Current Unbalance & Flood Remediation

Client: Institutional Multifamily Portfolio (Confidential)

Location: South Bay, CA (High-Density Urban Asset)

Project Focus: 3-Phase Electrical Diagnostics, NEMA Unbalance Analysis, and Sub-Grade Flood Mitigation

Background

The asset is a luxury high-rise residential complex featuring a sub-grade parking garage serviced by a critical duplex sewage ejector system. The system utilizes 3-phase submersible pumps. Following a period of heavy usage, the system experienced a total lockout, resulting in a sewage pit overflow and significant flooding of the subterranean resident parking level.

Identified Issues

1. Catastrophic Overflow: The failure of the "Auto" control logic led to a high-level alarm bypass and subsequent garage flooding, creating immediate health, safety, and liability concerns.

2. Thermal Overload Tripping: Preliminary inspection showed that Pump B was intermittently tripping its thermal overloads, despite the pump being less than 24 months old.

3. Ineffective "Standard" Troubleshooting: Previous attempts by general plumbing contractors focused solely on clearing potential "clogs" without addressing the electrical root cause, leading to recurring system instability.

Control System Analysis & Data-Driven Diagnostics

1. NEMA Current Unbalance Audit (The Professional Distinction)

• Issue: Rather than simply checking for "rotation," we performed a NEMA-standard current unbalance test.

• Data Captured:

  • L1: 18.2A | L2: 21.5A | L3: 17.4A

  • Average: 19.03A

  • Max Deviation: 2.47A (L2)

  • Calculated Unbalance: 12.98% (Exceeding the 10% maximum allowable threshold).

• Result: This 13% unbalance was causing a 25% increase in winding temperature, explaining the intermittent thermal tripping and identifying the "why" behind the system failure.

2. Phase Rotation Root Cause Analysis

• Issue: It was necessary to determine if the unbalance originated from the pump motor or the building’s power supply.

• Action: Performed a "Phase Rotation Test" by rolling the motor leads at the starter.

• Discovery: The high current followed the power leg, not the motor lead. This proved the issue was a "high-resistance connection" within the aging control panel’s contactor set, not a faulty pump.

• Professional Impact: This prevented the client from unnecessarily spending $6,500 on a new pump motor that would have failed again within months.

3. Remediation of Submersible Junction Box

• Issue: Inspection of the pit-side junction box revealed water intrusion that was "shorting" the low-voltage sensor signals.

• Action: Replaced existing connections with NEMA 6P-rated submersible gel-cap connectors and re-sealed the conduit run with duct seal to prevent "chimney-effect" moisture migration.

• Result: Restored 100% signal integrity to the float and alarm logic.

Outcome

The sewage management system was restored to full operational status with:

• Verified Electrical Balance: Post-repair unbalance was reduced to 2.4%, well within safe operational parameters.

• Flood Prevention: Corrected the "Auto" logic failure that led to the garage flood, ensuring high-level alarms now trigger immediate lag-pump activation.

• Cost Savings: Saved the client the cost of a premature pump replacement through data-validated electrical troubleshooting.

Recommendations

• Quarterly Electrical Audits: Implement a PM schedule to record Amperage draw and calculate unbalance to identify terminal corrosion before it leads to a lockout.

• Infrared Thermography: Perform annual thermal imaging on the control panel to identify "hot spots" in contactors and breakers.