Match switching, overload and control ratings separately
A motor starter combines switching and overload functions. Select it using the motor nameplate and the exact manufacturer's ratings: voltage, phase, load duty, full-load current, overload range and control-coil supply. Eaton's starter selection explanation identifies nameplate data and operating requirements as selection inputs.
Worked screening example: Eaton A27CGD25A024
Synthetic motor inputs compared with a real product data sheet; this is a screening example. Assume a three-phase, non-reversing motor with nameplate current 20 A and a 120 V AC, 60 Hz control supply. The manufacturer's A27CGD25A024 specification lists 25 A inductive full-load rating, a 16–24 FLA overload range, a 110–120 V 50/60 Hz coil, three-phase operation and a NEMA Type 1 enclosure.
| Check | Comparison | Screening result |
|---|---|---|
| Operating current | 20 A ≤ 25 A IFL | Within the stated current rating; verify voltage and duty rating too |
| Overload range | 16 A ≤ 20 A ≤ 24 A | Nameplate current lies inside the adjustment range |
| Control supply | 120 V, 60 Hz against 110–120 V, 50/60 Hz | Matches the stated coil supply |
| Starting function | Non-reversing three-phase | Matches the assumed function |
| Enclosure | NEMA Type 1 | Check the actual location and environmental requirements |
The screening result is candidate for further checking. Motor operating voltage, horsepower/duty rating at that voltage, starting frequency, available fault current and coordinated protection are still needed. If the synthetic nameplate current changes to 26 A, it exceeds both the listed 25 A IFL rating and the 24 A overload-range maximum; this model fails this screen. If only the control supply changes to 24 V, the listed coil also fails the screen. The model suffix is not a reliable substitute for reading the specification.
Choose and set overload protection
An overload range is the current interval the relay can cover. It is not an instruction to set its dial at 125% of nameplate current. Use the specific relay's adjustment procedure, motor nameplate/service-factor information, trip class and applicable motor rules. Keep overload protection separate from short-circuit and ground-fault protection; neither the contactor's current rating nor the coil voltage determines a fuse or breaker size.
NEMA, IEC and the final selection record
NEMA size and IEC utilization category are different selection systems. Compare the exact rated duty and voltage rather than converting labels using a universal horsepower chart. For U.S. installations verify the locally adopted NFPA 70 edition, equipment listing and manufacturer coordination data. In Japan, use the applicable Japanese installation rules and local manufacturer specifications; NEC or NEMA terminology alone does not establish local compliance.
- Save the motor nameplate, operating voltage/phase, starting method and starts per hour.
- Record the selected model, switching rating at operating voltage, overload model/range/settings and control supply.
- Confirm enclosure, short-circuit current rating, protective-device combination, wiring, disconnect and interlocks before purchasing.
Estimate motor current when preparing a preliminary worksheet; an estimate cannot replace the nameplate value required for overload selection.