Twisted pair dialing. Twisted Pair Diagnostics: What Devices Should a System Administrator Have? Now about the tester itself

The message "Network cable is not connected" appeared in the floating window on the computer monitor, the LED on the network card does not light up. Insert, remove the RJ-45 plug in the hope of bad contact in the connection and realize the cable is defective. If you do not have a separate network card installed in your computer, and the network cable plug is inserted directly into the motherboard, then the LED will not light if the connection is disconnected by software.

Nowadays, a twisted pair network cable is often first connected to a router, which sometimes "freezes". Therefore, the first step is to reboot the router. To do this, it is enough to disconnect it from the mains for a minute and then turn it on again. It is quite possible that Internet access will be restored after that.

Disconnection can occur without your direct participation, for example, due to unstable mains voltage, running unlicensed programs or a virus. To check in Win XP you need to go to: Start / Settings / Control Panel / Network connections and make sure the connection is connected. Less often, but it also happens, the driver does not work correctly network card... You can check: Start / Settings / Control Panel / System / Hardware / Device Manager / Network cards... There should be no warning signs.

Network cards very rarely fail, this sometimes happens after a severe thunderstorm. You can check the performance of the network card by connecting it to a known working line or by installing it in another computer, without forgetting to install a driver for it. Sometimes it is possible to make the network card work by swapping it into an adjacent slot motherboard.

Call to technical service the provider will help to check the functionality of the line from their side. If everything is in order in the computer and the provider, therefore, the cable is out of order twisted pairs and its repair is required. You can, of course, call specialists and wait, but if you wish, it is possible to carry out diagnostics and repair the twisted-pair cable with your own hands.

The following twisted pair cable faults are most likely:
- complete breakage of one or more wires - occurs often;
- a short circuit between the conductors of one twisted pair or between the wires of adjacent pairs is less common.

A program for testing access to the Internet
Network Traffic Monitor

IN search engines often looking for the answer to the question: "program for testing twisted pair cable." On a computer with Windows system there is already such a program that displays the message "The network cable is not connected", in the event of a break or short circuit in the twisted pair cable. The place of breakage or short circuit will have to be looked for independently, there is no such program that would indicate exactly the place and cause of the malfunction. There are special testers for this, for example MicroScanner Pro.

It's another matter if there is a connection to the Internet, but it is unstable or the download speed has suddenly dropped. For monitoring network traffic, there is an excellent free program, more precisely, a utility called Network Traffic Monitor.

It allows you to measure the data transfer rate in real time, observe the change in speed over time, save data on the hard drive, rubber windows, wide customization options and many other useful services. Supports many languages, including Russian.

Installing the program on your computer is simple, just run the exe file and press the confirmation button several times. Network will automatically be added to startup and will monitor and save all data. To display any of the windows on the monitor screen, just click right click mouse on the tray icon and select the desired window. Network Traffic Monitor best utility for analyzing and diagnosing the quality of the network from all that I met when searching. I have tested the performance of Network Traffic Monitor with Windows HP and Windows 7. You can download Network Traffic Monitor with one click of the mouse from my website.

Scheme of connecting a computer to a network
utp twisted pair cable

To test a twisted pair cable with knowledge of the matter, it is advisable to present, electrical circuit connecting a twisted-pair cable of a computer's network card with other devices, a hub, a switch or another computer. The figure shows a diagram of a network section for connecting a computer to active equipment, a hub or a switch.

To test the twisted-pair cable, it is of interest just the part of the network card or hub circuit, to which the RJ-45 twisted pair cable connector is connected. As you can see, each pair is connected to the transformer in a symmetrical circuit (a tap is made from the middle of the transformer winding, which is connected to the common wire, sometimes through a resistor or capacitor). Thanks to this connection, all induced noise in the cable arrives at the input in antiphase, and is mutually canceled, and the useful signal arrives in phase and its magnitude does not change. The transformer circuit has another advantage, it protects active equipment from short circuits and entanglement of wires in the twisted pair cable when connected.

The scope and shape of the information signal
twisted pair in cable

Some people have a question, what is the shape and range of the signal in twisted pairs? The presented photograph shows an oscillogram of the information signal. On twisted pairs, both Rx and Tx signals have approximately the same waveform and peak to about two volts. One pair of signals is transmitted, and the other is received, therefore, two pairs are needed for communication. If one of the RJ-45 connectors on the twisted pair cable is removed from the equipment, signal transmission is automatically terminated.

