Arc Flash Study on full load or worse case scenairo acceptable to OSHA standards?

[jdziegler8]

Hello,

We are doing an arc flash study for a local television station. The problem we keep running into with our partners who go out to get the data and information for all the electrical equipment and devices did not get any equipment variables such as voltage or current readings while they were out at the site testing. They want us to do this arc flash assessment based on taking 80% of the full total load at each equipment, basically going to full worse case scenario on the entire study. If I did the arc flash assessment this way, would OSHA allow this based on their NFPA 70E standards and requirements?

Example: If they have a panel rated at 100A. I will put 80A in the software as their current load readings and we run a short circuit study and load flow report based on these inputs.

 

[lielec11]

The rating of the panel in amps actually doesn't have any effect on the short circuit rating. If you run a load flow study that is different, but I don't believe OSHA has any say or specific requirements regarding load flow. For short circuit studies, you'll want your team to gather different information like voltage and short circuit rating (in kA) at each piece of equipment, and then all of the different sizes/types of feeders in the building. You will need to get wire type (copper/aluminum), size, length, conduit type, etc.

 

[wbdvt]

I will be blunt. The questions you are asking indicate that you have not done an arc flash study before and really do not have a good grasp on what is needed for a study. This is dangerous as the wrong inputs and assumptions could very well lead to personnel being under protected, thereby incurring injury or fatality.

What are your qualifications to be doing a study? Have you obtained the available fault current from the utility? Are you modeling from the utility primary protective device (most likely riser fuses), the riser cable, transformer, secondary cable to service entrance equipment? Are you calculating for equipment duty? What do you do if a protective device is overdutied? Is there a emergency generator on site? Have you read IEEE 1584? Are you aware that a new version of IEEE, IEEE 1584-2018, was released in Nov 2018 and requires that electrode configuration and enclosure size be accounted for in the new equations? There are about 40 equations now instead of 3. Are you aware that the 125kVA transformer or less and below 240V exception is gone?

OSHA only mentions arc flash specifically in 1910.269 which is for utilities. For General Industry, they require the employer to provide the proper PPE to protect from the hazard. So if there is an arc flash accident, someone is injured, OSHA will look at how the PPE was selected. So the person doing the arc flash study that determined the PPE needed, better have the qualifications, experience, knowledge in arc flash studies to prove to OSHA that the basis for the PPE selection was valid.

BTW: Load has no impact on incident energy. That is a basic fundamental understanding of what is needed or not needed for an arc flash study.

 

[MrJLH]

I would start by taking a read of NFPA 70E and IEEE 1584