Roy Peters' Electricity Unit
(Click on any of the photos to enlarge)
Residential Electricity is like playing bingo. All you need to know is the rules of the game.
Devices will only be good for about 4 to 6 groups.
Don’t screw devices onto boxes.
Don’t over tighten clamps. This will damage the cable and could cause a short.
Use very long lengths of wire so that the ends can be cut off and the wire used again.
You can get students that are very good or ahead of the class to build a cable demo board.
You can get students that are very good or ahead of the class to build a circuit demo board.
Use a GFI cord to check all circuits. Preferably with an in line fuse to protect against short circuits. I made my own. Try to keep the fuse easily accessible as you will most likely have to change it a few times. A 3 amp fuse is all that is needed.
Use a receptacle tester to check out the circuits.
Use a low wattage bulb for the units. I use a refrigerator bulb as it is compact, can take more abuse and is low wattage (less current draw).
A GFI demo board is a lot of fun although it only takes 5 minutes to demo. This board shows how a GFI works. Basically, the GFI monitors the current going out on the black wire and the current returning on the white wire. If there is a difference between the 2 currents; the breaker in the plug trips, saving the person from electrocution. The person still gets electrified.
Day 1
Lecture on residential electricity in particular the service entrance, meter and breaker panel.
Start building workstations.
Another possibility is to build walls using 2x4 studs and use these to wire up the circuits. Good time to do lecture and activity on 2x4 wall spacing etc. photo
Day 2
Today we learned how to connect a household receptacle (PDF). Some important points to remember: rubber under the clamp, 6 inches minimum of wire in the box, ground wire under the ground screw in box and then to the ground screw on the receptacle, white wire on silver screw, black wire on brass screw, in a clockwise direction (this is not code) see photo. Students that finish quickly can add a receptacle (PDF) to the circuit.
Make sure that the students have met all the requirements above. If not, redo. Don’t allow them to get away with doing it next time as they won’t do it and will waste their time while others are doing the activity. I make them wire in a CW direction as it pulls the wire under the screw. Also, if the students just do stuff to code, they would almost all get a level 4.
Do not show the students until the end of the unit that you can just strip the wire and push it into the holes in the back of the plug. This is too fast and leaves you with a bunch of devices with bits of wire sticking out of them. Personally, I always use the screws when I do electrical work.
The electrical code provides for a “lack of workmanship rule”. Basically, if the inspector finds that the work seems to be to code but is obviously poorly done, he can fail the installation based on poor work man ship.
Day 3
Simple light circuit (PDF) where the power goes first to the switch and then to the light. This circuit is not desirable because you have to go the switch box if you wish to wire another section on this circuit (need neutral or white wire). Most new homes have the basement lighting wired in this manner, where the light switch at the bottom of the stairs turns on all the lights. Then the owner taps off one of the lights to wire a plug for the freezer. The freezer turns on and off with the basement lights. The circuit for the freezer must come from the light switch box. The loop circuit is much better and preferred as you can tap off of any light box to continue a new circuit. Also, light boxes are easier to get to in the basement and top floor of a home.
Day 4
Most likely, you will not be finished all the above. Good time to do the wire chart (PDF) and use what is left of the class to finish off circuits.
Day 5
Review of the simple light circuit (PDF), where the power enters the switch box and then goes on to the light box.
Did the loop light circuit (PDF), where the power enters the light box and then goes to the switch box. This circuit allows us to tap off a power supply from the light box to power other circuits.
In the loop circuit, the power goes first to the light box and then to the switch. In order to still have a black wire going to the brass screw of the light base, we have to connect the white of the switch wire to the black of the incoming power using a wire nut or marette. Any white wire connected to a black wire automatically becomes black or hot.
When you look in a light box and see a white wire under a wire nut (marrette) with black wires, you immediately know that this white wire is in the cable that goes to the light switch (it’s corresponding black wire will be on the brass screw or black wire of the lamp base). A long time ago, electricians had to put black tape around white wires that had become hot. This is no longer done.
To install a wire nut,
Use proper sized wire nut. See info on box.
Strip about 5/8 of the wire on all conductors.
Hold conductors together and twist on wire nut.
Must twist in a CW direction until wires twist around themselves.
Pull on marette, should stay on.
To check, remove wire nut and wires should be tightly twisted around each other.
Day 6
Final day for electricity. We did the loop light circuit and added a receptacle to it that would remain on at all times.
More Days
Should you find that the students enjoy this unit, there are more circuits available to be wired in the circuit’s folder. A good group could do a 3way switching demo, where a light is controlled from 2 separate locations (top and bottom of stairs). This 3 way circuit has the power going to one of the switches first. This 3 way circuit has the power going to the light box first.
Assessment
I usually break this up over a few days as there are not enough boards or tools to do the whole class at once, as they each work alone. When everyone has done the practical test, I then do the written test with the entire class.
A practical test which involves wiring a circuit.
I give them the diagram of the circuit with connections, as I am evaluating their practical skills, not their knowledge of circuit development. Also, if they don’t have the completed circuit, the weaker students will not be able to do the practical test. This is the circuit I use.
A written test
With multiple choice questions.
With circuit that they can wire on paper using coloured pencils or by identifying the colour of the wires. I always use the same circuit as the one they wired for the practical test.
Practical test:
Use any of the circuits that are labelled with question at the end of their name.
Use this check list to evaluate the wiring.
Written test:
Check the test folder for this test that you can use or modify to your liking.