Panel and Mechanical Connection Checks When Ordering a 30 kW Electric Motor

When ordering a 30 kW (40 HP) motor, the motor itself is often the item that causes the fewest problems. Problems appear after the motor arrives on site: the breaker and thermal relay in the panel were not selected for this current, the cable cross-section is insufficient, a single cable was run where a star-delta panel needs six ends, the coupling hub does not fit the shaft or the base does not suit the new frame. This article explains, in order, which checks to carry out on the electrical panel and the mechanical connection before ordering a 30 kW industrial motor, and who should prepare which information.

Basic values of the 30 kW models

At HEM Motor, 30 kW is offered with a cast iron frame at three speeds. Below are the rated current, which is the basis for the panel calculations, and the IEC frame, which is the basis for the mechanical side:

All three models have a 400/690 V (Δ/Y), 50 Hz supply, IP55 protection and class F insulation. The 1,500 and 3,000 rpm models share the same 200L frame; the 1,000 rpm model moves up one frame to 225M.

Panel side: questions for the electrician before ordering

Replacing a motor or adding one to a new line requires the panel components to match the new motor's values. The following checks should be carried out by the plant's electrical engineer; the aim here is to clarify which questions to ask.

Supply and connection

• Supply voltage: on a 400 V supply the motor is connected in delta (Δ). If the plant has 690 V distribution, a star (Y) connection applies. State the measured voltage in your order.
• Starting method: at 30 kW, many plants prefer star-delta, a soft starter or a frequency inverter instead of direct-on-line starting. Which one is used depends on transformer capacity, the condition of the line and the machine's starting load.
• Number of cables: with star-delta, the terminal links are removed and the six ends go separately to the panel. If the existing installation has a single three-core cable, a second cable must be planned.

Protective devices

• Thermal relay or motor protection breaker: the setting range must cover the new motor's rated current. In a star-delta arrangement, the thermal relay is often set to the phase current; your electrician will know this detail.
• Contactor and fuse: it must be confirmed that contactors and fuses suit the starting current and the utilisation category.
• Cable cross-section: rated current, cable length, installation method and voltage drop are calculated together. If the old motor was smaller, the existing cable may not be sufficient.

Details on how protective devices are selected are explained in the article on thermal relay and fuse selection.

If a drive will be used

According to the general information on our site, our three-phase series can be used with speed control by a drive. Two conditions must always be stated in the order: if the motor will run for long periods at low speed with full torque, an external fan may be needed; if the cable between the drive and the motor is long, a dv/dt or sine filter is considered. In a drive application, writing down the speed range and cable length at the ordering stage prevents later changes. For details, see the frequency inverter question.

Mechanical side: connection and layout check

The weight and torque of a 30 kW motor leave no tolerance for mechanical mistakes. Before ordering, clarify the following:

• Frame size: compare the IEC frame size on the old motor's nameplate with the new model's. Moving from 200L to 225M changes both the shaft height and the foot hole spacing.
• Mounting arrangement: whether it will be foot-mounted (B3), flange-mounted (B5) or foot-and-flange (B35). Mounting options are offered according to the frame and the flange size is confirmed with the order; a summary is in the mounting arrangements question.
• Connecting element: coupling, belt and pulley, or gearbox. The bore and keyway of the coupling or pulley hub must fit the new motor's shaft.
• Shaft end: in the 200L frame, the shaft end dimensions of the 2-pole and 4-pole models may differ. The same frame size does not mean the same shaft; read the row for your own model in the 2D technical drawings.
• Handling and lifting: check that the area where the motor will be lifted by its eyebolt and set in place is suitable, with access for a crane or forklift.

A connection outside standard IEC dimensions (special shaft, double-ended shaft, special flange, brake arrangement, etc.) cannot be met by a standard motor. In such a case a special motor is required; ask us by sending the old motor's nameplate and dimensions.

Pre-order checklist

Example: renewing the motor of a 30 kW shredder

The following sequence is a hypothetical example. Suppose the motor of a shredder at a recycling plant, driven via a belt by a 1,500 rpm, 30 kW motor, is to be renewed.

• Nameplate and frame: the old motor's nameplate shows 30 kW, a rated speed of about 1,475 rpm and a 200L frame. This points to the 200L-4 model.
• Panel: the old motor starts in star-delta. If the shredder is emptied at the end of the shift and starts unloaded, this method can be kept. If the machine has to start full, the method is reassessed with the electrical engineer.
• Mechanical: the pulley hub is compared with the diameter and key of the new shaft; the foot holes and slide rail holes are checked against the technical drawing. Since the frame stays the same, the base will most likely not change.
• Power: even if the machine seems to struggle, the power is not increased based on the machine's name. First the starting method, belt condition and blade maintenance are checked; the load is measured if necessary.

At the same plant, models such as the 200L1-2 (30 kW, 2 poles, 2,960 rpm, IEC 200L) for a direct-coupled high-speed fan, or the 225M-6 (30 kW, 6 poles, 980 rpm, IEC 225M) for a slow-turning drum, could be considered; panel and mechanical checks are carried out separately for each.

Send with your order

• Power and speed (30 kW; 1,000, 1,500 or 3,000 rpm)
• Supply voltage, starting method and, if a drive is used, the cable length
• Mounting arrangement and connecting element (coupling, pulley, gearbox)
• Application and ambient conditions
• For a replacement, a photo of the old motor's nameplate and, if needed, the shaft dimensions

You can see the 30 kW options and each model's current price on our buy electric motors shop page. Other heavy-duty models are listed on the cast iron frame models page. To check compatibility with your current motor, send us the nameplate details; for other questions, reach us through our contact page.