Minimum Circuit Ampacity 36.14 The minimum circuit ampacity (MCA) required by Clause 36.3(h) shall be determined as follows. All concurrent load conditions are to be considered in the determinations, see Figure 36.1. Whichever load condition provides the highest value shall be used. a) For a motor group only, a load consisting of two or more motors, the rated current of the largest motor or branch circuit selection current, if marked, (see Clauses 36.11 and 36.12), multiplied by 125 per cent, added to the rated currents of all of the other motors. b) For a combination load, a load consisting of one or more motors, electric heaters, and any other loads, that incorporates one or more compressor motors, the rated current of the largest motor compressor or branch circuit selection current, if marked, (see Clauses 36.11 and 36.12), multiplied by 125 per cent, added to which shall be the value obtained by multiplying the rated current of the electric heaters by 125 per cent, and adding to that total the sum of the ratings of all other loads. c) For a combination load, a load consisting of one or more motors, electric heaters, and any other loads, not involving a hermetic refrigerant motor compressor, the sum of the rated currents multiplied by 125 per cent. Exception: The rated current of the heater load may be multiplied by 100 percent, rather than 125 per cent, provided that 1) the rated heater load at a field wiring terminal is 50 kW or more; 2) the minimum conductor size that may be field-connected to such terminal is still to be marked; and 3) the heater element circuits connected to the field wiring terminals are subdivided as specified in Clause 30.8 and are arranged to be controlled by one or more temperature-actuated devices to reduce the likelihood of continuous simultaneous operation of all of the element circuits. 82 CSA-C22.2 No. 236 ‚ UL 1995 September 29, 1995 Figure 36.1 – Minimum circuit ampacity calculation On equipment with multiple modes of operation, every mode shall be considered for each individual field wired hazardous voltage circuit. Whichever load condition provides the highest value shall be used for Clause 36.14, in the applicable circuit. (Clause 36.14(a)) MCA = (1.25× LOAD1) + LOAD2 (Clause 36.14(b)) MCA = (1.25 × LOAD1) + (1.25* × LOAD3) + LOAD2 + LOAD4 (Clause 36.14(c)) MCA = 1.25 × (LOAD1 + LOAD2 + LOAD4) + (1.25* × LOAD3) where MCA = Minimum circuit ampacity per Clause 36.14 LOAD1 = Current of largest motor or branch circuit selection current, if marked, (see Clauses 36.11 and 36.12) LOAD2 = Sum of currents of all motors not including largest motor LOAD3 = Current of electric resistance heater LOAD4 = Any other load rated 1.0 A or more *If exception in Clause 36.14 applies, use 1.0 instead of 1.25
