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Technical Articles

Arc Flash Forum Update

Existing Overdutied Equipment

August 1, 2016

This week’s question is a continuation of last week’s topic regarding overcurrent devices that do not have an adequate interrupting rating. When the calculated short circuit current is greater than the device’s short circuit interrupting or withstand rating, the device is often referred to as “overdutied”. (X/R can play a role too but we’ll save that for another day) This week’s question: Do you/client presently have any overdutied devices? Yes No Not Sure Rather Not Say READ MORE

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PPE Selection when Interacting with non-labeled Equipment

August 1, 2016

Hi All, To put my question in context, I train Industrial Maintenance and Construction Electricians at a Community College. Some of the students are new to the field and are receiving training to gain employment. Many of the students are already employed and are taking classes to enhance their skill set. Many of these folks are involved with service work that takes them to a variety of locations from 7-11s to industrial sites. Where I am troubled is how to

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Fiber Optic Arc Flash Detection Modeling

August 1, 2016

I will start by stating that I am not 100% familiar with these types of systems [Fiber Optic Light Detecting]. In recent MV switchgear submittal the manufacturer [I assume at the recommendation of the engineer of record and or the owner] included a fiber optic light detection system for arc flash mitigation. This included “point source detection” at the terminations in addition to “linear fiber optic detection” in the breaker cubicles at the runbacks / breaker connections. In discussing with

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Arc Flash Boundary – Calculated, Larger, Something Else?

July 29, 2016

It has been a while since a question of the week was asked about the Arc Flash Boundary. This is the distance from a prospective arc flash where the incident energy is 1.2 cal/cm^2 which is the generally accepted value for the onset of a second degree burn. IEEE 1584 has a method for calculating this distance. Since electrical safety practices continue to evolve, this week’s question is about the Arc Flash Boundary. Although the AFB is required to be

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Non Specific incident energy

July 29, 2016

I have started working at a manufacturing plant where the past practice is to put <1.2 cal on their arc flash labels. The thought being that any run less than several hundred feet fed from bus duct with LPS-RK1 fuses will be less than 1.2 cals. This turns out to be true based on my calculations. Even with the maximum motor contributions the calculations hold. Does anyone consider this to be in compliance with 70E? Does anyone else do this?

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Short Circuit Calculations and Conduit Material

July 29, 2016

I recently came across a previous study that was completed for a facility that assumed a specific type of conduit [non-metallic/magnetic; PVC] vs what was actually installed [Rigid Meal Conduit], in digging into this deeper and looking at some of the short circuit calculations information available to me it appears that in the calculation they type of conduit [magnetic vs non-magnetic] can play a role in the amount of available fault current. When doing some quick simplistic calculations it appears

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