Motor Full Load Current Calculator & Contactor Selector
Free tool for engineers and technicians: calculate three-phase motor current at 400 V and get instant DOL contactor and overload relay recommendations per IEC 60947-4-1.
Calculated: I = P / (√3 × V × cosφ × η). Always verify against the motor nameplate — actual FLC varies by design.
Recommended DOL starter components
| Contactor (AC-3) | Schneider LC1D18 | Siemens 3RT2018 | Chint NC1-1810 |
| Overload relay | Schneider LRD21 (12–18 A) | ||
| Motor circuit breaker | GV2ME (set ≈ 14.2 A) | ||
Sizing per IEC 60947-4-1 AC-3 duty for direct-on-line starting at 400 V. For star-delta, heavy starting or high ambient (>50 °C), contact our engineers.
Request a quote for this starterFrequently asked questions
How is motor full-load current calculated?
For a three-phase motor: FLC = P / (√3 × V × cosφ × η), where P is rated power in watts, V is line voltage, cosφ is power factor and η is efficiency. A 7.5 kW motor at 400 V with cosφ 0.85 and η 0.9 draws about 14.2 A. Always confirm against the motor nameplate — actual values vary by design and manufacturer.
How do I choose a contactor for a motor?
Select a contactor whose AC-3 rating at 400 V meets or exceeds the motor full-load current, per IEC 60947-4-1. For an 11 kW / 21 A motor, a 25 A AC-3 contactor (Schneider LC1D25, Siemens 3RT2026 or Chint NC1-2510) is the standard choice for direct-on-line starting.
What should the overload relay be set to?
Set the thermal overload relay dial to the motor nameplate full-load current. Choose a relay whose adjustment range contains the FLC — for 14 A, a 12–18 A relay such as the Schneider LRD21 mounted directly under the contactor.
Razz Middle East supplies genuine contactors, overload relays and motor circuit breakers from Schneider Electric, Siemens, ABB and Chint across Saudi Arabia — with a 4-hour response on every RFQ. Request a quote