Recent work examining the effectiveness of various technologies used to improve resilience and wildfire performance has shown that utilities rank placing lines underground in the top two approaches.

Across the utility industry, this has led to undergrounding as one of the main preferences. However, the locations chosen for wildfire mitigation, public safety, and right‑of‑way often means that conventional trenching is slow, expensive, or simply impossible.

Rocky terrain, contaminated soils, and environmentally sensitive corridors are just a few of the complicating factors which can push excavation timelines and costs far beyond those typically seen.

Ground‑Level Distribution Systems (GLDS) provide a solution to the complicating factors of terrain by challenging the long‑standing assumption: that underground cables must always be buried deep to be protected. Instead of relying on burial depth for protection, GLDS provides the same performance with layers of engineered mechanical protection (NESC Rule 352D) allowing medium‑voltage (MV) cables to be installed at or near the surface.

What Is GLDS?

A GLDS installation places MV cables inside conduits, usually in the form of Cable in Conduit (CIC), that are restrained within a plastic sectional rail system, anchored to the ground. A flame‑retardant thermoplastic top and bottom plate form the outer protective envelope into which an engineered geo polymer concrete is poured to fully encapsulate the conduits

A closely related variant, the Minimum Cover Distribution System (MCDS), uses the same structure coupled with a shallow burial within the topsoil when limited cover is preferred in cases such as roadway crossings or aesthetics or capacity. This embodiment supports flexible depths (typically around 6 - 15 inches) and does not require excavation of the subsoil.

A number of early field pilots at DTE / EPRI / PG&E have demonstrated the constructability of the concept, however constructability is not the only important question that utilities are asking: these questions include Will a surface‑installed system survive real‑world abuse? Will cables within GLDS operate differently to conventional direct buried approaches.

Purpose‑Built Testing

To answer these questions, EPRI and its utility collaborators constructed a number of full‑scale GLDS installations at its Lenox Laboratory. These were designed specifically for engineering and scientific research rather than demonstration. Testing focused on 2^nd Generation GLDS, incorporating high strength, water free, geopolymer concrete and non‑metallic rebar to improve impact resistance and durability.

The testing program evaluated four primary risk categories utilities worry about most:

• Vehicle traffic
• Falling‑weight impact
• Ground fire exposure
• Thermal performance and ampacity

Vehicle Impact

One of the most visible concerns with the surface installation of GLDS is the increased potential exposure to vehicles, particularly in roadside and right‑of‑way installations In testing, GLDS sections were repeatedly driven over by vehicles ranging from pickup trucks to heavy transmission utility trucks weighing more than 17 metric tons.

The reinforced GLDS sections showed:

• No damage to the cable conduits
• No damage to the plastic top plates or anchors
• No cracking or loss of function of the geopolitical polymer concrete encapsulant
• No conduit distortion under repeated direct and glancing impacts

Analysis of cumulative loading suggests that even very heavy vehicles would need to strike the same location many times before damage would be expected—an unlikely real‑world scenario.

Falling‑Weight Impact

To simulate dropped tools, debris, or tree strikes, EPRI developed a repetitive falling‑weight test using a 9‑kg steel sphere dropped from 1.2 meters onto the same point on the GLDS structure. The results clearly differentiated encapsulation materials.

• Reinforced geopolymer concrete required roughly two dozen impacts to initiate cracking and more than 40 impacts before repair was needed
• Traditional Portland cement concrete, such as that used in conventional duct banks cracked in as few as two impacts and required repair after roughly ten

The takeaway for utilities is straightforward: not all concrete performs the same, and reinforcement strategy is critical when burial depth is removed.

Wildfire Exposure

Wildfire mitigation is one of the strong drivers for undergrounding through the reduced chance of vegetation ignition. However, wildfires may interact with a GLDS installation; testing addressed this survivability directly. At Lenox, GLDS sections were subjected to controlled ground‑fire events (>20) using straw and wood fuel loads representative of dry‑season conditions.

Key findings included:

• Flame‑retardant top plates did not ignite or sustain combustion
• Geopolymer concrete encapsulant showed no degradation - unlike conventional concrete the absence of structural water avoids thermal spalling
• Conduit temperatures increased by no more than ~1.5 °C, even after repeated burns - due to the thermal properties of the geoploymer concrete

Thermal Performance and Ampacity

Unlike a typical direct buried configuration, where heating comes only from the conductor, cables within GLDS are exposed to additional energy input from solar radiation. Moreover heat transfer is impacted by the ambient air temperature rather than the more usual ground temperature. Extensive thermocouple instrumentation on cables within the conduits at Lenox measured temperatures at the conductor, conduit, encapsulant, and top plate under real environmental conditions.

Results showed that:

• GLDS ampacity is influenced by ambient temperature and solar irradiance and this is highly location specific
• For much of the year, ampacity is comparable to conventional buried conduit installations
During peak summer conditions, some derating may be required, depending on location

Opportunities for Deployment

Based on the testing and early utility deployments, it is believed that GLDS is well suited for:

• Wildfire‑prone corridors where trenching is impractical
• Rocky or contaminated ground
• Environmentally or archaeologically sensitive areas
• Temporary or rapidly deployable urban MV circuits
• Substation environments where excavation disrupts grounding systems

From Test to Field

Phase I testing at Lenox confirms that modern GLDS designs are mechanically robust, fire‑resistant, and electrically viable when properly engineered. It is anticipated that ongoing research will address performance in minimum cover applications, long‑term aging, freeze‑thaw exposure, cable jointing and multi‑phase magnetic fields, but the evidence to date supports broader pilot deployments.

There is little doubt that GLDS represent an expanded capability and shift in mindset for utilities facing growing pressure to underground faster and with less disruption: engineered protection can substitute for excavation depth when the performance is proven by testing.

Acknowledgments

This article was also prepared with the contribution of Connor Duffy, PPL; Louie Mercurio, SCE; Marizol Perez Cruz, SDG&E; and Henry Wilson-Sowah, CHE.