In theory, the signal in a twisted pair should be rectangular, but since there is capacitance and resistance of the conductors, the waveform is rounded. For this reason, the distance between communication points is limited, usually no more than 100 meters. The signal strength of 2 V is not dangerous to humans, not dangerous to network equipment and a short circuit between pairs, so you can troubleshoot a twisted pair cable without disconnecting it from the mains. The network card, switch or hub will not fail.

How to find a break in a UTP twisted-pair cable

There are several ways to find a break in a twisted-pair cable: by external inspection, dialing with a multimeter or a pointer tester, and folk methods.

Checking the twisted pair cable by external inspection

You should start checking the utp cable with an external examination of the cable along its entire length, special attention should be paid to the quality of the crimp in RJ-45 plugs. If crimped inadvertently, the conductors may not be fully inserted into the plug, and the contact will be poor. Or the conductors are overlapped with each other in the place of fixation (it happens with a green pair, since its conductors are crimped at a distance of two contacts) and twisted pairs in this place can be closed. If visual inspection does not reveal a malfunction, then a test of the twisted pair cable should be performed.

If you had at your disposal a modern cable tester with an LCD display, for example, MicroScanner Pro, which allows you to determine not only the type of defect in the twisted pair cable, but also its location, or at least a homemade LED tester, then there would be no questions. However, in everyday life you have to make do with improvised means.

Checking the twisted pair cable with a tester or multimeter

The easiest way to check is the continuity of the orange and green twisted pair with a pointer tester. To do this, you need to remove the RJ-45 plug from the computer's network card. Then, with the test leads of the tester, included in the resistance measurement mode, first touch the orange and white-orange conductors of the twisted pair. The tester should show a resistance of 1-2 ohms, then to green and white-green. Resistance should also be 1-2 ohms. The polarity of the tester connection does not matter. Next, the resistance between the orange and green conductors of the pair is measured. It should be more than 100 ohms, usually equal to infinity. If the measurement results correspond to the above values, then the twisted pairs in the cable are OK.

Here is another method, which is more complicated, but reliable and irreplaceable if the tested twisted pair network cable is not connected to the equipment. It is necessary to bring the ends of the cable with RJ-45 plugs into one place and ring the conductors. It is necessary to set the switch on the device to the position of measuring resistance and, according to the scheme, check the integrity of the conductors and the absence of a short circuit between them.

The photo shows a twisted-pair cable crimped in an RJ-45 connector using color coding option B.

The end of one probe of the device touch the contact of one RJ-45 plug, and with the other probe touch the contact of the same name of the second plug. Resistance should be zero. The wires of each color are called in turn and each wire is checked for a short circuit with any other. A short-circuit test is carried out on one plug. To do this, one end of the probe is connected to a contact, let's say number 1, and the second in turn to all the others. Next, the probe is connected to pin 2 and in turn to 3, 4, 5, 6. Since only two pairs are involved in signal transmission (orange and green, plug contacts 1, 2, 3, 6), then they must be turned to when checking Special attention.

But it is not always possible to bring the utp connectors of the cable to one point. In this case, it is difficult to do without an additional device. Of course, you can lengthen the end of the tester probe for the entire length of the cable and perform the test together, or cut one of the RJ-45 plugs, strip the wires and twist them together in pairs. But it is more expedient to make the simplest device out of an RJ-45 socket, short-circuiting pairs in it with 0.5 mm diameter conductors or resistors, as shown in the photo. Resistors are better, since this will allow you to check not only the integrity of the twisted pair conductors, but also the presence of a short circuit between them. If the measured resistance value is zero, and not installed in the outlet, then the conductors are shorted together. It is better to take different resistor ratings for twisted pair jumpers, for example, 50, 100, 150 and 200 ohms. Then the measurement results will be more informative.

The RJ-45 plug of one end of the twisted-pair cable is inserted into a socket with jumpers, touching the tester's probes to the contacts of the second plug, check each twisted pair in turn and check the absence of a short circuit between adjacent pairs according to the above technology.

Due to the different resistance ratings, it is easy to check the correctness of the twisted-pair crimping when checking the newly made cable. If any pairs are reversed, then by the magnitude of the resistance it will be immediately visible. For example, if, when checking an orange pair, the multimeter shows a resistance of 100 Ohms instead of the prescribed 50, then instead of the orange pair, another pair is crimped into pins 1 and 2 of RJ-45, or the cable is crimped in a different way.

