Wiktor Wise
Repairing an underground electrical line can be a challenging task due to the high voltage involved and the potential dangers associated with it. It is essential to exercise extreme caution and follow safety protocols to ensure a successful repair. The first step is to locate the break in the underground line, which can be done with the help of an electrician using specialised equipment such as ground-penetrating radar or time-domain reflectometry. Once the break is located, the next step is to excavate the area and expose the damaged cable. At this point, it is crucial to turn off the main electrical supply to prevent any accidents. The repair process typically involves using an underground splice kit, which comes in two varieties: heat-shrinkable tubing and gel-filled shields. These kits provide a water-resistant connection and protect the splice from corrosion and moisture. It is important to closely follow the manufacturer's instructions when using these kits. In some cases, it may be necessary to replace the entire section of the damaged cable with a new one of the same gauge. This process requires cutting, stripping, and properly connecting the wires using the splice kit.
| Characteristics | Values |
|---|---|
| First Steps | Turn off the main electrical supply before attempting any repair. |
| Locating the Fault | If the location of the break is unknown, hire an electrician with an underground open/short locator. Alternatively, try ground-penetrating radar, time-domain reflectometry, or a device called a thumper. |
| Repair Method | Use an underground splice kit, which typically includes heat-shrinkable tubing and a gel-filled shield. For low-voltage wiring, use low-voltage connectors for direct burial. |
| Additional Tips | Purchase waterproof junction boxes to protect connections from corrosion due to moisture. Ensure the wiring is deep enough to avoid damage from gardening tools. |
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What You'll Learn
Locating the fault
Cable Thumping:
This method involves using a cable thumper or surge generator to inject a high-voltage DC surge into the faulty cable. The surge creates a high-current arc at the exact location of the fault, producing a characteristic thumping sound. By repeatedly thumping and walking along the cable route, the fault can be located. Cable thumping is accurate and easy to apply and learn. However, it can be time-consuming for longer cables and may weaken the insulation of the cable due to frequent high-voltage surges.
Time Domain Reflectometry (TDR):
TDR sends a low-energy signal into the cable, causing no degradation to the cable insulation. It works well for open-circuit faults and conductor-to-conductor shorts. However, TDR provides an approximate distance to the fault location rather than an exact pinpoint and may be affected by surrounding electrical noise.
A-Frame Fault Finder:
Technicians use this equipment to locate the exact place that needs repair and indicate the severity of the fault. It works by applying an 8K frequency to the power or telecom cable.
Section Testing:
Crews isolate a section of the cable and apply a DC hipot voltage. If the cable holds the voltage, they move on to the next section until they find a cable that cannot hold it. A faster variation involves using high-voltage sticks that apply a DC voltage to the isolated section.
VLF HI-POT TEST:
This method is suitable for long-length cables. It involves applying a very low frequency (VLF) voltage to the cable for a specified duration. The voltage and frequency values depend on the cable's specifications.
Murray and Varley Loop Tests:
These are popular techniques for locating faults in underground cables, but specific details about their implementation are not readily available.
It is important to note that locating underground cable faults requires specialized equipment and expertise. Engaging professionals with the right tools, such as The Underground Detective or electrical professionals, can save time and money by accurately pinpointing the location of the fault.
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Using a splice kit
If you are repairing an underground electrical line, you can use a splice kit to fix it. Before you begin, make sure you turn off the main electrical supply. If you don't know the location of the break, you can purchase electronic locating equipment or phone your local electric company and use their locating service.
Underground line-voltage splice kits come in two varieties: heat-shrinkable tubing and gel-filled shield. Both use a brass splicing block to connect the wires but differ in how they protect the splice. Be sure to closely follow the manufacturer’s instructions. The most common type of kit protects the splice with a length of heat-shrinkable tubing filled with watertight hot-melt adhesive.
Before using the splice kit, cut the damaged wiring on either side of the break and strip back the outer sheathing and the wire insulation. Slide the heat-shrink tube over one end of the cable, then connect the wires to the brass connector. Do this on both ends of the new cable. Once the wires are joined with connectors, slide the heat-shrink tube over each connector and heat it with a heat gun until it shrinks.
If you are adding circuitry to your existing wire underground, you can use a splice kit with an inline connector to join the two ends of a break securely in a polyolefin sleeve. This will shrink when heated to maintain a water-resistant connection. You can also use a direct burial splice kit, which uses butt splices and electrical tape to cover the splice.
