For your next shop project you are going to build and gain an understanding of the circuit in figure 24. This circuit consists of a 120V power source, a MARS relay with a 24 Volt Coil, two 120 Volt light bulbs and a switch.
1. Look at the circuit in figure 24 without wiring it and use the space below to describe the sequence of operation. Write down what happens when you plug the circuit in. Then separately write down what happens when you turn the switch on.
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Switch On:
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Figure 24 – Transformer and relay shop circuit
2. Use your trainer board and make sure you have correctly identified the 24 volt coil relay. Wire the circuit shown in figure 24. Make sure you use different color wires for the low voltage (control) side of the circuit. Use Black and White for the line side and use Orange and Yellow for the control side.
3. When wired have your instructor check the circuit and make sure that you do not have any shorts or safety issues. Have your instructor initial this step.
4. Plug the circuit in and turn it on. Use your meter with both the switch open and closed to fully understand what is happening with the voltage levels and the step downs and switches and loads.
5. Find the voltages between the points in the table below and record them. There are two steps, one with the switch open, and one with the switch closed.
| POINT 1 | POINT 2 | VOLTAGE |
| 1 | 6 | |
| 1 | 2 | |
| 1 | 3 | |
| 1 | 4 | |
| 1 | 5 | |
| 1 | 8 | |
| 1 | 7 | |
| 10 | 9 | |
| 10 | 12 | |
| 10 | 11 | |
| 10 | 13 | |
| 9 | 12 | |
| 9 | 13 | |
| 9 | 11 | |
| 6 | 2 | |
| 9 | 3 |
6. Now close Switch 1 and record the voltages.
| POINT 1 | POINT 2 | VOLTAGE |
| 1 | 6 | |
| 1 | 2 | |
| 1 | 3 | |
| 1 | 4 | |
| 1 | 5 | |
| 1 | 8 | |
| 1 | 7 | |
| 10 | 9 | |
| 10 | 12 | |
| 10 | 11 | |
| 10 | 13 | |
| 9 | 12 | |
| 9 | 13 | |
| 9 | 11 | |
| 6 | 2 | |
| 9 | 3 |
7. Does the actual sequence of operation match the one you wrote down in step 1 of the shop exercise?
8. Before you take the wire off your panel make sure you have your instructor check your work and then sign off on this shop assignment.
9. Make sure you are able to identify the voltages you should have without using a meter. If you are a student in a classroom this skill will be on every test until you graduate. In order to fix something that is broken you must know how it is supposed to work when it is running properly.