Relay Circuit Assignment - Job #2
Here are the tasks to complete for this assignment. You may want to print
this page. Check off each task when done. Then move on to the next task.
Definitions Before You Begin
Be sure you have an understanding of these terms before beginning this exercise. You may need to use a dictionary, a code book, a theory book, or even
ask other electricians you may know for help. This is part of the learning
activity. Begin now.
terminology
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definition
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lighting contactor
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timer
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photo cell
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timer motor
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continuous load
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contacts
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timer contacts
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circuit
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VDC
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Read This
As background, here are some details which will help you understand this
assignment. If you encounter words, terms, phrases or abbreviations which you do
not understand, then stop. Research the meaning before going on. This is very
important to your learning activity. The essence of any technical education
activity is comprehensive understanding of all topics which are encountered.
Background Information
A light sensor photo cell can be used to control a load without a relay. The
switch leg out of the photo cell feeds the load. As long as the photo dell
voltage and current rating can supply the load, the photo cell without a relay
is the proper component for the job.
But if there are several loads to be energized by a single photocell, then
the photocell is used to control a relay which in turn can turn on and off any
quantity and any size loads.
Further, as in this wiring diagram, when a time clock is added, the
photocell can turn on the load and the time clock can turn the load off. A
perfect application for this circuit is parking lot lighting. The lighting comes
on at dusk and can go off at any time set on the time clock.
Any number of circuits can be wired to come on and go off at exactly the
same time. A lighting contactor can have many circuits associated with it
depending on the number of poles.
SOURCE
Typically in industrial relay logic circuits, but not always, the operating
voltage for the switch contacts and relay coils will be 120 volts AC. Lower
voltage AC and even DC systems are sometimes built and documented according to
"ladder" diagrams:
So long as the switch contacts and relay coils are all adequately rated, it
really doesn't matter what level of voltage is chosen for the system to operate
with.
Note the number "1" on the wire between the switch and the lamp.
In the real world, that wire would be labeled with that number, using
heat-shrink or adhesive tags, wherever it was convenient to identify. Wires
leading to the switch would be labeled "L1" and
"1," respectively. Wires leading to the lamp would be labeled
"1" and "L2," respectively. These wire numbers
make assembly and maintenance very easy. Each conductor has its own unique wire
number for the control system that it's used in. Wire numbers do not change at
any junction or node, even if wire size, color, or length changes going into or
out of a connection point. Of course, it is preferable to maintain consistent
wire colors, but this is not always practical. What matters is that any one,
electrically continuous point in a control circuit possesses the same wire
number. Take this circuit section, for example, with wire #25 as a single,
electrically continuous point threading to many different devices:
Go to the Diagram of this Job
Click HERE to go to the diagram, lecture, and picture for this exercise. Follow
the instructions found there. Then return to this page with your back button.
Connect the Components
Use the material list on the diagrams page to have ready all the components you
will need to complete this exercise. Connect all required components based on
the diagram.
Check your Connections
With the diagram as a guide, verify that all the connections have been made
properly.
Apply Power To Test
Wear safety glasses when testing this circuit. Locate the overcurrent protective
device for the circuit you will use. If possible, connect to a GFCI protected
circuit for the added safety. Be sure you have a full understanding of this circuit before applying power.
Then when you test the circuit, there should be no problem with it working
properly. Make corrections to the wiring as needed so the circuit works
properly. Memorize these connections.
Sketch the diagram from Memory
A sure way to determine if you have internalized this circuit is to draw a
sketch of the diagram from memory. You may choose to use a straight edge. But
that is not necessary. When you have completed the sketch, check it against the
diagram which is given for accuracy. Electricians must have the ability to
remember circuit connections without reference. Here is your chance to
demonstrate what you have learned. If you are unable to sketch the ladder
diagram from memory, refer back to the given ladder diagram. Then try again.
Repeat this activity until you feel confident that you can sketch this specific
diagram without reference.
Reconnect From Memory
Now on to the real test. Reconnect this diagramed circuit from memory. This will
ultimately tell you if you understand this circuit or not.
Review Before Answering Questions
Go back to review definitions, the diagram, the picture, your notes, your sketch
and any other details which will help you as you move on to the questions about
this diagram.
Answer the Questions
When you are satisfied that you can draw a sketch of the diagram, and wire it
all from memory, it is time to go on to answer questions about the diagram.
Click HERE to go to the questions.
Check Your Answers
When you have completed the questions, go on to check your answers. If you have
any which are different than the given answers, try to determine the reason. Go
back to the diagram. Research the question. Ask other electricians you may know.
But do all it takes to understand the correct answer to each question.
Click HERE to go to the answers.
Go On
When you can answer all questions without error, and strongly feel you
understand all answers, it is time to go on to the next assignment.
Click HERE
to go on to the next assignment page.
If you would like to research any of these topics further, enter the search
term in this Google Search Box:
Use these Relay Circuit links to go to where you left off in
your online activities.
Job
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Assignment
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Diagram
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Lecture
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Picture
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Questions
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Answers
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