What is PEPC on Boeing 737? (Primary External Power Contactor)

In the complex world of aviation, aircraft systems play a crucial role in ensuring safe and efficient operations. One such system that is of utmost importance on the Boeing 737 aircraft is the Primary External Power Contactor, commonly known as PEPC. This article will delve into the functions and significance of the PEPC, shedding light on its role in powering the aircraft.

The Primary External Power Contactor (PEPC) on the Boeing 737 is a device designed to control the flow of external electrical power to the aircraft. It acts as a gatekeeper, allowing or disconnecting the power source from the aircraft’s electrical system. This ensures that the external power is only utilized when necessary, while also protecting the aircraft’s electrical components from potential damage.

The PEPC is located in the electrical power distribution panel, which is situated in the avionics compartment of the aircraft. It is connected to the ground power receptacle, where the external power source is plugged in. When the ground power unit is connected, the PEPC activates and establishes a connection between the external power source and the aircraft’s electrical system.

The PEPC plays a crucial role during various phases of flight, including pre-flight, ground operations, and maintenance. Let’s explore its functions in more detail.

The Functions of the Primary External Power Contactor

1. Powering Pre-Flight Electrical Systems

During pre-flight preparations, the aircraft undergoes numerous checks to ensure all systems are functioning properly. One of these checks involves powering up the electrical systems to perform tests and diagnostics. Instead of relying on the aircraft’s onboard power generation system, external power can be used to provide sufficient electrical supply for these checks.

The PEPC facilitates this process by allowing the connection of the ground power unit to the aircraft’s electrical system. It ensures that the external power is efficiently distributed to the appropriate systems, enabling pilots and maintenance personnel to perform necessary tests and inspections, ensuring the aircraft is flight-ready.

2. Supporting Ground Operations

During ground operations, the aircraft relies on various electrical systems to power essential functions such as cabin lighting, air conditioning, and ground communication. Using the aircraft’s onboard power generation system for these operations may consume a significant amount of fuel, especially during prolonged ground stays.

By connecting the aircraft to an external power source through the PEPC, the aircraft’s electrical systems can be powered without relying on the internal power generation system. This helps conserve fuel and reduce emissions, contributing to a more sustainable and cost-effective ground operation.

3. Assisting with Maintenance Procedures

Maintenance procedures on the Boeing 737 often require electrical power to be supplied to specific systems or components. These procedures may involve testing, troubleshooting, or repairs. During such situations, the PEPC acts as a vital component in providing the necessary external power to the designated areas.

By isolating and controlling the power supply through the PEPC, maintenance personnel can safely test systems without needing to rely solely on the aircraft’s internal power generation system. This enhances the efficiency of maintenance procedures and reduces the risk of potential electrical issues or malfunctions during the testing process.


The Primary External Power Contactor (PEPC) on the Boeing 737 aircraft plays a critical role in ensuring the electrical systems are powered safely and efficiently. From pre-flight preparations to ground operations and maintenance procedures, the PEPC facilitates the connection between external power and the aircraft’s electrical system.

By utilizing the PEPC, pilots, maintenance personnel, and ground operators can benefit from a reliable and convenient power source, reducing the reliance on the aircraft’s onboard power generation system and optimizing fuel consumption. The PEPC is a key component in maintaining the operational integrity of the aircraft’s electrical system, contributing to overall flight safety and efficiency.

Understanding the functions and significance of the PEPC allows individuals involved in aviation to appreciate the intricacies of aircraft systems and the role they play in ensuring smooth operations. With the Primary External Power Contactor, the Boeing 737 maintains its position as a reliable and advanced aircraft in the aviation industry.

For more information about the Boeing 737 aircraft and its systems, visit Boeing’s official website.

For More: What is EGPWS on Boeing 737? (Enhanced Ground Proximity Warning System)