HVAC Electrical Submittals: Coordinate kW, kVA, MCA and MOCP Correctly
Coordinate an HVAC electrical submittal using the selected equipment’s electrical supply requirements, its actual input-power basis and the manufacturer’s circuit ratings. Keep cooling capacity, motor shaft output, electrical input, apparent power and protective-device ratings in separate fields. A correct current calculation is useful for checking consistency, but it cannot replace the equipment’s approved electrical data or the electrical design.
The worked example below is illustrative and does not select a cable, fuse, breaker or disconnect. Final design and installation require qualified electrical professionals using the applicable local rules, current equipment instructions and actual site conditions.
1. Ask what each kW figure represents
A cooling unit might show 105 kW of thermal cooling capacity and 32.4 kW of electrical input at a stated duty. Those figures describe different energy flows. A fan schedule might also list a motor’s rated shaft output, which does not include the motor’s conversion losses or an upstream drive’s losses. Identify the measurement boundary before transferring a number into a load schedule.
Schneider Electric’s Altivar power explanation distinguishes motor-shaft power from electrical power. For coordination, request a supplier statement covering the complete selected unit at the specified duty and supply. Clarify whether compressors, fans, pumps, electric heaters, controls and accessories are included and whether any require separate supplies.
Thermal capacity, kW: the heating or cooling duty delivered under stated conditions.
Motor output, kW: mechanical power available at the shaft on the stated rating basis.
Electrical real input, kW: power taken across the specified electrical boundary.
Electrical apparent power, kVA: the voltage-current loading used with power factor to relate supply current and real input.
Do not calculate electrical connected load from thermal capacity alone. Equally, do not add a separate fan input to a supplier’s whole-unit input unless the supplier confirms that the fan is excluded. A clear inclusion list prevents both omissions and double counting.
2. Record voltage, phase and power-factor basis
For a balanced three-phase supply, using line-to-line voltage V and line current I, apparent power is S = √3 × V × I ÷ 1000 in kVA. Real input is P = S × PF in kW. Therefore I = 1000 × P ÷ (√3 × V × PF). Schneider Electric’s three-phase kVA guidance provides the underlying voltage-current and kW-to-kVA relationships.
Use line-to-line voltage in this form of the equation. A single-phase circuit uses a different relationship. Also identify whether power factor means true PF or displacement PF. Schneider Electric’s power-factor documentation explains that true PF includes harmonic content while displacement PF considers the fundamental frequency. This distinction matters when reviewing variable-speed drives and other nonlinear loads.
Request the relevant input-current data from the equipment or drive manufacturer. A motor’s output-side power factor should not be assumed to describe the supply side of its drive. Keep voltage, frequency, phase count and neutral requirement together in the equipment schedule so that a supply mismatch remains visible.
3. Worked three-phase consistency check
Consider a hypothetical packaged unit with a verified whole-unit real input of 32.4 kW at one specified operating point. Assume a balanced 400 V line-to-line, three-phase supply and a true input power factor of 0.90 at that same point. The 105 kW cooling capacity is recorded separately and is not used in this electrical calculation.
Apparent input: S = 32.4 ÷ 0.90 = 36.0 kVA.
Line current: I = 36.0 × 1000 ÷ (√3 × 400) = 51.96 A, approximately 52.0 A.
Reverse check: √3 × 400 × 51.96 × 0.90 ÷ 1000 = 32.4 kW.
If PF were incorrectly assumed to be 1.00, the calculated current would be 46.8 A, about 10% below the stated example’s current. That discrepancy is a reason to clarify the input data, not an instruction to increase a protective-device rating. The operating-point current is also not automatically a maximum current, startup current or minimum circuit ampacity.
If a supplier table lists a materially different current, compare the duty, voltage, operating mode and included loads before declaring an error. Rated, maximum and selection-point values may legitimately differ. Document the explanation so the mechanical schedule and electrical load list refer to the same equipment configuration.
Original balanced three-phase illustration at one assumed operating point. The calculated 52 A is not a cable or protective-device selection.
4. Read MCA and MOCP as circuit coordination data
Where these markings apply, MCA means minimum circuit ampacity: a minimum supply-conductor ampacity requirement for the identified circuit. MOCP means maximum overcurrent protection: the maximum permitted protective-device rating under the equipment’s stated conditions. The allowed device type also matters. A maximum-fuse marking should not be casually changed into a breaker selection.
UL’s Electrical Heating and Cooling Equipment Marking and Application Guide explains these markings, supply-circuit boundaries and their relationship to unit ratings. It is explanatory background, not a substitute for the current adopted code or instructions for the selected product. These labels are especially familiar in North American equipment documentation; other markets may use different terminology and design procedures.
Do not treat MCA as measured running current or MOCP as the current the unit normally draws. Likewise, MCA alone is not a breaker setting, and MOCP alone does not determine conductor size. Motor overload protection, branch-circuit protection, conductor sizing and equipment ratings have related but distinct responsibilities that the electrical designer must reconcile.
5. Make the submittal review actionable
Match the equipment tag and full model code to the latest mechanical selection, including motor, heater, pump and accessory options.
Identify every incoming supply and which internal or remote loads it serves; mark separately fed accessories explicitly.
Obtain rated or maximum input data on the manufacturer’s stated basis, operating-point input, startup information, phase, voltage, frequency and PF where relevant.
Record MCA, MOCP or equivalent requirements exactly as provided, including protective-device type, terminal limitations and relevant document revision.
Have the electrical designer check installation method, ambient temperature, grouping, conductor and terminal ratings, voltage drop, fault level, protective coordination and disconnect requirements.
Resolve discrepancies through a documented supplier response, then update the affected schedules and drawings together.
A practical review comment is specific: “Confirm whether the quoted 32.4 kW includes the supply fan and controls, identify separate heater supplies, and provide circuit ratings for the selected 400 V configuration.” It gives the supplier a question that can be answered and gives the electrical team a defined hold point.
Close the equipment-to-panel information loop
At delivery, reconcile the installed nameplate, accepted submittal and panel schedule before energization. Record approved substitutions rather than relying on a catalogue family name. A later motor or heater change can invalidate an earlier coordination check. Retain the accepted electrical data beside the equipment record so maintenance teams can identify the basis of the installation.
For related review habits, see like-for-like MEP supplier quotations and HVAC maintenance handover baseline readings.
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