingroup\$ The motor can be configured to run on different voltages by changing the way its windings are connected internally. If it's delta-connected, it needs a 220 volt three-phase line-to-line voltage, whereas if it's wye-connected, it needs a 380 volt three-phase line-to-line voltage. \$\endgroup\$ – Hearth Mar 13 '19 at 18:07
  • \$\begingroup\$ But where on earth line to line is 220V? In USA it must be sqrt(3)*220 = 190V and in Europe is 380V. Where do you think 220V line to line come from? \$\endgroup\$ – user1999 Mar 13 '19 at 18:13
  • 2
    \$\begingroup\$ Actually, the common industrial three-phase voltages here in the US are 120V/208V, 230V/400V, 240V/415V and 277V/480V. There are supposedly also 347V/600V systems, but I've never seen one. \$\endgroup\$ – Hearth Mar 13 '19 at 18:18
  • 1
    \$\begingroup\$ @Hearth We use 347/600V in Canada. It's commonly found in places where you would se 277/480V in the US. I don't think anywhere in the US uses 347/600V. \$\endgroup\$ – J... Mar 13 '19 at 18:55
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    \$\begingroup\$ Many variable frequency drives put out 220V delta, especially the smaller ones where the input is single phase. I don't know how common such would be at that size but this is sometimes very useful in applications like retrofitting smaller machine tools with a VFD to run on single phase input to the drive. \$\endgroup\$ – Dan Mills Mar 14 '19 at 10:51


simulate this circuit – Schematic created using CircuitLab

Figure 1. Two connection methods.

The windings on your motor can take 220 V between their terminals.

  • On a 220 V 3-phase supply you connect as shown in Figure 1b.
  • On a 380 V 3-phase supply you connect as shown in Figure 1a.

Note that in each case the voltage across each winding is 220 V while the voltage between the supply terminals may not be.

It is simple trigonometry to show that the 380 V phase to phase voltage is \$ \sqrt 3 V_{p-n} \$.


If you take the ratio of line voltage to the phase voltage for a 3 phase system supply you get \$\sqrt3\$ = 1.732. Now 380 divided by 220 is 1.727 (about 0.3% off from perfect) so this informs that if the windings are Y connected, each winding receives 220 volts from a 380 volt 3 phase supply.

Try this picture of a 120 volts/208 volt set-up: -

enter image description here

  • \$\begingroup\$ Oh I got it very clear now thanks. \$\endgroup\$ – user1999 Mar 13 '19 at 18:18
  • \$\begingroup\$ But dont you think they wrote in wrong order on the name plate? \$\endgroup\$ – user1999 Mar 13 '19 at 18:20
  • \$\begingroup\$ They wrote Δ/Y 220/380 but shouldnt it be more correct Δ/Y 380/220 ?? \$\endgroup\$ – user1999 Mar 13 '19 at 18:21
  • \$\begingroup\$ No, if you operate in delta your line voltage is 220 volts because the coils are placed directly across pairs of lines. In star, to get the same 220 volts across each winding, you have a line voltage of 380 volts. \$\endgroup\$ – Andy aka Mar 13 '19 at 18:21
  • \$\begingroup\$ Hmm I guess I need to think about it more \$\endgroup\$ – user1999 Mar 13 '19 at 18:22

It is actually quite simple.

It the nameplate states Δ/Y 220/380 this means that this motor is designed and can be connected in delta, if the line voltage is 220 volts. If the line voltage is 380 V then the motor can be connected in star.

This comes from the fact, that the the max allowed voltage per motor winding is 220 volts. In either case the the winding gets 220 volts supply. By connecting this type a motor in delta with line voltage 380 will burn the motor!

When the line voltage is 380V and you want to connected it to delta then the motor nameplate should state Δ/Y 380/660.


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