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46 VAV-PRC011M-EN
Single-Duct VAV Terminal Units
Minimum Circuit Ampacity (MCA) Equation
MCA = heater amps x 1.25
Maximum Over Current Protection (MOP) Equation
MOP = heater amps
However since MOP is less than or equal to MCA, then choose next fuse greater than MCA.
Units without electric reheat would use smallest fuse sizing.
Standard Fuse Sizes: 15, 20, 25, 30, 35, 40, 45, 50, and 60.
Example–For MOP of Single-Duct Unit
A model VCEF, electric reheat unit size 14 has 480/3 phase 15 kW electric reheat with 2 stages.
15 kW – 480/3 heater
15x1000/480x1.73=18.06
MCA = 18.06 x 1.25 = 22.58 amps. Since MOP is less than or equal to MCA, then MOP = 25.
Useful Formulas
kW = 1214 X L/s X ATD
ATD = kW / 1214 X L/s
kW
Cfm ATD×
3145
--------------------------------
=
3φamps
kW 1000×
PrimaryVoltage 3×
------------------------------------------------------------------
=
ATD
kW 3145×
Cfm
-------------------------------
=
1φamps
kW 1000×
PrimaryVoltage
--------------------------------------------------- -
=
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