4 Flashcards
Pole
a number of completely isolated circuits a relay can switch at one time
throw
the number of closed contact positions per pole
break
the number of separate places on a contact that open or close an electric circuit
describe the operation of a NCTC contact
opens instantly when energized closes on timer when reenergized
_____ timers are more accurate than _____ timers because they have no moving parts in their timing circuit that might be affected by heat humidity or pressure.
solid state / dashpot
since a contact has no voltage drop, placing it in parallel with load would create a _____
short circuit
which of the following features is typically not present on a magnetic contractor, but is present on a motor starter.
overload relays
solenoids convert electrical energy directly into ______ motion
mechanical
REED
a fast operating, single pole, single throw switch with normally open contacts hermetically sealed in a glass envelope
A repeat cycle timer is activated, and the load is energized for 15 seconds, and then reenergized for 30 seconds, with the cycle repeating continuously until the timer is deactivated. This timer is programmed for _______ operation.
asymmetrical
a dode timer has a single normally open contact. If the timer is set for 15 second delay, which of the following scenarios describes when the contact will change state from open to closed in the timing sequence
instantaneously, when the timer is energized
which of the following types of timers does not have an instantaneous contact available, which will close immediately when energized, before the timer times out
DOE electronic timer
the surface that most starter contacts is made from is _________
silver cadmium alloy composite
list the 3 basic parts of an AC solenoid
frame (support)
coil
armature (plunger)
during the operation of a timer, when do the instantaneous contacts change state?
when the coil is energized
name the 3 major factors that led to the discontinuation of knife switches to control motors
1 exposed live parts
2 soft copper arcing led to failure
3 opening and closing speed was determined by the operator
what are 2 types of thermal overload relays
eutectic alloy
bi-metallic
the damage to a motor caused by an overload is proportional to what 2 factors?
amount of current
direction of overload
list 3 basic methods that timers use to control timing
synchronous
dashpot
solid state
what are the 4 types of timing functions that electronic timers are capable of
delay on
delay off
recycle
one-shot
what are 3 basic types of overload relays
magnetic
thermal
electronic
list 2 reasons timing circuits are used in motor control applications
1 - to enable process events that are started and stopped at different intervals
2 - to reduce the need for multiple machine operators