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Waterproofing the connection
Another option is to use low-voltage connectors designed for direct burial. These connectors rely on gel to encapsulate the splice and prevent water intrusion and corrosion. For low-voltage stranded cable, such as lighting cable, a wire nut/gel-filled tube style connector can be used. The wire nut is twisted on, and then the connector is plunged into the tube until the gel oozes out the top. For solid irrigation and telephone wires, an insulation-piercing gel-filled connector can be used by simply pushing the wires into the connector and snapping it closed.
Additionally, waterproof junction boxes can be purchased to protect connections from moisture and corrosion. These boxes provide a waterproof seal for the electrical wiring that enters the box, ensuring that the connections remain dry and protected from the elements.
For deeper wiring, a splice kit with an inline connector can be used to join the two ends of a break securely in a polyolefin sleeve. When heat is applied, the sleeve shrinks, creating a water-resistant connection. The adhesive liner inside the tubing melts when heated, coating the connection and covering the wire with adhesive.
It is important to closely follow the manufacturer's instructions when using any of these waterproofing methods to ensure a safe and effective repair.
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Replacing the cable
Before you begin replacing the underground electrical cable, make sure you turn off the main electrical supply. Then, use a non-contact voltage tester to confirm that the cable is no longer live. If you are unsure about where the break is, it is best to hire an electrician with an underground open/short locator to locate and mark the cable.
Once you have located the break, dig along the cable's path between the exit and entry points. Cut the cable about 12 inches on either side of the break. Then, strip back the sheathing by 2 inches and the wire insulation by 5/8 inch. Cut, separate and strip the ends of the buried cable.
Use an underground splice kit to connect the new cable section. There are two types of kits available: heat-shrinkable tubing and gel-filled shield. Both use a brass splicing block to connect the wires. However, they differ in how they protect the splice. Be sure to closely follow the manufacturer's instructions.
With the heat-shrinkable tubing kit, slide the tubing over the cable before connecting the wires to the splice block. Once the wires are connected, slide the heat-shrink tube over each connector and heat it with a heat gun until it shrinks tight on the connector and sealant starts bubbling out of the end.
For the gel-filled shield kit, twist on the wire nut and plunge the connector into the tube until the gel starts oozing out of the top. Then, snap the lid closed.
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Hiring an electrician
Repairing an underground electrical line is a complex and potentially dangerous task, so it is always best to hire a licensed electrician with experience in underground electrical work. This type of work falls under the career category of electrical power-line installers and repairers, so it is important to seek out professionals with this specific skill set.
When hiring an electrician to repair an underground electrical line, there are several key factors to consider. Firstly, ensure that the electrician has experience in locating and repairing underground cables. They should be able to locate and mark the cable, determine its depth, and pinpoint the exact location of the problem. This may require the use of specialised equipment such as an underground open/short locator.
Secondly, discuss with the electrician the specific repair methods they plan to use. Underground electrical repairs often involve splicing the cable, and there are different types of splice kits available, such as heat-shrinkable tubing or gel-filled shield kits. The electrician should be familiar with these kits and be able to advise on the most suitable method for your specific situation.
Additionally, consider the scope of the project and whether you may need to hire additional professionals. Underground electrical repairs can be complex and may require trenching, conduit installation, and cable running. In some cases, a general contractor may be needed to manage the project and coordinate with any necessary subcontractors.
It is also important to obtain multiple quotes from different electricians and compare their pricing, experience, and proposed repair methods. Discuss the costs involved, including labour, materials, and any required permits or inspections. Ask for references from previous clients who have had similar underground electrical repair work done, and ensure that the electrician is licensed, insured, and adheres to all relevant safety practices and procedures.
Finally, remember that electrical work, especially underground electrical repairs, can be dangerous and should not be attempted as a DIY project unless you have the proper licensing and skills. Always prioritise your safety and that of your property by hiring a qualified and experienced electrician.
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Frequently asked questions
First, turn off the main electrical supply. Then, use a non-contact voltage tester to confirm that the cable is no longer live.
Locating a fault in an underground line is a challenging task. You can use ground-penetrating radar, time-domain reflectometry, or a device called a thumper. Alternatively, hire an electrician with an underground open/short locator to locate and mark the cable.
You will need an underground splice kit, which typically includes heat-shrinkable tubing or a gel-filled shield to protect the splice. You may also need waterproof junction boxes and special sealing box cable connectors if you are adding additional circuitry.
Cut the damaged cable on both sides of the break and strip back the outer sheathing. Insert each conductor into the connector, matching the colours. Tighten the screws and heat the shrink tube with a heat gun to seal the connection.
