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When connecting a 3 kW motor to a gearbox, the deciding dimension is the gearbox input bore: the 2- and 4-pole 3 kW motors (DRG-100L-2, DRG-100L2-4) sit in the 100L frame with a 28 mm shaft and a B5 flange with a 180 mm spigot, while the 6-pole DRG-132S-6 moves to the 132S frame and needs a 38 mm input bore, 230 mm spigot and 265 mm bolt circle on the gearbox. If the gearbox input is machined for a 100 frame, the 132S motor will not fit.
So before ordering, read the IEC input size on the gearbox nameplate or catalogue and select the motor accordingly; speed comes second. All 3 kW models and their housing options are on the Buy Electric Motors Online page.
The list also includes a compact option: the cast iron DRG-90L-2K delivers 3 kW at 2 poles from a 90L frame, with a 24 mm shaft and a flange with a 130 mm spigot. If a gearbox with a small input flange needs 3 kW at 3000 rpm, this model may be suitable.
Matching table: 3 kW motors by gearbox input
The table shows the dimensions each motor presents to the gearbox and the output speed it gives on a 1/20 gearbox. Dimensions come from the B5 flange table of the DRG catalogue; speed and torque values come from the product data.
| Motor | Frame / housing | Gearbox input bore (D) | Key F / shaft length E | Spigot N / bolt circle M | Rated torque | Output speed at i = 20 | Price |
|---|---|---|---|---|---|---|---|
| DRG-100L-2 | 100L / aluminium | 28 mm | 8 / 60 mm | 180 / 215 mm | 9.9 Nm | 144.8 rpm | See Prices |
| DRG-100L2-4 | 100L / aluminium | 28 mm | 8 / 60 mm | 180 / 215 mm | 19.8 Nm | 72.5 rpm | See Prices |
| DRG-132S-6 | 132S / aluminium | 38 mm | 10 / 80 mm | 230 / 265 mm | 29.6 Nm | 48.4 rpm | See Prices |
| DRG-90L-2K | 90L / cast iron | 24 mm | 8 / 50 mm | 130 / 165 mm | 9.9 Nm | 144.8 rpm | See Prices |
The 100L and 132S flanges seen from the gearbox side
Put the two B5 flanges side by side and the difference is not only the diameter:
- 100L: P 250 mm, M 215 mm, N 180 mm, S 14.5 mm, T 4 mm, LA 13 mm; shaft 28×60, key F 8 mm, key base G 24 mm, shaft end M10X22.
- 132S: P 300 mm, M 265 mm, N 230 mm, S 14.5 mm, T 4 mm, LA 14 mm; shaft 38×80, key F 10 mm, G 33 mm, shaft end M12X28.
Because hole diameter (S) and spigot depth (T) are the same on both frames, it is easy to assume the flange fits by looking only at the bolts. Yet the 132S shaft is 20 mm longer (80 against 60 mm); on a hollow-input gearbox the shaft may bottom out in the input bore. Compare the input depth of the gearbox with the shaft length E.
Output speed and torque: which pole count for which job?
Gearbox output speed equals motor speed divided by the ratio (i); output torque, apart from losses, is motor torque multiplied by i. For three ratios the result is (lossless, approximate):
- DRG-100L-2 (2895 rpm, 9.9 Nm): i = 10 → 289.5 rpm and 99 Nm; i = 20 → 144.8 rpm and 198 Nm; i = 40 → 72.4 rpm and 396 Nm.
- DRG-100L2-4 (1450 rpm, 19.8 Nm): i = 10 → 145 rpm and 198 Nm; i = 20 → 72.5 rpm and 396 Nm; i = 40 → 36.2 rpm and 792 Nm.
- DRG-132S-6 (968 rpm, 29.6 Nm): i = 10 → 96.8 rpm and 296 Nm; i = 20 → 48.4 rpm and 592 Nm; i = 40 → 24.2 rpm and 1184 Nm.
As you can see, the 2-pole motor with i = 20 and the 4-pole motor with i = 10 give the same output speed and torque. This is why 4-pole motors are common on gearboxes: with a lower input speed the gearbox runs quieter and the oil heats less. Use a 2-pole motor only if the gearbox maker allows that input speed. Real output torque is lower by the gearbox losses; try the values with your own ratio in the gearbox output speed and torque calculator.
