Navigating OSHA 269 Transient Overvoltage (TOV) Requirements: Engineering Analysis and Mitigation Strategies

The Occupational Safety and Health Administration’s updated 29 CFR §1910.269 regulations on transient overvoltage (TOV) have reshaped how utilities define Minimum Approach Distances (MAD) for systems above 72.5 kV. Since the update took effect on January 31, 2016, utilities must either assume OSHA’s default conservative TOV values or conduct a customized engineering analysis to determine actual TOV magnitudes

At Keentel Engineering, we specialize in conducting these studies using PSCAD or EMTP-RV to help utilities maintain safe yet practical MADs while ensuring full OSHA compliance.

Understanding the OSHA 269 Mandate

Under the revised OSHA 269 standard:

• Employers must assume default TOV values from Table V-8 or
• Conduct an engineering study to determine actual TOV magnitudes.



This change affects all transmission and distribution facilities over 69 kV, significantly impacting arc flash boundaries, personal protective equipment (PPE) requirements, and overall electrical safety strategies.

Why Engineering Analysis Matters

Utilities conducting site-specific TOV simulations can often achieve lower, more realistic MADs, helping maintain workflow efficiency without compromising safety. Key elements modeled in EMTP-RV/PSCAD include:

• System topology and line parameters
• Mutual coupling and line capacitance
• Network equivalents and boundary conditions



Such studies provide critical data that allows utilities to challenge OSHA’s default 3.5 p.u. assumptions with verifiable results.

Real-World Impact on Safety and Operations

Using conservative OSHA values, MADs can exceed 16 feet for 500 kV systems. These distances pose not only operational challenges but also risk misalignment with arc flash boundaries. Since MADs affect arc flash risk categories and PPE selection, a unified safety approach—backed by engineering simulation—is essential.

Simulation Parameters That Matter

Accurate modeling involves simulating

• SLG (Single-Line-to-Ground) faults
• DLG (Double-Line-to-Ground) faults
• Line de-energization and reclosing sequences

TOVs frequently peak during reclosing, especially if trapped charge from previous operations is not adequately dissipated.

Mitigation Options for OSHA 269 Compliance

Once simulations reveal peak TOV values, utilities can implement:

• Surge arresters strategically placed to clamp voltage
• Pre-insertion resistors to limit inrush during reclosing
• Disabling high-speed reclosing (after verifying system stability)
• Transmission upgrades as a long-term measure

Each solution must be customized to the utility’s network and verified via simulation to ensure compliance and performance.

Conclusion

To remain compliant and efficient, utilities must integrate OSHA 269 into a proactive safety strategy. Leveraging detailed TOV studies helps Keentel Engineering deliver customized, compliant, and cost-effective transmission safety solutions.

For support with simulation and compliance, explore our Power System Studies Services to see how we conduct real-world modeling for utilities.

FAQs & Answers Related to OSHA 269

Keentel Case Studies: OSHA 269 TOV Compliance in Action

Our field-tested engineering solutions have helped utilities across North America achieve OSHA 269 compliance while maintaining operational efficiency. Below are real-world examples demonstrating how Keentel Engineering addresses TOV challenges, optimizes MAD, and enhances safety protocols.

Case Study 1: 500 kV Transmission System – SLG Fault with 30-Cycle Reclose

Issue: A transient overvoltage (TOV) event peaked at 3.55 per unit (p.u.), exceeding OSHA’s threshold and inflating the minimum approach distance (MAD).

Action: Keentel disabled high-speed reclosing and performed a dynamic stability study to validate safe reclosing parameters.

Result: TOV was reduced to below 2.5 p.u., and MAD was safely restored within operational limits without compromising grid integrity.

Case Study 2: 230 kV Line – Double-Line-to-Ground (DLG) Fault

Issue: OSHA’s default MAD exceeded existing utility standards by 30%, raising safety and productivity concerns.

Action: A full EMTP-RV network model simulation was conducted, accurately capturing system behavior during fault scenarios.

Result: MAD was recalculated using a verified 2.1 p.u. TOV, enabling continued field work without capital reinvestment.

Case Study 3: Rural Utility – Surge Arrestor Optimization

Issue: Repeated switching events caused TOV spikes that breached compliance margins.

Action: Keentel installed surge arrestors at both ends of a long transmission line and ran a series of site-specific TOV simulations.

Result: TOV dropped from 3.2 p.u. to 2.0 p.u., maintaining a safe 9.2 ft MAD under OSHA guidelines.

Case Study 4: Urban Substation – Misaligned Arc Flash and TOV Analysis

Issue: An outdated arc flash study used MAD values inconsistent with TOV risk, creating potential worker exposure issues.

Action: Both arc flash boundaries and TOV simulations were updated and aligned using modern tools like PSCAD.

Result: Revised PPE requirements and MAD values ensured safety compliance and minimized operational risk.

Case Study 5: Investor-Owned Utility – Incomplete Network Modeling

Issue: A partial model failed to predict actual TOV behavior during automatic reclosing events.

Action: Keentel developed a closed-loop PSCAD model with realistic shunt conductance and network topology.

Result: Accurate modeling revealed a TOV peak of 2.42 p.u., prompting updates to work procedures and crew training.

Case Study 6: 138 kV Line – Challenging Conservative Assumptions

Issue: The default OSHA 3.5 p.u. assumption resulted in an impractical MAD that restricted field activities.

Action: A customized TOV simulation was run using detailed line and system data.

Result: The actual TOV was 1.9 p.u., reducing MAD by over 40% and aligning safety standards with realistic conditions.

See OSHA’s 29 CFR 1910.269 regulation on MAD and TOV for technical compliance guidelines.

TOV Compliance and Your Utility’s Safety Strategy

Complying with OSHA 269 requires more than paperwork—it demands engineering expertise, real-world modeling, and proactive mitigation planning. At Keentel Engineering, we help utilities:

• Reduce MAD using certified PSCAD/EMTP-RV studies
• Align arc flash boundaries and PPE strategies
• Optimize operations without compromising safety

Explore Our Power System Studies | View Substation Design Services | Learn About Our NERC Compliance Support

Ready to Optimize Your OSHA 269 Compliance Strategy?

Keentel Engineering specializes in transient overvoltage (TOV) simulations, MAD reduction, arc flash coordination, and site-specific mitigation strategies.

Explore our Engineering Services or Contact Us today to speak with our experts.