Case Study: Pinpointing an Underground Electrical Fault in a Mobile Home Park

Executive Summary

An older mobile home park was plagued by recurring breaker trips from a hidden underground electrical fault. Working across mixed direct‑buried and conduit segments, we isolated the defective span, traced a ground path with transmitter/receiver methods, and marked a precise dig point under a driveway. One targeted cut exposed a moisture‑driven failure on a phase conductor, enabling a fast, surgical repair—without trenching large runs or disrupting residents.

At a Glance

• Site: Older mobile home park with a mix of direct‑bury and conduit feeders
  
• Symptom: Main breaker at switchgear tripping repeatedly; residents temporarily on generator power
• Suspected Route: 600–700 ft down a hillside from switchgear to a transformer, with a mid‑run pull box
• Services: Underground cable fault detection, electromagnetic line tracing, targeted isolation and verification
• Outcome: Fault pinpointed beneath a driveway; one sawcut revealed a blown phase shorted to ground from moisture intrusion; repair completed at the exact failure point

   

Situation

The park’s electrical distribution had evolved over time, leaving a complex blend of direct‑buried cable and conduit‑protected segments. Even after a transformer was isolated and residents were placed on temporary generator power, the main switchgear breaker continued to trip—clear evidence the problem lived somewhere between the switchgear and the transformer. Site staff believed a buried pull box sat mid‑run along the 600–700 ft alignment.

Objective

1. Narrow the fault window without unnecessary excavation.
2. Pinpoint the failure location precisely enough to authorize a single, surgical cut.
3. Restore reliable service with minimal disruption to residents and infrastructure.

Approach

1) Isolate the problem span

We located the mid‑run pull box—an older repair point—opened it, and disconnected/insulated the conductors to prevent arcing. Re‑energizing from the switchgear no longer tripped the breaker, proving the fault was downstream of the pull box in the ~200 ft segment to the transformer (a conduit section).

Why it matters: Isolation prevents “chasing ghosts” and turns a 600–700 ft mystery into a specific span that can be tested methodically.

2) Resolve conflicting test results

Given the conduit, we initially suspected a leg‑to‑leg fault—yet ohm checks leg‑to‑leg read open. To reconcile this, we connected a locating transmitter leg‑to‑ground on each conductor. Two legs produced no traceable tone (expected with an open at the far end), but one leg returned a strong traceable signal, indicating a path to ground.

Why it matters: When resistance checks are inconclusive, transmitter/receiver tracing to ground can reveal real‑world leakage paths that bench tests miss.

3) Confirm from both ends and mark the dig point

We traced the signal to a driveway, where it attenuated sharply—classic behavior where current is bleeding to ground. Repeating the test from the transformer side produced the same attenuation point, confirming the location. The site manager then recalled a past break in that exact area; the prior repair had abandoned the conduit, leaving a direct‑buried splice later overlaid by the driveway. We marked the spot for a single, targeted cut.

Why it matters: Cross‑confirmation from both ends builds confidence for a one‑cut excavation and reduces disruption.

Findings

Opening the driveway at the marked location revealed one phase conductor blown open and shorted to ground, with moisture intrusion at the legacy repair as the root cause. Because the earlier fix did not reinstate conduit, pulling new cable from endpoints was not viable—pinpoint accuracy was the only cost‑effective option.

Results & Impact

• Single sawcut, zero guesswork: The team exposed the exact failure point and completed the repair without exploratory trenching.
• Rapid restoration: Power was brought back to normal service without prolonged outages or repeated digs.
• Controlled cost & disruption: Precision locating minimized demolition, hardscape repairs, and resident impact.

   

Technical Takeaways (for Facility & Electrical Teams)

• Layered networks demand layered diagnostics. Mixed conduit/direct‑bury systems can mask fault modes; leg‑to‑ground tracing can succeed where leg‑to‑leg ohm checks appear clean.
• Legacy repairs are high‑probability zones. Especially where conduit was not reinstated and splices were left direct‑buried under later hardscape.
• Verify from both ends. Matching attenuation points from the switchgear and transformer sides reduces excavation footprints and accelerates repair approvals.

Services Applied

Underground cable fault detection (transmitter/receiver), electromagnetic utility locating and segment isolation, targeted re‑energization and diagnostics.