When digging in your yard, it is important to be aware of the potential hazards. One such hazard is buried cables. If you accidentally hit a cable while digging, you could be in for a dangerous shock. So, how can you tell if a cable is buried live? Keep reading to find out.
Steps before digging
- Contact your local utility company to have them mark any underground cables on your property. This service is typically free and can help you avoid hitting a live cable while digging.
- Review any plans or diagrams of your property that show the locations of buried cables. If you are unsure about the accuracy of these plans, contact the utility company to confirm their locations.
- Use caution when digging near any marked lines on these plans. These lines represent the approximate location of buried cables and should be avoided.
- Use a metal detector, or an underground cable locator to scan the area you plan to dig in. It will help you locate any buried metals, including cables.
- If you do not have a metal detector, you can try using a long rod or stick. Gently poke the ground in the area you plan to dig, feeling for any hard objects.
- Use a shovel to dig a hole that’s at least 12 inches deep and 18 inches wide to see what’s in the ground before you start digging.
- Once you have located a buried cable, stop digging immediately and do not attempt to move or remove it yourself. Instead, contact your local utility company for assistance.
Methods of testing if a cable is live
Ground resistance testing
Ground resistance testing is the most common method of testing for live cables. This method involves sending an electrical current through the soil and measuring the resistance.
You will need a ground resistance meter, also known as an earth tester, to conduct a ground resistance test. These meters are available for purchase or rental from most hardware stores.
Before you begin the test, make sure that the area around the buried cable is clear of any vegetation or debris. It will ensure that the current can flow freely through the soil.
Once the area is clear, connect one lead of the ground resistance meter to the buried cable. Connect the other lead to a metal rod driven into the ground at least 10 feet away from the cable.
Turn on the meter and note the reading. If the reading is less than 10 ohms, the cable is live, and you should not attempt to dig it up yourself. Instead, contact your local utility company for assistance.
Voltage testing
Voltage testing is another common method of testing for live cables. This method involves measuring the voltage of the cable using a voltmeter.
To conduct a voltage test, you will need a voltmeter to measure AC voltage. These meters are available for purchase or rental from most hardware stores.
Clear the area around the cable. Touch one lead of the voltmeter to the buried cable. Touch the other lead to a metal rod at least 10 feet away from the cable.
Note the reading on the voltmeter. If the reading is more than 50 volts, the cable is live, and you should not attempt to dig it up yourself.
If the voltmeter reading is less than 50 volts, the cable may be live or may be dead. To confirm, repeat the test with the meter set to a higher voltage setting. If the reading is still less than 50 volts, the cable is most likely dead, and you can proceed with digging.
Megger testing
Megger testing is a more sophisticated method of testing for live cables. This method involves sending a high-voltage current through the cable and measuring the resistance.
To conduct a megger test, you will need a megger machine available for purchase or rental from most hardware stores.
Follow the manufacturer’s instructions to set up the megger machine. Once the machine is set up, touch one lead of the machine to the buried cable. Next, touch the other lead to a metal rod that is at least 10 feet away from the cable.
Note the reading on the megger machine. If the reading is more than 0.5 ohms, the cable is live, and you should not attempt to dig it up yourself.
If the megger reading is less than 0.5 ohms, the cable may be live or may be dead. To confirm, repeat the test with the machine set to a higher voltage setting. If the reading is still less than 0.5 ohms, the cable is most likely dead, and you can proceed with digging.
Insulation resistance testing
This method involves sending a low-voltage current through the cable and measuring the resulting voltage drop. To conduct an insulation resistance test, you must purchase or rent an insulation resistance tester from a hardware store.
Once you have set up the machine, touch one lead of the machine to the buried cable. Then, touch the other lead to a metal rod that is at least 10 feet away from the cable. If the reading from the insulation tester is more than 1 megohm, that means the cable is live.
Do not try to dig it up yourself. Contact your local utility company for help instead.
If the insulation tester reading is less than 1 megohm, the cable may be live or may be dead. To confirm, repeat the test with the meter set to a higher voltage setting. If the reading is still low, the cable is most likely dead, and you can proceed with digging.
Non-contact voltage testers
This method involves using a device that beeps or flashes when it detects a voltage in the cable. To conduct a non-contact voltage test, you will need a non-contact voltage tester. These are available for purchase or rental from most hardware stores.
Turn off all power to the area where you will be testing. It includes any circuit breakers or fuses that supply power to the area. Select a non-contact voltage tester and hold it near one end of the cable you wish to test.
If the voltage tester lights up or makes a sound, the cable is live and should not be disturbed.
If the voltage tester does not register any voltage, the cable is most likely safe to dig up. However, you should still use caution as there may be other cables in the area that are live. Always err on the side of caution and contact your local utility company for assistance if you are unsure whether a cable is live.
Digital Multimeters
This method involves sending a low-voltage current through the cable and measuring the resulting voltage drop.
Select a digital multimeter and touch one probe to each end of the cable you wish to test.
Set the digital multimeter to the “DC Voltage” setting and note the reading.
If the reading is more than 1 volt, the cable is live, and you should not attempt to dig it up yourself. Contact your local utility company for assistance.
If the digital multimeter reading is less than 1 volt, the cable may be live or dead. Repeat the test with the meter set to a higher voltage setting. If the reading is still less than 1 volt, the cable is most likely dead, and you can proceed with digging. However, it would help if you still used caution as there may be other cables in the area that are live.
Safe digging around a buried cable
- Turn off all power to the area where you will be working. It includes any circuit breakers or fuses that supply power to the area.
- Locate the buried cable using a voltage tester or another method.
- Once you have located the buried cable, use caution when digging around it. Avoid touching the cable with your bare hands or any other objects.
- If you must dig through the buried cable’s area, use a shovel or other tool to dig a trench around the cable. Be careful not to damage the cable while digging.
- Once you have finished digging, fill the trench and restore power to the area.
What should I do if I hit a live cable while digging?
- If you hit a live cable while digging, stop immediately and do not attempt to move or remove the cable yourself.
- Evacuate the area and keep people and pets away from the area until the utility company arrives.
- Call your local utility company and report the incident.
- Do not turn on any lights or appliances in the area until the utility company has inspected the area and determined it is safe to do so.
- If you experience any symptoms of electrical shock, such as tingling, numbness, or muscle spasms, seek medical attention immediately.