It is very inconvenient to check the twisted pair cable by touching the RJ-45 plug. If a free RJ-45 socket is available, the measurement conditions can be improved. Insert the other end of the cable into the socket and take measurements by touching the contacts inside the socket with the probes.

Based on the results of the check, a decision is made on further actions. If the orange or green pairs are open or closed, then you can replace them with one of the unused ones, brown or blue, if they are working properly. To do this, you will first have to cut off one plug and ring all the pairs again, then the second with a second check of the pairs, since an open or short circuit may be in the plugs themselves. Short-circuits occur in the place where the cable is clamped by the retainer in the plug if the wires are not prepared correctly. Break if the conductors are notched when cutting the outer sheath of the cable. In this place they often break. If, after cutting the plugs, all the pairs turned out to be defective, it is necessary to more carefully inspect the cable along the entire length, if it is not possible to find the damaged place, you will have to replace the twisted pair cable with a new one.

Checking utp cable twisted pair without devices

If you do not have a tester or multimeter at hand, then you can check the serviceability of the twisted-pair cable without them according to the proposed method below. It is necessary to cut off pieces of 10-15 cm from the ends of the cable together with the connectors. Free the ends of the cable from the sheath by 5 cm and remove the insulation from each of the wires to a length of 2 cm.

In a small container made of a dielectric material (glass, plastic, plastic bag), pour a little water with table salt dissolved in it at the rate of a quarter of the volume of salt from the volume of water. The more salt the better. Salt is added to the water to reduce its electrical resistance. Immerse all conductors of one end of the cable in a container with a solution. Each twisted pair can be immersed in turn. The distance between the twisted pair conductors should be minimal, but they should not touch.

Connect the twisted pairs of the opposite end of the cable in series to the poles of any battery or power source with a value of more than 3 V. With a very high salt concentration in the heated water, 1.5 V will be enough.This voltage is given by any finger battery, for example from the remote control remote control TV. A battery from cell phone, it has a voltage of about 3.7 V. The battery from the motherboard will also work, it has a voltage of 3.2 V. If you have a 50-100 ohm resistor, it is better to connect the battery through it to protect the twisted pairs in case of short circuit. The polarity of the connection does not matter.

The telephone network can be used as a power source. Voltage in telephone network about 40 volts and a constant current, limited to telephone exchange 40 mA. Such a connection is safe for humans and telephone line... This option is convenient to use if you need to apply voltage to the twisted pair in the entrance, where there is a telephone box nearby.

Anyone is suitable for verification. Charger from a cell phone, USB port computer, at the extreme terminals there is 5 V. It is not permissible to connect to USB without a current-limiting resistor, you can damage the computer. For testing twisted pairs, a current of 2 mA is sufficient.

After applying voltage, the following picture will be observed at the opposite ends of the twisted pair, which are in the water.

As you can see, on the conductor, which is connected to the negative (cathode), small white bubbles of hydrogen are released, and yellow-green - chlorine, connected to the positive (anode). Obviously, the pair is fine and there is no short circuit with other conductors. In the event of a short circuit, depending on which wire was used, white or yellow bubbles also came from another wire.

If damage is found, then the twisted pair test can be completed at this and the faulty twisted pair can be replaced with a blue or brown one. For example, when checking twisted pairs, an open in the orange pair was detected. Then connect the orange pair from the connectors to the blue cable pair. The connection technology is described on the Twisted Pair Cable Extension page.

Of course, it is better to crimp the cable with new connectors, rather than splicing. Or crimp in the old way described on the page "How to crimp an RJ-11, RJ-45 plug onto a twisted pair cable."

If the orange and green pairs are ok, and you don't want to mess with crimping the connectors, you need to check the cut pieces of cable with connectors. For this, all colored twisted pair wires stripped from insulation and separately white-colored wires are twisted together.

The connector is immersed in the saline solution to such a depth that the contacts are completely submerged in the water. The twisted wires are connected to the battery.

On four of the eight contacts through one, white bubbles should form. Change the polarity of the battery connection, bubbles should form on the contacts on which they did not appear before and also strictly after one. Deviation from this immediately indicates a malfunction. For example, if there are no white bubbles on one of the contacts, then the wire is open, if not on any of the contacts, then there is a short circuit between the conductors. To clarify, you can perform individual testing of pairs by untwisting the previously made twists.

Depending on the results obtained, you will have to engage in crimping or splicing the wires.

