In a sprinkler system, what is the function of the valve known as the backflow preventer or clapper?
A. It prevents water from entering the system.
B. It prevents water from the system from reentering the public water supply.
C. It prevents water from entering noninvolved areas.
D. It protects the system from water surges.
Answer: B. It prevents water from the system from reentering the public water supply.
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Which of these conditions will cause the flame to lift off the burner surface?
a. Too much primary air b. Too little primary air c. Too much secondary air d. Too little secondary air
A 15 hp, 209 V, three-phase, six-pole, Y-connected induction motor has the following parameter values per phase:
The motor slip at full load is 3%, and the efficiency is 90%.
a. Calculate the starting current. (Ignore the magnetizing current.)
b. Determine the starting torque.
c. Determine the maximum torque.
d. Calculate the value of the resistance that should be added to the rotor circuit
to reduce the starting current by 50%.
e. What is the starting torque in part (d)?
f. Calculate the value of the resistance that should be added to the rotor circuit
to increase the starting torque to maximum.
g. What is the starting current in part (f)?
Kilowatt-hour meters are used to measure __________.
a. electrical power b. electrical energy c. large amounts of voltage d. large amounts of amperage
The terminal and wire resistance values are critical in electric furnaces because the large current draw from the strip heaters
A) causes electro radiation B) causes arcing to ground at connections with a high resistance C) turns even small resistances into heat that accelerates oxidation D) increases if the overall circuit resistance increases