When does a 6-pole 3 kW motor make sense?
On jobs that need a very low output speed (around 25 rpm, for example) such as conveyors, mixers or turntables, a 6-pole motor reduces the gearbox ratio: a speed that needs about i = 58 with 4 poles is reached at about i = 40 with 6 poles. This may allow a single-stage or smaller gearbox.
The price is the frame: DRG-132S-6 comes in the 132S frame with a 6208-ZZ-C3 bearing and 2 × M32×1.5 cable entries, and its overall length is 438 mm (406 mm on the 100L frame). The gearbox input must also suit a 132 frame. Electrically it draws 7.2 A at 380 V with cos φ 0.74; on the 4-pole model these values are 6.34 A and 0.82.
Electrical connection and starting
All four 3 kW models are wound for 230/400 V; on a 380 V three-phase supply they are star (Y) connected. With geared loads, starting usually happens under load. Using the Is/In ratios, approximate starting currents at 380 V are: 6.02 × 7.8 ≈ 47 A for DRG-100L-2 and DRG-90L-2K, 6.34 × 7.6 ≈ 48.2 A for DRG-100L2-4 and 7.2 × 6.8 ≈ 49 A for DRG-132S-6. The starting torque ratio Ts/Tn is 2.2 to 2.3 at 2 and 4 poles and 2.0 at 6 poles; this margin helps a loaded conveyor break away.
To select protective devices for these values you can use the overload, fuse and contactor selection page. The connection should be made by a qualified electrician.
Checklist before ordering a motor for a gearbox
- Does the gearbox nameplate show the IEC input size (e.g. 100 / 132) and the flange type (large B5 flange or small B14 flange)?
- Is the input bore 24, 28 or 38 mm; is the key width 8 or 10 mm?
- Is the input bore deep enough for the motor shaft length (50, 60 or 80 mm)?
- What is the highest input speed the gearbox maker allows?
- Have the required output speed, ratio (i) and motor poles been calculated together?
- Does the motor end up vertical in the gearbox mounting position? State this when ordering.
- Has the housing material (aluminium / cast iron) been chosen for the ambient conditions?
Since the catalogue has no dimension table for small B14 flange gearboxes, we give no figures here; confirm the flange size with us using the technical drawings. For the general selection of geared motors, read our geared motor selection guide.
Technical features that play a role in the price of a 3 kW flange motor
At this power, frame size (132S at 6 poles), housing material, compact or standard frame and mounting (B5 / B35) are decisive. The current figure for each model is shown on its own product page; to compare all options, browse the 120 models in our online store.
Motors at this power
- DRG-100L-2 – 3 kW – 2895 rpm – 100L: aluminium · cast iron
- DRG-100L2-4 – 3 kW – 1450 rpm – 100L: aluminium · cast iron
- DRG-132S-6 – 3 kW – 968 rpm – 132S: aluminium · cast iron
- DRG-90L-2K – 3 kW – 2895 rpm – 90L (compact, cast iron)
Click to see current prices and order these motors nowSEE PRICES →
Frequently Asked Questions
What is the shaft diameter of a 3 kW motor?
28 mm on 2- and 4-pole 3 kW motors (100L frame), 38 mm on the 6-pole (132S frame) and 24 mm on the compact DRG-90L-2K. For other powers see our motor shaft diameter by kW table.
What speed does a 3 kW 1500 rpm motor give through a gearbox?
The rated speed of DRG-100L2-4 is 1450 rpm; output speed is 1450 / i, for example 72.5 rpm at i = 20.
How many amps does a 3 kW motor draw?
At 380 V, DRG-100L-2 draws 6.02 A, DRG-100L2-4 6.34 A and DRG-132S-6 7.2 A.
How many kW is a 4 HP gear motor?
A motor sold as 4 HP is 3 kW.
Send us a photo of your gearbox nameplate and its input size and we will identify the matching 3 kW motor together: +90 (542) 666 11 11 · [email protected] · contact.
