This week's question is about the results of incident energy calculations exceeding the 40 cal/cm2 threshold that many use.

For most, the answer will be an approximation at best, especially if you are involved with arc flash studies at multiple facilities such as a consultant or corporate position.

The question refers to the value listed on the arc flash label and is used to define the arc flash protection requirements.

The question is:

On average, what percentage of equipment locations have a calculated incident energy above 40 cal/cm^2?

0 to 10 percent
11 to 20 percent
21 to 30 percent
above 30 percent
Doesn't apply to me

I have about 2500 buses. Not practical to talk about "locations". About 25% are above "40 cal/cm^2" running the data raw out of SKM but this is not really accurate. Many of them are buses that are not accessible for work (so don't count) and many of them are where SKM defaults to Lee calculations because many of my busses are outside of 300-15 kV.

We have between 30-40% of our locations across the system that have 40cal or higher energy. Our company has taken the stand that this is too high of a risk to our employees. We ar eworking on lowering those energies to 25cal or lower. with 138 stations across our system this is a huge task that involves many people.
Thanks!

The question can be answered a couple of ways, either by the number of plants or the number of buses within a plant. We have hundreds of studies we have done but never kept statistical data, in general I would answer it this way:
approximately 75% of the plants we do studies for have 40cal+, of those somewhere between 5% and 15% of the buses are 40+.

We were just talking about that this morning. I have exactly one switchgear breaker at 40 cal/cm2, and nothing higher.

We've done studies in many locations and most of the larger facilities exceed 40 calories -at the Utility and at the meter and connected service. Once past that point, we rarely find locations exceeding 40 calories, that is unless it's a location with a large step down transformer with over current protection (on the secondary) that's very near or at the highest acceptable level. Even then, those rarely exceed 40 calories because of the 2 second rule.

We ar eworking on lowering those energies to 25cal or lower. with 138 stations across our system this is a huge task that involves many people.
Thanks!