How to Read an Industrial Motor Nameplate

Manufacturer and type/model: identify the unit and help locate the correct technical data. kW: usually rated mechanical shaft output, not electrical power drawn from the mains. V and A: rated line voltage and the associated full-load line current. They must be read as a matched pair.

cosφ / PF: rated power factor, used with real input power calculations where measured kW is unavailable. rpm: rated speed, usually below synchronous speed on induction motors due to slip. Hz: supply frequency for that row.

IE class (IE1–IE4): the motor efficiency class under relevant test and rating conditions; it is not itself an efficiency percentage. Efficiency η: where supplied, the rated output/input power ratio. IP rating: enclosure protection against solids and water. Frame, duty and insulation: useful for replacement selection, installation and operating limits.

A dual-voltage three-phase plate can display 230/400 V Δ/Y or 400/690 V Δ/Y. The delta (Δ) rating uses the lower listed line voltage; star (Y) the higher. The motor must be connected for its supply and nameplate rating.

For 400/690 V Δ/Y, 16.7/9.65 A, normal running on a 400 V three-phase supply is 400 V delta at 16.7 A. The 9.65 A figure applies to 690 V star. By contrast, a 230/400 V Δ/Y motor normally runs in star at 400 V. A star–delta starter may temporarily use star during starting, but the normal running connection must match the equipment design.

Some plates have separate rows for 50 Hz and 60 Hz. They can give different speed, voltage, current, rated output, efficiency or PF. Identify the actual supply and use values from the same frequency and connection row; do not mix a 50 Hz current with a 60 Hz kW rating.

An illustrative four-pole motor has two rated connections: 400 V Δ at 16.7 A and 690 V Y at 9.65 A, 50 Hz. For a verified 400 V delta-running installation, record 400 V and 16.7 A. Record the rated kW, PF, efficiency and speed from the same 50 Hz rating.

Do not use the 9.65 A 690 V star value to estimate loading on a 400 V delta connection: doing so makes the motor appear far more heavily loaded than it is.

Clean the plate when safe, photograph it square-on, and capture a second image if glare or dirt obscures a digit. Engraved dark plates, rotated plates and multiple rating rows are common extraction pitfalls. Check the proposed voltage, connection and corresponding current before saving.

MotorForge can pre-fill fields to reduce typing; it is not a substitute for a competent person checking the plate. For load estimates, see how to estimate motor load from measured current.