UL 1995 36.14 seems to be the US standard for determining equipment MCA:

Also, it looks like nameplate motor currents aren't always used to calculate MCA;

https://www.titus-hvac.com/softwares...ecalculate.pdf

*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.

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.

Also, it looks like nameplate motor currents aren't always used to calculate MCA;

https://www.titus-hvac.com/softwares...ecalculate.pdf

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