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Installing underground electrical networks requires the right materials. Using the wrong cable type can cause electrical leakage, short circuits, and serious safety hazards. A common mistake today is using TPS cable underground. TPS cable is only suitable for in-wall wiring and is not designed for direct burial in soil.
This article will help you understand:
- What TPS cable is and its material structure.
- How it works with a three-core system.
- The risks when you bury it directly underground.
- Vietnamese TCVN standards – do they allow this cable for underground networks?
Ngoc Lan Cable also provides recommendations for dedicated underground cables. These solutions help contractors and engineers ensure absolute safety and pass all inspections.
1. What is TPS cable?
TPS (Thermoplastic sheathed cable) is a thermoplastic-sheathed cable. It typically has 2 or more insulated cores wrapped in a protective plastic outer sheath. The most common type is twin cable with an earth wire. The cable is widely used for lighting systems, power outlets, and fixed electrical installations in homes and commercial buildings.
Its flat, compact design and good mechanical protection make TPS cable easy to install. When installed correctly, it also reduces the risk of overheating or short circuits.
2. How does TPS cable work?
TPS cable operates on a closed and safe electrical transmission principle. It delivers electrical energy from the source to the load stably and continuously. With its multi-core structure, this cable supports efficient power transmission and ensures reliable system operation.
2.1. Conductor core structure
In the common twin and earth type, the cable has 3 main parts: the active wire carries electricity, the neutral wire closes the circuit, and a separate earth core. The earth core has no insulation. This design conducts leakage current directly to earth effectively. When a fault occurs (such as insulation failure), this core creates a safe escape path for leakage current. It protects users from electric shock risks.
2.2. Classification by cross-sectional area and current carrying capacity
TPS cable is classified based on copper conductor cross-sectional area. Each size is designed for a specific current load suitable for each application.
- The 1.5mm² type is used mainly for indoor lighting circuits. It can carry a maximum current of 10A. This is enough to supply power for LED lights and fluorescent lamps.
- The 2.5mm² type serves general power outlet circuits. It can handle current loads up to 16A for everyday household appliances.
- Larger cross-sectional types like 4mm² and 6mm² are reserved for high-power equipment. These include air conditioners, electric stoves, and similar devices.
3. Can you use TPS cable underground?
Technically, the answer is no. TPS cable is not allowed for direct burial underground in any case. Here are the main reasons:
Mandatory conditions if you must use it
If you must use TPS cable outdoors, you must install it in dedicated protective conduits (such as HDPE or PVC-U Schedule 40). These conduits must meet load-bearing standards. They completely isolate the cable from impact and pressure from the outside environment.
Burial depth requirements
To ensure safety, the conduit system must be buried at a minimum depth of 600mm below ground level. In areas with frequent heavy truck traffic, this depth must reach at least 800mm. This prevents the conduit from being crushed under surface pressure.
Installation cost and complexity
Using HDPE conduits (DN50–DN100) significantly increases costs. You must also ensure all joints are watertight with proper fittings. Total material costs can be 40–60% higher than using cable alone, excluding labor. Additionally, threading cable through underground conduits is complex and time-consuming. Labor costs can be 2–3 times higher than using dedicated underground cable.
Service life limitations
Even when protected by standard conduits, TPS cable still has service life limitations. The PVC insulation is not suitable for wet underground environments. Service life is typically only around 15–20 years. This is significantly lower than XLPE underground cable (30–40 years). Therefore, this solution increases maintenance costs and forces earlier-than-expected cable replacement.
4. Dedicated underground cables for underground installation
Switching to low voltage underground cables is the correct technical choice. This solution completely eliminates all risks from harsh underground environments.
Superior mechanical protection structure
Dedicated underground cables CVV/DSTA and CXV/DSTA come with integrated steel tape armour (DSTA). This creates a strong mechanical protection layer. As a result, the cable can withstand high soil pressure while maintaining its structure. It allows direct burial without requiring conduits.
Ngoc Lan Cable provides both CVV/DSTA and CXV/DSTA product lines.
Superior thermal performance with XLPE
XLPE insulation on CXV cable allows stable operation at 90°C. It can withstand up to 250°C during short-circuit events for short periods. Compared to the 70°C limit of PVC on TPS cable, XLPE is far superior. With the same cross-sectional area, it can transmit up to 28% more power.
Superior water resistance
Dedicated underground cables have a 5-layer monolithic structure (Conductor → XLPE → Copper Screen → DSTA → PVC Sheath). This completely prevents water penetration. Thanks to its sealed, gap-free design, the cable maintains stable insulation even when submerged for 1000 hours according to IEC 60502-1 standard (>100MΩ). Therefore, the cable operates safely and durably in wet underground environments.
Service life and maintenance
CVV/DSTA cable has a service life of about 30 years. CXV/DSTA with XLPE insulation can reach up to 40 years in standard underground environments. By using the right materials from the start, the system requires almost no mid-life replacement. This avoids major excavation and maintenance costs. This ensures stable long-term operation and optimizes total cost.
5. Frequently asked questions (FAQ)
5.1. Does using TPS cable with plastic conduit provide mechanical durability equal to steel-armoured underground cable?
The answer is no. TPS cable only has a thin PVC insulation layer. Even when placed in plastic conduit, it still has risks. Manually installed conduits are prone to leaks or cracks at joints. This creates a path for groundwater to penetrate.
In contrast, DSTA cable is manufactured with a monolithic multi-layer structure. It integrates completely sealed steel armour directly from the factory. As a result, durability and reliability are superior. This is clearly different from manual assembly solutions.
5.2. How do you choose the right underground cable for your project?
To choose the right cable, consider 3 main factors: operating voltage, load capacity, and geological conditions. For large loads or high-temperature environments, prioritize CXV/DSTA cable. Its XLPE insulation can withstand heat up to 90°C.
In areas with high groundwater or prone to flooding, use cable with DSTA armour and water-tight structure to ensure safety. Consulting with experienced professionals helps you balance investment costs and long-term system durability.
6. Choosing underground cable is the safe and compliant solution
Underground electrical network safety does not compromise on quality. Therefore, choosing the right cable from the design stage is the key to project success.
Important points to remember
- About TPS cable underground: This cable is only suitable for indoor installation with a thin PVC sheath. It cannot withstand underground environments.
- About underground burial risks: Three serious dangers exist – soil and rock pressure, groundwater penetration, leakage current causing short circuits.
- About TCVN regulations: TCVN 5935-1:2013 standard absolutely prohibits direct burial. It requires using conduits if you do not switch to dedicated cable.
- About alternative solutions: CVV/DSTA and CXV/DSTA cables with steel armour withstand pressure well. XLPE insulation withstands heat to 90°C. They save 15-20% total cost and have double the service life.
Ngoc Lan Cable's engineering team is ready to consult on suitable cable solutions according to your project's geological conditions. Contact us now to receive a detailed quotation.
