Introduction: How to Make Wire Identification/Loop Check Phones
Basic Theory information: The LC phones are used with two people testing, verifying and identifying individual wires in multi-conductor cables or where the two ends of the cable may be in different buildings or areas. Imagine a picture of two kids talking to each other through soup cans and a string in between them. These LC phone are those soup cans and they really work.
The method for making these LC phones is achievable as soon as you find the phones (finding the phones are the hardest part).
a)Rewire the phones to a wire connection drawing.
b)On one phone install a switch and a 9 volt battery
c)On both phones install test leads according to the drawing.
d)Once the leads of both phones are touching, communications between both phones become possible.
An example of how this is used: Two guys were installing speakers and speaker wires in the walls for their home theater system. The speaker wires were installed at four speaker locations and all were not identified prior to pulling them all to the amplifier. There are (4) 2-wire cables at the amplifier and you don’t know which is the front right, front left, the rear right or the rear left wires. One of the LC phones will clip on to the two wires at the left rear location while the other phone will be connecting to each set of wires one at a time until they are able to communicate. At this point they tell each other what wire they have found and mark the wire for its location.
CAUTION: Do not use this device on energized wires of any voltage, electric shock or death could result.
Step 1: Materials Needed
1) Two phone handsets 1980’s or older will work. (Thrift stores are where I found this set)
2) One 12 DC Switch
3) One 9-volt battery and 9-volt battery snap on leads
4) Wire strippers, wire nuts, wire crimps
5) Razor knife
6) Hack saw or Dremel tool
7) Two sets of test leads
8) Plenty of light and a couple of hours.
9) Small wire nuts
10) Electrical tape
11) Zip ties to secure the battery
Step 2: Getting Started
Twist open the mouth piece so that you can access where the phone cord enters the handset. Once the cover is removed you can see that the phone should be in different parts. Cut the existing phone cord approx 2-inches from the handset and pull the 2-inch wire into the hand set. Discard or recycle the rest of the curly cord. Next, strip the last 1-1/2” of the phone cable so that you can expose the 4-wires that are within the one cord. (2-white wires, 1-Black and 1-Red).
Step 3: Switch and Battery
Take the 12 volt switch and mark a spot on the phone where it can be attached. I attached my switch in the side of the phone as seen in the next couple of pictures. I have seen the switch located on the top, bottom anywhere that the switch has space to be wired. Pending on the age of the phone and the hardness of the plastic a small hack saw may be required to cut out the space. The switch should be either a snap in style or a threaded nut style. With the threaded nut you need to have access to the back of the switch. This is a snap in style, pre-wired and snapped into place. Step 3: Drill a hole in the phone for the 9-volt battery snap leads. These leads will be wired to the existing wiring in the phone.
Step 4: Install Test Leads
Feed and Install the test leads through the hole that the phone cord once was. Tie a knot in the test leads so that they can’t be pulled back out. Do this to both phones. Strip off a ¼” of the insulation using the wire strippers so that you can make up the terminations.
Step 5: Wire Up Phone 1
This is a simple wiring diagram on how to hook up the wiring for the phones.
PHONE 1: From one side of the ear piece, take the white wire to one side of the switch and connect them. From the other terminal of the switch connect to the red (+) battery snap lead. Take the black wire from the battery snap lead and connect it to one of the wires of the mouth piece wire. On the other wire from the mouth piece attach it to the black test lead with either wire crimps or small wire nuts. Now the last wire to be connected on phone #1 is the red test lead to the ear piece wire that hasn’t been used. Once all wires are connected stuff wires back into the phone except the red and black test leads. Reassemble the phone and screw covers back on the mouth and ear pieces. Install the 9-volt battery and secure the battery to the phone with tape or a zip tie.
Step 6: Wire Up Phone 2
Phone 2: The hardest part on the phone assembly is already done, now the handset wiring for the second phone will be a breeze. Take one of the wires from the ear piece and the mouth piece and wire them together. Now take the red test lead and wire it to the remaining ear piece wire. Take the black test lead and wire it to the remaining mouth piece wire. Tuck wires, wire nuts and terminations into the phone and reassemble the ear piece and the mouth piece.
Step 7: Energize
Twist on and verify that all the covers are in place, check the 9-volt battery and make sure you have a charge. Connect the test lead together, (red to red) and (black to black) just like the photograph.
At this point take phone #1 and turn on the switch and bring the phone up to your ear like you are going to have a conversation. Take Phone #2 and tap on the mouth piece, and you will hear the sounds of your tapping in your ear. CONGRADULATIONS!
Step 8: Test and Try
Find a cable to test against, in the next picture there are two sets if wires in this bundle. So I located the plug and inserted the test leads into the plug and then started locating the other end by taking the test leads from the other phone until I heard a clicking noise. At this point in time get assistance from another person and each of you take a phone and have a conversation. (Yes, it may look like kids talking through soup cans)
Step 9: Conclusion
In closing, these phones should be in very tool bag for anyone that works a lot with wiring.
Careers that would use these phones are instrumentation techs, automotive techs, electricians, maintenance people and troubleshooters.