Checking a twisted pair cable using a potato

The cable is prepared as described above, only the brine container is replaced with half a potato. Each pair is stuck sequentially into the potato to a depth of 1-1.5 cm. The distance between the conductors should be minimal.

As you can see in the photo, around the wire that is connected to the positive terminal of the battery turned green, and white foam appeared around the negative terminal. When the wires are removed from the potato, you will notice a darkening of the wire to which the minus was applied. If there are no changes on the cut of the potato, it means that the conductors of the twisted pair are open-circuited or short-circuited among themselves.

For the sake of interest, I poked wires into an apple cut. Not so obvious, but that the wires are okay is obvious.

Using the described method of checking a twisted pair, you can check wires of any type, section and length.

A local network with an Internet connection is now available in almost every home. Malfunctions in the network happen, and unfortunately, it is not possible to immediately identify the breakdown. It is necessary to check every component of the network at the software and hardware level.

Algorithm of actions

Let's consider the situation. There is a computer in the room. It is connected with a patch cord to a router, which, in turn, is connected to the provider's equipment using an Internet cable to access the global network. At one point, the network checker program on the computer shows that the connection is unavailable or not connected.

What should be done:

Check the local interface of the computer you are working on - exclude software bugs in Windows or hardware failure of the network card.
Check the operation of the section from the computer to the router - you exclude an interruption in the network on the section of the PC - router, malfunction of the software or hardware of the router responsible for the local network.
Send requests to one or more remote servers of large companies to check the functionality of the cable or equipment that goes and is outside your home.

To walk through the troubleshooting algorithm, work with network commands.

Troubleshooting

A superficial check can be done using the ping all nodes command home network and several remote Internet servers. For these purposes, open command line as administrator. Next, enter the commands, focusing on the algorithm of actions:

Checking the operation of the network card of the computer itself is done by exchanging test packets with itself. If there are no losses, then everything is in order. Team ping 127.1.1.0.

You can add the -t option to keep the packages going indefinitely until you manually stop them with the Ctrl + C key combination.

Then ping the section to the router. It is important to avoid breaking the Internet cable between the computer and the router. If there is packet loss, restart your router and try pinging again. If local IP address the router has not changed, so it is 192.168.0.1 or 192.168.1.1.

When 100% of the number of packets passes to the router, the next step is to ping one of the remote servers. Thus, you can check if there is Internet access. It is recommended to set a ping to the IP address of a large corporation's server, as this excludes the fact that it is unavailable on the network. It is not necessary to know the IP address, you can ping by the domain name.

Analyze the information received.

Fault analysis

We will start from the losses received when sending packets. It is important to understand that the ping command is a protocol of the fourth level of nesting of the OSI model, that is, software, network and hardware errors are excluded, but data levels 5-7 are not checked according to the OSI model.

It turns out that a cable break, if any, can be identified in this way and is the easiest to do. But the programs do not allow you to identify the specific location of the cable breakdown, but only indicate the area.

How to check an Internet cable or local cable and understand that there is a breakage? Eliminate other options related to a malfunctioning network card or router. If there were packet losses when checking the computer itself:

Restart the network connection.
Disconnect from all network add-ons (VPN, proxy).
Do "Network reset".

Update or reinstall the network card driver.

In case of packet loss at the PC site - router:

Reboot your router.
Check that the Ethernet cable connectors are securely seated in the port of the router and the network card (motherboard).
Switch the Ethernet cable to the next port on your router.
Roll back the router to factory settings.

Check the indication of the connected port on the router. If it is off, two options are possible: the capacitors on the router board have malfunctioned (or another hardware failure of the router) or the cable is faulty.

If you lose packets when accessing the Internet:

Reboot your router.
Free up the dynamic IP address in your router settings.

Turn off VPN and proxy.
Ping others remote servers to prevent server unavailability.
Load Internet pages through another browser.
Roll back your router to factory settings.
Call your provider to find out the cause of the problem.

If packets are still not being passed, three reasons are likely: a bad Internet cable, a problem with DNS processing, and a problem with the provider's equipment.

Checking the open-circuit twisted pair and insulation integrity

The following video describes 5 ways to test a twisted pair:

If all indications point to a problem with the cable, it must be identified and corrected. If the short cable fails, you can simply replace it. For wires several tens of meters long, special devices can be used to help identify the problem.

