TM 5-688
APPENDIX C
Derating Factors
C-1. Heating, ventilation, and air conditioning (HVAC).
a. 50 Hz. The output of directlycoupled, motordriven equipment must be derated to account for the reduction in
shaft speed to 5/6 the 60 Hz value. Otherwise, the mechanical coupling used between the motor and driven equip-
ment should be purchased to give the required rotating speed. HVAC controls that are frequency dependent must be
purchased in 50 Hz configurations.
b. Voltage. Derating for voltage is not an option.
C-2. Electrical distribution and protection for transformers.
b. Voltage. Derating for voltage is not recommended. Vendors can provide almost any needed input voltage rat-
ing. Consult vendor regarding derating possibility if derating is absolutely necessary.
C-3. Electrical distribution and protection for power factor capacitors.
a. 50 Hz. Derate kilovolt-amperes reactive (KVAR) rating by multiplying 60 Hz KVAR rating by 5/6 to yield 50 Hz
WAR rating.
b. Voltage. Derating for voltage is not recommended. Vendors can provide almost any needed voltage rating.
Consult vendor regarding derating possibility if derating is absolutely necessary.
C-4. Electrical distribution and protection for protection equipment.
a. 50 Hz. Different trip curves may be needed. Consult vendor for these curves.
b. Voltage. Derating for voltage should not be needed. Verify with vendor since special protection equipment may
need derating.
C-5. Other electrical distribution and protection.
Derating either cannot or should not be performed. Contact vendors to purchase appropriately rated equipment.
C-6. Safety and security equipment.
a. 50 Hz. Depends on type of power supply. Derating is either not necessary or not possible. Contract vendor to
purchase appropriately configured power supply.
b. Voltage. Derating far voltage is not recommended. Contact vendor to purchase appropriately configured power
supply, or use transformer to convert supply voltage level to power supply input level.
C-7. Communication equipment.
a. 50 Hz. Depends on type of power supply. Derating is either not necessary or not possible. Contact vendor to
purchase appropriately configured power supply.
b. Voltage. Derating for voltage is not recommended. Contact vendor to purchase appropriately configured power
supply, or use transformer to convert supply voltage level to power supply input level.
C-8. Incandescent lighting.
a. 50 Hz. No derating necessary. lncandescents are frequency insensitive.
b. Voltage. Not possible. Bulb life will suffer drastically. Contact vendor to purchase high voltage bulbs, or use trans-
former to convert supply voltage to lamp voltage.
C-1
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