Relays and Contactors Flashcards
What are the four categories of electromagnetic relays?
plug in, industrial, power, low voltage
What are the two types of pins in plug in relays?
tubular, spade
How many terminals would be associated with one NO/NC contact on a plug in relay?
three
How many operating coils does a latching relay have?
one or two
How can we increase the number of contacts that an industrial control relay operates?
we can install adder decks
Which type of relay uses open-type exposed contacts?
power relay
A relay has two sets of ratings for voltage and current. One set is for the _____ and the other is for the _____
contacts, coils
What are the switching arrangements for Form C contacts?
SPDT
What are the switching arrangements for Form A contacts?
SDST-NO
What are the switching arrangements for Form X contacts?
SPST-NO-DM
A relay’s rating may be classified according to which two agencies?
NEMA, IEC
Are a contactor coil and its movable contacts physically linked?
no
they are electrical linked
When are a set of normally open contacts in the open position?
when the circuit is de-energized
What are the three main components of a contactor?
core, coil, armature
Why do we laminate the iron or steel armature?
to reduce eddy currents
What are installed to minimize chattering and its undesirable noise and heating effects?
shading coils
What is a cause of chattering contacts?
undesirable heating
What are the three different types of contact material?
copper, silver, cadmium
Why can’t silver be used for high current application?
too soft
Copper contacts are more prone to _____ and _____ than cadmium contacts
pitting, oxidization
What is the best material for contacts to be used for a wide variety of application?
cadmium
Why must relay contact springs provide the right tension?
to prevent contact bounce and provide good continuity
What does the wiping action of contacts provide?
self-cleaning and confines the arcs to the tip of the contacts
Incorrect spring tension can cause contacts to ______
overheat
Bridge contacts help reduce _____ _____
electrical arcing
How many places can bridge contacts open?
two
What are two advantages of bridge contacts?
good contact alignment and provide a wiping action
What is the seal in voltage?
the voltage at which the armature completes its full physical travel and the air gap in the magnetic circuit is closed
At what percentage (approx.) is drop out voltage?
50%
If material in a magnetic circuit changes from air to iron, the permeability of the core of the coil ____
increases
When inductance increases, impedance _____
increases
An increase in impedance causes the current to ____
drop
What is the maximum voltage that can be applied to a coil (percentage)?
110% of rated voltage
State three reasons for an armature to fail to drop out after it is de-energized
welded contacts, jammed armature, residual magnetism
Can a lower than rated voltage applied to a coil damage it?
yes
A low voltage condition causing contact chatter could result in ____ _____ developing at the contacts
resistance