Tester

MicroScanner2 is a professional cable troubleshooting solution. By connecting one connector to the port, the tester will display graphic information about the length of the patch cord to the point of failure.

The rest of the methods require removing the connector and making measurements directly on the contacts of the twisted pair. It will also not be superfluous to make sure of the quality of the cable crimp with the connector. If the crimp is weak or the insulation is broken, problems with signal transmission are guaranteed.

Multimeter

In resistance mode, ring the orange and green twisted pair to check the integrity of the cable:

Remove the second connector from the PC network card or other network equipment.
Remove the connector from the end to be measured and expose the wires.
Apply the tester probes to the orange and white-orange twisted pair wires first. Normal resistance is 1-2 ohms.
Next, attach to green and white-green. The resistance should also be 1-2 ohms. The polarity is not important here.
Then attach the test leads of the multimeter to the orange and green conductors. There should be more than 100 ohms on the multimeter. Usually multimeters indicate infinity.

Regular potatoes

If there were no devices at hand, and you need to find out if the cable is damaged right now, do the following:

Cut the potatoes in half.
Immerse each pair as close to each other as possible in the potatoes 1.5 cm.
If the wire is connected to positive, the area around the submerged conductor will begin to turn green.
If the core is connected to a minus, then a white foam will appear near the conductor. If you pull out the negative wire, it will start to darken.
With zero changes in the state of the potato, the twisted pair is most likely short-circuited or in an open circuit.

Conclusion

In case of problems with access to the global network, you need to identify the cause of the malfunction. It happens that Internet access is blocked because there was a cable break at the site local network or with a patch cord connected to the WAN. It is best to check the integrity of a twisted pair cable using a tester, since it does not require removing the crimped connectors. If there is no such device, use a multimeter or more available methods.

In this article, the author proposes a fairly simple design of a twisted pair test unit. Of course, diagnostics of a twisted pair cable can be carried out with a conventional tester or multimeter, but with the help of this unit, this process will be much faster. This device can diagnose open and short circuit of twisted pair wires. Such a device can be useful for people involved in laying network equipment, setting up computer networks... You can also use it at home to test your network cable or modem cable. When assembling the block, readily available and inexpensive components are used.

Device design:

The device consists of two parts, a passive and an active unit. The passive unit serves for closing the contacts of one end of the twisted pair, and the active unit for supplying voltage and LED indication of malfunctions.

Here is the connection diagram:

Passive block:

In this case, it is made from an RJ-45 socket. Structurally, it consists of a case, a connector and four resistors with a resistance of 400 Ohm each. Each of these resistors connects one of the four twisted pairs and is needed to limit the voltage passing through the circuit.

Active block:

Consists of housing, RJ45 connector, switch, 800 ohm resistor, battery and four diodes.
The body of the device was made from an ordinary plastic cube for children.

A 3-volt CR2032 battery was used as a battery. These are used on computer motherboards (you can use two mini AA or AA batteries, but more space is needed for them). The compartment for its installation was soldered from an unnecessary motherboard.

The cable connector can be removed from a broken network card or other device (modem, router, etc.).
The front panel was drawn on a computer and printed. After being glued on top to improve appearance transparent tape was glued to the device.

The principle of operation of the device:

Both blocks are connected from different ends of the twisted pair. The switch on the active unit is set to position "1". The voltage from the battery inside the unit is fed to the resistor R 5, after which it is fed through the connector to one of the twisted pair wires. Further, passing through one of the resistors of the passive unit, it is fed to the second wire of the twisted pair, comes to the LED and it lights up. By switching the position of the switch to "2", "3" and "4", you can check the remaining pairs of wires.

Diagnosing cable problems:

If the LED is on at normal brightness, there is no problem.

If the LED is on with increased brightness, it is most likely a short circuit between the wires of the twisted pair under test.

If the LED is off, one of the wires of the tested twisted pair is broken.

The author of the article claims that this device can diagnose a cable connected to active equipment (modem, router, network card, switch, etc.). The device will not harm the equipment due to the presence of the R5 resistance in the circuit. Depending on the wiring diagram inside the device, either two or four LEDs will be lit. Thus, you can check the quality of the connections in the equipment connector.

The message "Network cable is not connected" appeared in the floating window on the computer monitor, the LED on the network card does not light up. You insert, remove the RJ-45 plug in the hope of a poor contact in the connection and realize that the cable is faulty. If you do not have a separate network card installed in your computer, and the network cable plug is inserted directly into the motherboard, then the LED will not light if the connection is disconnected by software.

