Motor Starters Flashcards
In general, NEMA contactors cover a broader range of horsepowers than IEC contactors, for one size.
Yes.
There are fewer sizes of NEMA contactors than IEC.
What is the range of maximum current for sizes 00 to 9 for a NEMA contactor?
9A (00) - 2250A (9).
What are auxiliary contacts used for in a contactor?
Pilot duty.
What are the three types of starters?
Full voltage,
Reduced voltage (reduce the inrush current),
Reversing.
Which CEC table should be referenced when selecting an enclosure for a motor starter?
Table 65.
What factors affect the temperature rise of a motor?
Magnitude of load current, Duration of the overload, How frequently it starts, Time taken to start, Ambient temperature, Cooling ability of the motor, Motor's duty cycle.
What is single phasing of a motor?
How can this occur?
The loss of one phase in a three phase circuit.
Loose connection,
Break in on supply conductor or motor winding,
Blown fuse (if not supplying ctrl cct),
Burnt out contact,
Burnt out overload heater.
If a motor is running and becomes single phased, how does the current in the other two phases change?
It increases to more than 173% of normal current. Motor may stall if carrying more than 35% of it’s rated load.
When referring to overload devices, what is “trip class”?
The speed at which the overload trips.
10 being the fastest, 30 being the slowest.
Which overload heater does not provide an ambient temperature compensation?
Solder pot.
How do electromagnetic overload relays compensate for time delay?
Through use of a dashpot filled with liquid or gas under pressure.
When a critical industrial process is involved, which type of overload relay should be used?
A fully adjustable/programmable microprocessor controlled relay.
