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30
CAB-PRC001-EN
Minimum Circuit Ampacity
(MCA) and Maximum Fuse
Size (MFS) Calculations
Units with Electric Heat
HACR (heating, air conditioning, and
refrigeration) type circuit breakers are
required in the branch circuit wiring for all
units with electric heat. To compute MCA
and MFS, see Tables ED-2 through ED-5
on page 31 for motor FLAs and Tables
ED-6 through ED-8 on pages 32-33 for
electric heat amps.
Calculating electric heat amps:
Single stage, three phase =
heat kW * 1000/1.732/volts
Two stage, three phase =
total heat kW * 1000/1.732/volts
Note: Use 240V heat voltage for 230V
units.
Calculating MCA:
MCA = 1.25 * (heat amps + sum of all
motor FLAs)
Calculating MFS:
MFS = (2.25 * largest motor FLA) +
second motor FLA, size 10-12 units only +
heat amps
Use the closest larger fuse or HACR
circuit breaker above the MCA. Standard
fuse sizes are: 15, 20, 25, 30, 35, 40, 45,
50, 60 amps.
Electric heat MBH = heater kW * 3.413
Units Without Electric Heat
To compute MCA and MFS, see Tables
ED-2 through ED-5 on page 31 for motor
FLAs and Tables ED-6 through ED-8 on
pages 32-33 for electric heat amps.
Calculating MCA:
MCA = (1.25) x largest motor FLA +
second motor FLA, unit sizes 10-12 only
Calculating MFS:
MFS or HACR
1
type circuit breaker = 15
amps for all units without electric heat.
1
HACR (heating, air-conditioning and
refrigeration) type circuit breakers are
required in the branch circuit wiring for
all size 10 and 12 units.
Table ED-1. Decimal to Fractional HP (kW)
Conversion
Unit Size Decimal Fraction
02 .03
1
/
30
.07
1
/
15
03 .04
1
/
25
.05
1
/
20
.08
1
/
12
04 .05
1
/
20
.06
1
/
16
.10
1
/
10
.13
1
/
8
06 .07
1
/
15
.12
1
/
8
.16
1
/
6
.24
1
/
4
08 .12
1
/
8
.13
1
/
8
.24
1
/
4
10 .05 .07
1
/
20
1
/
15
.06 .12
1
/
16
1
/
8
.10 .16
1
/
10
1
/
6
.13 .24
1
/
8
1
/
4
12 .05 .12
1
/
20
1
/
8
.06 .13
1
/
16
1
/
8
.10 .24
1
/
10
1
/
4
.13 .24
1
/
8
1
/
4
Note:
Values for fractional HPs (kWs) are approximate values and
not necessarily the actual HP (kW).