Disconnection can occur without your direct participation, for example, due to unstable mains voltage, running unlicensed programs or a virus. To check in Win XP, you need to go to: Start / Settings / Control Panel / Network Connections and make sure that the connection is connected. Less often, but it also happens, the network card driver does not work correctly. You can check: Start / Settings / Control Panel / System / Hardware / Device Manager / Network cards. There should be no warning signs.

A call to the technical service of the provider will help to check the functionality of the line from their side. If everything is in order in the computer and the provider, then the twisted pair cable is out of order and needs to be repaired. You can, of course, call specialists and wait, but if you wish, it is possible to carry out diagnostics and repair the twisted-pair cable with your own hands.

A program for testing access to the Internet
Network Traffic Monitor

Search engines often look for the answer to the question: "a program for testing a twisted pair cable." In a computer with installed system Windows already has such a program that displays the message "The network cable is not connected" in the event of a break or short circuit in the twisted pair cable. The place of breakage or short circuit will have to be looked for independently, there is no such program that would indicate exactly the place and cause of the malfunction. There are special testers for this, for example MicroScanner Pro.

It's another matter if there is a connection to the Internet, but it is unstable or the download speed has suddenly dropped. To monitor network traffic, there is an excellent free program, or rather a utility called Network Traffic Monitor.

Installing the program on your computer is simple, just run the exe file and press the confirmation button several times. Network will automatically be added to startup and will monitor and save all data. To display any of the windows on the monitor screen, just right-click on the tray icon and select the desired window. Network Traffic Monitor is the best utility for analyzing and diagnosing network quality from all that I met when searching. I have tested the performance of Network Traffic Monitor with Windows HP and Windows 7. You can download Network Traffic Monitor with one click of the mouse from my website.

Scheme of connecting a computer to a network
utp twisted pair cable

To check the twisted-pair cable with knowledge of the matter, it is advisable to present an electrical diagram for connecting a twisted-pair cable to a network card of a computer with other devices, a hub, a switch or another computer. The figure shows a diagram of a network section for connecting a computer to active equipment, a hub or a switch.

The scope and shape of the information signal
twisted pair in cable

In theory, the signal in a twisted pair should be rectangular, but since there is capacitance and resistance of the conductors, the waveform is rounded. For this reason, the distance between communication points is limited, usually no more than 100 meters. The signal magnitude of 2 V is not dangerous to humans, not dangerous to network equipment and a short circuit between pairs, so you can troubleshoot a twisted pair cable without disconnecting it from the network. The network card, switch or hub will not fail.

How to find a break in a UTP twisted-pair cable

There are several ways to find a break in a twisted-pair cable: by external inspection, dialing with a multimeter or a pointer tester, and folk methods.

Checking the twisted pair cable by external inspection

Checking the twisted pair cable with a tester or multimeter

The photo shows a twisted-pair cable crimped in an RJ-45 connector using color coding option B.

Checking utp cable twisted pair without devices

Connect the twisted pairs of the opposite end of the cable to the poles of any battery or power source with a value of more than 3 V. With a very high salt concentration in the heated water, 1.5 V will be enough.This voltage is produced by any finger-type battery, for example, from the TV remote control. A cell phone battery will work well, it has a voltage of about 3.7 V. The battery from the motherboard will also work, it has a voltage of 3.2 V. case of short circuit of twisted pairs. The polarity of the connection does not matter.

The telephone network can be used as a power source. The voltage in the telephone network is about 40 volts and the current is constant, limited at the telephone exchange to 40 mA. Such a connection is safe for a person and a telephone line. This option is convenient to use if you need to apply voltage to the twisted pair in the entrance, where there is a telephone box nearby.

Any charger from a cell phone, a USB port of a computer, at the extreme terminals there is 5 V. It is not permissible to connect to USB without a current-limiting resistor, you can damage the computer. For testing twisted pairs, a current of 2 mA is sufficient.

After applying voltage, the following picture will be observed at the opposite ends of the twisted pair, which are in the water.

Of course, it is better to crimp the cable with new connectors, rather than splicing. Or crimp in the old way described on the page "How to crimp an RJ-11, RJ-45 plug onto a twisted pair cable."

The connector is immersed in the saline solution to such a depth that the contacts are completely submerged in the water. The twisted wires are connected to the battery.

Depending on the results obtained, you will have to engage in crimping or splicing the wires.