Meters and Incident Energy

THIS IS FOR INFORMATION ONLY - DO NOT BASE STUDIES ON THIS DATA - IT IS JUST ONE COMPANY'S TESTS!! (<<had to put the legal thing in here)

Hi Everyone,
There has been quite a bit of discussion and debate about what to do when working around meter bases. At one of the IEEE 1584 meetings, a presentation was made about arc flash testing on 480 V meters.

The problem is there is usually no protection directly upstream from the meter. Using IEEE 1584 formulas you can get some pretty huge incident energy numbers.

One of the committee members that works for a large electric utility questioned the large numbers from the calculations. The thought was they don't have much data to support lots of people being injured or killed while working on meters when an arc flash occurs.

They decided to conduct their own testing and here is what they learned (again take note of the legal thing at the top - this is just FYI info)

They tested both self contained meters and transformer (CT) rated meters at 4 different fault current levels.

6.6 kA
12.7 kA
25.7 kA
44 kA

480 Volts
18 inch working distance (where calorimeters were located)

The results were surprising.

Self Contained Meters:

10 tests at each current level for a total of 40 tests.
Maximum measured incident energy was 21.1 cal/cm2
Each test was above 4 cal / cm2
15 were above 8 cal/cm2 (less than half of the 40 tests)

CT Rated Meters

46 total tests.

Max measured incident energy was 10.7 cal/cm2
All but one was BELOW 4 cal/cm2

The duration was the big thing. The arc extinguished usually due to the bus vaporizing. Higher current often produced faster extinction (quicker vaporizing of conductors)

What does all this tell us?

IMHO - great info but we still have a lot more to learn.