Sizes the branch-circuit conductors, overcurrent protection and disconnect for HVAC motor-compressor equipment \u2014 the NEC Article 440 hermetic-compressor-specific method (which differs from a standard motor's NEC Article 430 sizing) or the IEC general method \u2014 with advanced support for multi-motor combination equipment and VFD-fed motors.
Standards followed
NEC Article 440 (air-conditioning and refrigerating equipment)IEC 60364-5-52 / IEC 60947-4-1 general method
What it can do
- Single motor-compressor Minimum Circuit Ampacity (MCA), Maximum Overcurrent Protection (MOCP) and disconnect sizing from RLA (and optional LRA).
- IEC general-method design current from a configurable margin factor.
- Advanced: multi-motor combination-load equipment sizing (largest-motor-at-125% + sum-of-others method).
- Advanced: VFD-fed motor input-side and output-side minimum circuit ampacity, sized separately.
Example problem
A hermetic compressor has a nameplate RLA of 18A (no LRA given). Size its NEC Article 440 branch circuit.
- Minimum Circuit Ampacity (MCA) = 125% × RLA = 1.25 × 18 = 22.5A.
- Maximum Overcurrent Protection (MOCP), per NEC 440.22(A): 175% × RLA = 31.5A is a maximum, so it rounds down to 30A; if 30A will not start the compressor it may be increased up to 225% × RLA = 40.5A, i.e. 40A.
- Disconnect minimum ampacity = 115% × RLA = 20.7A.
MCA 22.5A, MOCP 30A (up to 40A if needed to start), disconnect 20.7A minimum.
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