Mike Dolt Enterprises
Mike Dolt Enterprises
User: spikes2020, Location: Nashville, TN
Asked on: Monday, April 18, 2011 at 1:38 pm EDT
Answered on: Thursday, May 23, 2024 at 6:26 pm EDT
Question: I recently did an arc flash study on one of our job sites, it was a standard 1500 kva transformer that had a normal 400A breaker coming off its buss. I was stunned when the results came back at 70 cal/cm^2. Looking at this TCC you can see that with a such a small arcing current that it took this breaker almost 50 seconds to trip.The red curve was the current settings. The blue fuse was added to protect the panel.With so many breakers and sizes all with different tripping curves is there an easier way than going though them one by one? Here i had little over 2.5 kA arcing current. Such a low current didn't trip the breaker and thus caused the huge arc flash.I am trying to select breakers from a catalog but i have to test each one's time curve to make sure it wont cause a high arc flash. Is there a better way?Any Ideas?
Understanding Arc Flash Hazards
Arc flashes occur when a significant amount of electrical current flows through a low-resistance path, creating an intense electrical arc. The energy released during an arc flash can cause burns, explosions, and even death.
Determining Arc Flash Hazard
The severity of an arc flash hazard is determined by several factors, including: Short-circuit current Arc duration Distance from the arcBreaker Selection and Arc Flash Protection
Breakers play a crucial role in mitigating arc flash hazards by interrupting the electrical current and limiting the duration of the arc. To ensure adequate arc flash protection, breakers must have the following characteristics: Adequate interrupting rating
This is the maximum amount of short-circuit current the breaker can safely interrupt.
Fast tripping curve
The breaker should trip quickly enough to minimize the arc duration.
Tools for Breaker Selection1. Arc Flash Calculator
Arc flash calculators can estimate the arc flash hazard based on the electrical system parameters, including the short-circuit current, breaker trip time, and distance from the arc. These calculators can help you identify breakers that meet the required arc flash protection level.
2. Breaker Coordination Study
A breaker coordination study analyzes the tripping characteristics of all breakers in an electrical system to ensure proper coordination and prevent cascading faults. By selecting breakers with appropriate tripping curves, you can minimize the risk of arc flashes.
3. Breaker Catalog Information
Breaker catalogs typically provide information on the interrupting rating and tripping characteristics of each breaker. You can use this information to select breakers that meet your arc flash protection requirements.
4. Contacting the Manufacturer
If you are unable to find the necessary information on the breaker catalog, you can contact the manufacturer directly. They can provide detailed tripping curves and guidance on selecting the appropriate breaker.
Additional Considerations
Arc Suppression Devices
Consider using arc suppression devices, such as arc flash relays or fuses, to further reduce arc flash energy.*
Maintenance and Testing: Regularly inspect and test breakers to ensure they are functioning correctly and meet arc flash protection requirements.By utilizing these tools and following best practices, you can select breakers that minimize the risk of arc flashes and protect workers from electrical hazards. Flag for review