Safety in the Design and Maintenance of Electrical Power Systems

Safety is the cornerstone of all electrical power systems, and it must be an integral part of the design process as well as maintained throughout the system's operational life.

Learning Objectives:

• Understand the codes and standards governing the safety of electrical systems.

• Learn best practices to incorporate into electrical system designs to enhance safety.

• Recognize the safety impacts of proper maintenance of electrical systems.

Electrical Safety Insights

Electrical engineers play a vital role in designing systems that meet the safety standards outlined in various codes. While end-users must always follow safety protocols when working with electrical systems, engineers have the responsibility to ensure that safety measures are embedded into the design of these systems. This includes implementing mitigation strategies for arc flash and other hazards that could jeopardize personnel safety.

Electrical power systems are found across a broad spectrum of buildings, including residential, commercial, industrial, and specialized installations. Each application has unique requirements, but all systems share the same core safety principles.

Electrical Safety Codes and Standards

Design engineers are required to perform code analyses and identify the relevant codes for their projects. This includes national and local codes as well as any federal regulations. In the United States, electrical systems must comply with NFPA 70 (National Electrical Code) to minimize electrical hazards. Engineers must take a holistic approach to system design, considering location, environmental factors, and any hazards that could be present.

Relevant codes include:

• ANSI/NETA MTS: Standard for Maintenance Testing of Electrical Equipment

• NFPA 70E: Standard for Electrical Safety in the Workplace

• NFPA 101: Life Safety Code

• OSHA and other applicable guidelines.

Types of Electrical Hazards

The two main electrical hazards are shock and arc flash hazards, both of which can result in severe injuries, fatalities, and property damage.

• Shock Hazards occur when an electric current flows through an unintended path, including the human body.

• Arc Flash Hazards arise when an electric current is interrupted and causes an arc. The high temperature (up to 35,000°F) of the arc can cause second-degree burns and explosive effects known as arc blast.

The incident energy of an arc flash is a key factor in determining the severity of the hazard. It depends on available fault current, clearing time, and the distance from the arc.

Safety During Design

While meeting minimum codes is essential, engineers should consider additional safety features beyond the baseline code requirements. This may include strategies for easier access to equipment, better protection against hazards, and ways to mitigate arc flash risks.

Some considerations include:

• Double-Ended Distribution Equipment: This setup allows one part of the electrical system to be de-energized for maintenance while continuing to power the building through the other side.

• Remote Operation: For high-mounted or hard-to-reach equipment, remote control options ensure safe operation without the need for personnel to work at height.

• Harmonic Mitigation: Systems with non-linear loads (e.g., motors and uninterruptible power supplies) may require harmonic studies to ensure power quality and prevent damage to equipment.

Arc Flash Mitigation

Arc flash is one of the most dangerous hazards for electricians. There are several strategies to reduce the risk:

• Optical Arc Flash Detection: Using fiber optics to detect the light from an arc flash and immediately trip the breaker.

• Arc-Reducing Maintenance Switch (ARMS): Installed on large distribution equipment, this allows breakers to trip instantly during maintenance, reducing arc flash hazards.

• Remote Racking and Operation: Devices that allow breakers to be operated from a safe distance, thus keeping workers outside the arc flash zone.

Maintenance and Safety

Ongoing maintenance is crucial to the continued safety and functionality of electrical systems. Equipment deterioration over time can lead to failures or hidden faults that may not be detected until a critical moment. Therefore, regular inspections and testing, as outlined by ANSI/NETA MTS-2019 and NFPA 70B, are essential.

Proper labelling of equipment is also critical for safety. Clear labels help identify hazards, ensure correct lockout/tagout procedures, and facilitate quicker fault restoration.

---

Credit to Original Article

This content is adapted from the article "Safety in the Design and Maintenance of Electrical Power Systems," originally published on Consulting-Specifying Engineer.

Written by:

Taha Mohammed is an electrical engineer at CDM Smith, bringing over 20 years of experience in medium- and low-voltage power system design.

Ian Smith is an electrical engineer at CDM Smith, specializing in power system design and protection, as well as communications and SCADA systems.