HVAC ELECTRICAL CONCEPTS TEST
QUESTIONS AND ANSWERS
What are the analogies comparing electricity in a wire to water in a pipe? -
ANSWER Current = flow, voltage = pressure, resistance = friction
T/F: All power supplied is delivered with A/C current. - ANSWER False,
some is lost. Total useful power = REal Power = P = IV * Pf where Pf is power
factor (0.85 for single phase).
This is more theoretical then practical for a plug and chug problem.
Mechanical Horsepower - ANSWER Amount of power required to meet the
needs of the system. MHP. Discharge of fan or pump.
Pump/Fan Horsepower - ANSWER Brake Horsepower BHP = MHP / pump
efficiency. Power into pump/fan required to perform work.
T/F: Standard Horsepower is usually higher than BHP - ANSWER True.
Standard Horsepower comes in standard increments that typically exceed the
required Pump/Fan BHP.
Electrical Power Input (related to Horsepower) - ANSWER Motor HP
(standard) / Motor Efficiency
Electrical Power Supplied (Apparent Power) - ANSWER Electrical Power
Input / Pf (power factor). Accounts for loss in power not in phase.
What is the general trend for the enclosure performance as NEMA type
increases? - ANSWER General Indoor -> Drip/Dust/Rain tight -> outdoor use
-> Corrosion resistant -> hazardous
QUESTIONS AND ANSWERS
What are the analogies comparing electricity in a wire to water in a pipe? -
ANSWER Current = flow, voltage = pressure, resistance = friction
T/F: All power supplied is delivered with A/C current. - ANSWER False,
some is lost. Total useful power = REal Power = P = IV * Pf where Pf is power
factor (0.85 for single phase).
This is more theoretical then practical for a plug and chug problem.
Mechanical Horsepower - ANSWER Amount of power required to meet the
needs of the system. MHP. Discharge of fan or pump.
Pump/Fan Horsepower - ANSWER Brake Horsepower BHP = MHP / pump
efficiency. Power into pump/fan required to perform work.
T/F: Standard Horsepower is usually higher than BHP - ANSWER True.
Standard Horsepower comes in standard increments that typically exceed the
required Pump/Fan BHP.
Electrical Power Input (related to Horsepower) - ANSWER Motor HP
(standard) / Motor Efficiency
Electrical Power Supplied (Apparent Power) - ANSWER Electrical Power
Input / Pf (power factor). Accounts for loss in power not in phase.
What is the general trend for the enclosure performance as NEMA type
increases? - ANSWER General Indoor -> Drip/Dust/Rain tight -> outdoor use
-> Corrosion resistant -> hazardous
