When renewing a WAT electric motor that is flange-mounted to a gearbox input, what matters is how the motor seats on the gearbox input flange and shaft bore. Since the gearbox stays, the new motor has to fit this connection. This article explains which dimensions to take on the gearbox side, how to read the flange type of the WAT motor and what information an assessment with DRG MOTOR needs.

Grey three-phase electric motor with DRG MOTOR logo – flange and shaft checks for a motor mounted on a gearbox input

Clarifying the scope: the motor is replaced, not the gearbox

This article is not about a gearbox product but about a standard WAT electric motor flange-mounted to a gearbox. This assessment covers the selection of the electric motor to be connected to the existing equipment. If the gearbox itself shows wear, oil leaks or gear damage, that must be examined separately by a technical team familiar with the gearbox.

Also check whether your motor has a brake. The WAT catalogue lists brake motors as a separate family; on hoists, inclined conveyors or drives that must hold position, the motor at the gearbox input is often a brake motor. Fitting a standard motor without a brake in place of a WAT brake motor can remove the machine's stopping and load-holding function, so such a replacement must always be assessed separately. If your motor has a brake, a separate fan or a drive integrated into the motor, state this too; these features change the assessment.

Dimensions that define the gearbox input connection

In the WAT type code, FA indicates B5 (large flange) and FB or FC B14 (small flange). Both are used on gearbox inputs. Before replacement, gather:

  • Flange type: a large flange with through holes (B5) or a small flange with tapped holes (B14)?
  • Flange dimensions: outside diameter, spigot diameter, pitch circle, hole diameter and number of holes.
  • Shaft: diameter × length and key width. The gearbox input bore (hollow input shaft or coupling hub) is machined to this size.
  • Gearbox nameplate: input speed, ratio and recommended motor power are on the gearbox plate; note them too.

Even when flange type and dimensions match, a shaft a few millimetres shorter may leave the key without full engagement in the input bore. The same kW and the same 1500 rpm class are not enough to keep the output speed either: gearbox output speed results from the motor's nameplate speed and the ratio together. Two 4-pole motors with rated speeds of 1420 rpm and 1460 rpm, for example, give slightly different output speeds on the same gearbox.

B5 and B14 on the DRG side

The DRG catalogue gives B5 large-flange dimensions by frame, and this table is the basis of the assessment. DRG also offers a B14 small-flange option, but since B14 dimensions are not in our catalogue they are confirmed separately at order. If your WAT motor is coded FB or FC, measuring the flange directly on the motor or gearbox input and sending the values is particularly important. DRG drawings are on the technical drawings page.

Send DRG MOTOR photos of the gearbox and motor nameplates with the flange and shaft values you measured, so the match between motor and gearbox input can be assessed on technical data.

DRG models with B5 flange that can be assessed

DRG Motor is a manufacturer, supplier and seller of electric motors. For gearbox inputs, the following models in the DRG shop and their B5 values (P/N/M/S, mm) can be reviewed:

  • DRG-802-4 – 0.75 kW, 4 poles, frame 80, rated speed 1420 rpm; B5 200/130/165/12, shaft 19×40 mm, key 6 mm.
  • DRG-100L1-4 – 2.2 kW, 4 poles, frame 100L, rated speed 1450 rpm; B5 250/180/215/14.5, shaft 28×60 mm, key 8 mm.
  • DRG-132M-4 – 7.5 kW, 4 poles, frame 132M, rated speed 1460 rpm; B5 300/230/265/14.5, shaft 38×80 mm, key 10 mm.

Further information for gearbox applications is on the electric motors for gearboxes page.

Frequently asked questions

My gearbox input flange is B14; can a DRG motor be fitted?

DRG offers a B14 option, but its dimensions are confirmed at order. Nothing can be said about suitability until the flange and shaft dimensions taken from the gearbox input are provided.

My current motor has a brake; can I use one without?

If the brake holds the load or provides a safe stop, a motor without a brake does not fulfil that function. This must be assessed separately with regard to machine safety; send the brake details (type, voltage, braking torque) with the nameplate data.

How is the motor chosen if the gearbox is also replaced?

This assessment covers the selection of the electric motor to be connected to the existing equipment. If the gearbox is also replaced, the motor must be compared against the new gearbox's input flange, shaft bore and recommended motor power.

Will the gearbox output speed change?

If the new motor's rated speed differs from the old one, output speed changes in the same proportion. Whether the difference matters depends on the application.

Information to send to DRG MOTOR

  • Photo of the WAT motor nameplate and full type code (FA/FB/FC letters, brake information)
  • Gearbox nameplate: input speed, ratio, recommended motor power
  • Flange dimensions: outside diameter, spigot diameter, pitch circle, hole diameter/number or thread size
  • Shaft diameter × length and key width
  • Mounting position (horizontal, vertical) and machine type (conveyor, mixer, hoist, etc.)
  • Start frequency and whether starting is under load

Send the information via WhatsApp, build a quote list, call +90 (542) 666 11 11 or write to info@drgmotor.com. The option is assessed by setting the gearbox input and motor dimensions side by side. Contact

See current prices of DRG MOTOR electric motors and order online in our storeSEE PRICES →

Technical Sources

  • WAT Motor Sanayi ve Ticaret A.Ş. — Ürün Kataloğu (Product Catalogue, Turkish edition) — IM tr 24.0 — Motor type codes (Motor Tip Kodları) — printed page 16 (PDF page 18).
  • WAT Motor Sanayi ve Ticaret A.Ş. — Ürün Kataloğu (Product Catalogue, Turkish edition) — IM tr 24.0 — Mounting arrangements, including the locating bearing note (Yapı Şekilleri) — printed page 12 (PDF page 14).
  • WAT Motor Sanayi ve Ticaret A.Ş. — Ürün Kataloğu (Product Catalogue, Turkish edition) — IM tr 24.0 — IE3 three-phase aluminium motors, dimensions B5, B35 — printed pages 47–49 (PDF pages 49–51).
  • WAT Motor Sanayi ve Ticaret A.Ş. — Ürün Kataloğu (Product Catalogue, Turkish edition) — IM tr 24.0 — Brake motors, technical information (Frenli Motorlar) — printed page 100 (PDF page 102).