How to Read a Motor Nameplate

May 17, 2026

Practical skill #1: what does 400V / 50Hz / 18.5kW / IP55 / S1 / FLC 34A / Ins. Class F actually mean? Every number on a motor nameplate explained in plain language.

DATE: 2026-05-17

Every motor has a metal plate riveted to its frame. It looks cryptic. But once you can read it, you can replace, spec, and troubleshoot motors without guessing.

Example nameplate: Siemens 1LE1001 | IM B3 | 50/60Hz. kW: 18.5/22 | V: 400Δ/690Y | A: 34.0/19.6. RPM: 1475/1770 | IP55 | Ins. Cl. F | S1 | cosφ: 0.86

Section 1: The Basics

Type/Model: manufacturer's model number — for spare parts or datasheet lookup.
IM Code (Mounting): B3 = foot-mounted. B5 = flange. B35 = foot + flange.
Frequency: 50Hz (Europe) or 60Hz (Americas). Speed is proportional to frequency.

Section 2: Power and Electrical

kW (Rated Power): mechanical power delivered to the shaft. NOT the electrical power consumed.
Voltage (V): 400Δ/690Y means in Delta connect to 400V, in Star connect to 690V.
Current (A): Full Load Amps — use THIS to size cables, contactors, and VFDs, not the kW!

Section 3: Speed and Performance

RPM: rated speed at full load. 1475 rpm = ~1.7% slip below synchronous 1500 rpm — normal.
cosφ (Power Factor): 0.86 = 86% of current does useful work. Low PF = utility penalties.

Section 4: Protection and Environment

IP Code: IP55 = dust-protected + water jets. IP23 = indoor only. IP66 = hose-down. IP68 = submersible.
Insulation Class: F = 155°C (standard). H = 180°C (extreme). Higher = more heat tolerance.
Duty Cycle (S-code): S1 = continuous. S3 = intermittent.

Common Mistakes

Using kW to size cables: WRONG. Always use Full Load Amps.
Ignoring IP rating: IP23 outdoors = failure in weeks.
Forgetting ambient: nameplate assumes 40°C. Hotter = derating.

The One-Minute Summary

Check three things in order:

1. Voltage and winding (Δ/Y) — can your supply match it?
2. Full Load Amps — what size cable, contactor, overload relay?
3. IP and Insulation — suitable for the environment?

Those three checks prevent 90% of installation mistakes.

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