USPS P&dc MECHANICAL & ELECTRICAL UPGRADES

This project was a firm fixed contract to install new rooftop heating and cooling units for the entire USPS PDC building. As part of this upgrade, the existing electrical system was enhanced to accommodate the increased load demands, while ensuring continuous facility operations with minimal interruption.

Electrical System Upgrades

The main electrical system consisted of four 4160/480-volt double-ended switchgear units. As part of the project, existing 4160/480-volt dry-type transformers were upsized from 750 KVA to 1250 KVA to support the new HVAC equipment and associated loads.

Medium Voltage Infrastructure

The existing medium-voltage cable was removed and replaced with new 5KV 500 MCM copper cable to reliably service the upgraded electrical demand. All installations were carefully executed to ensure performance, durability, and compliance with system requirements.

Load Transfer Strategy

To minimize operational disruptions, the Peachtree Mechanical Electrical Division implemented a strategic load transfer process. Loads were shifted from one end of the double-ended switchgear to the other by opening the main breaker on one side and closing the tie breaker. This process was completed in under 15 minutes, allowing the facility to remain operational with minimal interruption.

Transformer Replacement Process

Once loads were transferred, the existing 750 KVA transformer was removed and replaced with a new 1250 KVA unit. The newly installed 500 MCM 5KV cable was then terminated, tested, and energized. This process was repeated for the opposite end of the switchgear and across all units in the facility.

Panel and Breaker Installation

New 600-amp MLO panels were installed to support additional loads and facilitate the transfer of existing loads from MCC units. These panels were fed by new 800-amp breakers with adjustable trip settings, installed within the existing switchgear. As these were draw-out type breakers, new cradles were installed and the existing bus system was modified to accommodate the upgrades.

Planned Outage Execution

While most work was completed with minimal disruption, an 8-hour outage was required to finalize portions of the upgrade. This outage was strategically scheduled during holiday weekends to avoid any impact on mail processing operations.

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