230/400 V vs 400/690 V Motors: Which Voltage Should You Buy?

On Türkiye’s 400 V (formerly 380 V) supply both 230/400 V and 400/690 V motors run; the difference is the connection: a 230/400 V motor is connected in star, a 400/690 V motor in delta. When buying, the starting method decides: if your panel has star-delta starting, or will have it, choose a 400/690 V motor; with direct-on-line, a soft starter or an inverter with 3×400 V output, either can be used.

On paper this looks like a minor detail, but a motor with the wrong nameplate either does not fit the panel or is connected wrongly and burns out. Changing the terminal links, connecting the cables and the first start must be done by a qualified electrician with the panel isolated; this article explains the decision before ordering, it is not a wiring instruction.

DRG Motor is a manufacturer, supplier and seller of electric motors. The nameplate voltage and 400 V connection of each of the 120 models on the Buy Electric Motors Online page are stated on its product page; with the decision table below you can settle which one you need before ordering.

Which voltage should I choose? Decision table

Read the table against your own panel: left column is the current situation, middle column the motor to buy, right column the reason.

In short: for every plant with a star-delta panel the answer is 400/690 V. If the panel has only one contactor and an overload relay (direct-on-line), use whichever nameplate the DRG model of your power comes with.

What do the two voltages on the nameplate mean?

Each phase winding of a three-phase motor is wound for a given voltage. The smaller number on the plate is the voltage the winding withstands, and with the windings in delta the motor runs on that line voltage; the larger number is the line voltage for star connection (√3 times the smaller one).

• 230/400 V: 230 V winding. Delta on a 230 V supply, star on a 400 V supply.
• 400/690 V: 400 V winding. Delta on a 400 V supply, star on a 690 V supply.
• Common point: on a 400 V supply the two motors do not see the same voltage per winding while running; the 230/400 V motor sees ≈231 V (400/√3), the 400/690 V motor sees 400 V — each its own winding voltage.

How the terminal links are fitted and the connection by kW are detailed in our article which kW motor is connected in star or delta; here the topic is which nameplate to ask for when buying.

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From which power do DRG models become 400/690 V?

Of the 120 models in the DRG store, 43 are 230/400 V and 77 are 400/690 V. The limit is clear by power: all models from 0.25 kW to 3 kW are 230/400 V, all models of 4 kW and above are 400/690 V. The models on either side of the limit:

Between 3 kW and 4 kW the nameplate changes whatever the number of poles. If you need star-delta starting at 3 kW or below, talk to us before ordering; at these ratings direct-on-line, a soft starter or an inverter is usually preferred. Currents for other ratings are in the motor current chart.

Why does star-delta starting require a 400/690 V motor?

With star-delta starting the motor first starts in star, then after a few seconds switches to delta and keeps running. Because the running connection is delta, the motor must be connectable in delta on 400 V, i.e. be 400/690 V. At start the winding voltage drops by √3, and current and torque fall to about one third. Calculation with the 7.5 kW 4-pole DRG-132M-4:

• Direct starting current: 14.3 A × 7.5 ≈ 107.2 A
• Starting current in star: 107.2 / 3 ≈ 35.8 A
• Direct starting torque: 49.1 Nm × 2 ≈ 98.2 Nm
• Starting torque in star: 98.2 / 3 ≈ 32.7 Nm (about two thirds of rated torque)

Result: in star the starting torque falls below rated torque. That is enough for fans, pumps starting unloaded or drives with slack belts; a conveyor starting with a full belt or a crusher starting under load may not accelerate in star. If the load starts under load, compare other starting methods with the starting methods and star-delta calculator instead of star-delta. Values used in the calculation:

• Model: DRG-132M-4
• Power: 7.5 kW
• Rated speed: 1460 rpm
• Nameplate voltage: 400/690 V (Δ/Y)
• Connection at 400 V: Δ (delta)
• Current at 400 V: 14.3 A
• Is/In: 7.5
• Rated torque: 49.1 Nm
• Ts/Tn: 2

What happens if you buy the wrong nameplate?

The two most common mistakes are buying a 230/400 V motor for a star-delta panel and connecting a 400/690 V motor in star “because the old one was in star”. The table shows the results on a 400 V supply.

The mistake in the second row is silent: the motor turns and looks normal unloaded, but since the winding sees ≈231 V instead of 400 V, torque drops to about (230/400)² ≈ 0.33. Under load the speed drops, current rises and the overload trips or the motor overheats. Photograph the nameplate before connecting the new motor and have your electrician wire it according to the plate.

Which voltage for a motor running on an inverter?

The inverter output voltage determines the winding connection. With a 3×400 V output (three-phase input) inverter, a 230/400 V motor is connected in star and a 400/690 V motor in delta; both deliver full power. There is no star-delta requirement here because the inverter does the starting.

With a 3×230 V output (single-phase input) inverter, only a 230/400 V motor connected in delta delivers full power; a 400/690 V motor cannot reach its rated power on that output. The inverter current rating must not be lower than the motor’s nameplate current at that voltage. If you may later move the same motor to a 3×400 V output inverter or directly to the mains, a 230/400 V motor keeps that flexibility: only the terminal links are changed from delta to star.

Checklist before ordering

• Have the supply line voltage measured (400 V, 690 V or 230 V three-phase?).
• Identify the starting method in the panel: direct, star-delta, soft starter, inverter.
• In a star-delta panel check the motor cables: two separate three-core cables (6 ends) go to the motor.
• Photograph the voltage and connection on the old motor’s nameplate.
• Fix power and speed; remember the nameplate changes between 3 kW and 4 kW.
• If there is an inverter, read its output voltage and rated output current from its label.
• Is there a start under load? If so, account for one third torque in star.
• Have a qualified electrician connect the new motor’s terminals according to the nameplate.

Motors in this power range

2- and 4-pole cast iron models on either side of the 230/400 V – 400/690 V limit:

• DRG-100L-2 – 3 kW – 2895 rpm – 100L cast iron
• DRG-100L2-4 – 3 kW – 1450 rpm – 100L cast iron
• DRG-112M-2 – 4 kW – 2905 rpm – 112M cast iron
• DRG-112M-4 – 4 kW – 1450 rpm – 112M cast iron
• DRG-132S-4 – 5.5 kW – 1460 rpm – 132S cast iron
• DRG-132M-4 – 7.5 kW – 1460 rpm – 132M cast iron

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Frequently Asked Questions

How is a 400/690 V motor connected on 380 V?

On a 380–400 V supply a 400/690 V motor is connected in delta. In star the winding sees ≈231 V and the motor is too weak under load.

Can a 230/400 V motor be star-delta started?

Not on a 400 V supply. In star-delta the running connection is delta, and a 230/400 V motor in delta on 400 V sees about 1.74 times its winding voltage (400/230). Star-delta needs a 400/690 V motor.

From how many kW is a motor 400/690 V?

In the DRG store all models up to 3 kW are 230/400 V, and all models of 4 kW and above are 400/690 V.

Does a 400/690 V motor draw more current?

No. On a 400 V supply the line current of a motor of the same power does not depend on the nameplate voltage; only the winding connection differs. Current depends on power, speed and cos φ.

You can send the nameplate photo and your panel details to +90 (542) 666 11 11 or [email protected]; all channels are on our contact page. For all models with their voltages and current prices, see Buy Electric Motors Online.