Splicing electrical wires involves joining two ends of wire together to extend or repair a circuit. For overhead electrical wires, splicing is relatively straightforward. However, splicing underground wires can be more complicated due to limited access and environmental factors. This article will examine if and how underground electrical wire can be spliced.
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Can Underground Electrical Wire Be Spliced?
Yes, it is possible to splice underground electrical wires, but special considerations must be made. Splicing underground wires is more challenging than above ground as the connections need to be waterproof and protected from damage. Improper splicing can lead to system failures, fires, or injury.
Challenges of Splicing Underground Wire
Splicing underground electrical wire presents some unique challenges:
Limited Access
Underground wires are buried and have limited accessibility. Digging to access junction points interrupts surrounding soil/pavement and can be destructive. Care must be taken to precisely locate wires before excavating.
Moisture Protection
Underground wires are surrounded by moisture from soil and water. Splice connections must be completely waterproof to prevent corrosion, short circuiting, and shock hazards.
Damage Prevention
Buried wires are subject to crushing, tension, twisting, etc. Connections need to withstand these forces to avoid detachment or breakage. Strain relief should be applied.
Permanent Connections
Accessing underground connections is extremely difficult. Splices should provide permanent, maintenance-free connections that will last the life of the wire run.
Methods for Splicing Underground Wire
There are several methods for splicing underground wire to create safe, long-lasting connections:
Wire Nuts
Wire nuts are twist-on connectors used to join copper wires. They are not suitable for underground use on their own due to moisture penetration. Wire nuts used underground require waterproof insulating tape over the connection.
Crimp Connectors
Metal crimp connectors join wires by indenting metal sleeves into the wire strands. Crimping tools are used to create compressed connections. The joints then need sealing with insulating putty or tape.
Compression Splices
These pre-filled metal sleeves are positioned over stripped wire ends and compressed with a tool. The sleeve pierces the wires to make the connection, which is sealed within the waterproof sleeve.
Resin Splices
The stripped wire ends are inserted into a mold which is filled with insulating resin that hardens into a durable, sealed connection. No taping required.
Solder Connections
Wires can be spliced by hand-soldering, though this method requires skill. Insulated heat-shrink tubing must be used to seal soldered connections.
Splice Enclosure Types
Underground splices require an enclosure to protect and insulate the connections. Common enclosure types include:
Direct Bury Splices
These sealing capsules are placed over a completed splice and buried directly. No access needed after burial.
Field Assembled Enclosures
A rigid housing is assembled around the splice with handholes for access. Buried after assembly.
Pre-Cast Concrete Splice Boxes
Heavy duty splice boxes are pre-manufactured with a concrete or polymer housing for in-ground installation. Provides protection and space for multiple splice access.
Pedestals
Above-grade splice enclosures provide ready access to junctions without digging. Used where earth burial is difficult.
Proper Splicing Procedures
It is critical to follow proper procedures when splicing underground wires. Key steps include:
Turn Off Power
De-energize and verify wires are powerless before slicing to prevent shock and sparks. Follow lockout/tagout procedures.
Select Suitable Location
Choose a splice location with room to work and proper burial depth. Avoid areas of excess moisture or mechanical damage.
Waterproof Connections
Seal connectors thoroughly using sealing tapes, insulating putty, shrink tubing, or waterproof splice kits.
Insulate Wires
Wrap and insulate all exposed metal surfaces with electrical tape after splicing to prevent shorting.
Install Protective Enclosure
Fully enclose each splice in a suitable box, capsule, or housing unit with adequate slack loops.
Test Circuits
Verify electrical continuity, insulation resistance, and proper function before backfilling.
Backfill and Compact Soil
Carefully backfill and tamp earth around enclosures to avoid damage. Avoid voids.
Common Splice Failure Points
Improper underground splicing can lead to a number of issues such as:
Moisture Intrusion
Leaks into the splice enclosure can lead to corrosion, reduced insulation, and shorting between conductors.
Loose Connections
Vibration and earth movement can loosen unsoldered twist-on connectors over time.
Crushing Damage
Heavy above-ground loads can transfer force and crush buried splice enclosures.
Thermal Expansion Contraction
Temperature changes cause conductors to expand and contract, potentially straining or detaching ill-designed splices.
Erroneous Wiring
Incorrect wiring between conductors can lead to opens, shorts, and reversed polarity.
Excess Pulling Tension
Applying too much tension while pulling wires into enclosures can detach internal splice connections.
Inspection and Testing
All splices should be visually inspected and electrically tested to validate proper installation:
Visual Inspection
Verify proper conductor insertion, tightness of connectors, sealing, strain relief, and overall assembly.
Insulation Testing
Use megohmmeter to validate insulation resistance levels and detect any flaws or moisture intrusion.
Continuity Testing
Check for complete continuity between spliced conductors using ohmmeter. Detect any high resistance joints.
Polarization Index
Compare insulation resistances at 1 minute and 10 minutes to assess connector absorption concerns.
Hi-Pot Testing
Apply elevated voltage to stress insulation looking for dielectric breakdowns indicating weaknesses.
Maintenance and Repair
Periodically inspecting and testing splices enables proactive repair before failures occur:
Annual Inspections
Visually re-inspect for damage, water intrusion, backfill integrity, etc. Thermography can identify hot spots.
Insulation Testing
Trend insulation resistance data annually. Investigate declines that may indicate moisture ingress.
Recondition Damage
Repair housings, replace gaskets, backfill earth, and address other damage noticed during inspections.
Replace Older Splices
Older field-assembled splices may need replacement after 10-15 years to maintain reliability.
Locate and Excavate
For failed splices, carefully locate the junction, excavate the enclosure, and complete repairs.
Conclusion
Splicing of underground wire is an essential practice for installing, extending, and maintaining underground electrical systems. While challenging, following proper procedures for waterproofing, insulating, enclosing, and testing splices enables reliable performance. When done correctly, underground wire splices can last for decades before needing repair or replacement. Regular inspection and maintenance identifies issues for correction before they lead to failures.
| Splice Type | Description | Sealing Method |
|---|---|---|
| Wire Nuts | Twist-on wire connectors | Waterproof tape |
| Crimp Connectors | Compressed metal sleeves | Insulating putty/tape |
| Compression Splices | Pre-filled metal sleeves | Self-contained within sleeve |
| Resin Splices | Wires encased in insulating resin | Self-contained resin |
| Solder Connections | Hand soldered junctions | Heat shrink tubing |
| Splice Enclosure | Description |
|---|---|
| Direct Bury | Encapsulate splice and bury |
| Field Assembled | Construct enclosure around splice |
| Concrete Splice Boxes | Pre-manufactured heavy duty enclosure |
| Pedestals | Above grade access point |
| Inspection / Testing | Purpose |
|---|---|
| Visual Inspection | Check assembly, seals, connections |
| Insulation Testing | Detect moisture intrusion |
| Continuity Testing | Find high resistance connections |
| Polarization Index | Assess connector absorption |
| Hi-Pot Testing | Stress insulation for weaknesses |