One thing people take for granted is the incident energy levels posted on the arc flash labels in their facilities. Once the study is complete most people never give it another thought and just assume that the numbers are correct. I'm not saying you need to go around second guessing the engineer who did the calculations, but what I am saying is that over time these numbers are in jeopardy if the equipment is not maintained in a satisfactory manner.
Without the proper maintenance being done on the equipment incident energy levels can go from relatively low to extremely high and there would be no way to tell until it was too late.
The factors of an arc flash
There are three major inputs required for an arc flash calculation, current, distance, and time. Time is the only one of these which is determined by the protective equipment operating the way it should and more importantly at the speed it should. Circuit breakers, protective relays, and fuses make up the majority of equipment you want to pay special attention to but in this article I'm going to focus on circuit breakers.
What is a circuit breaker?
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by an overload or fault condition. They are also one of the key pieces of equipment that are protecting an electrician working downstream on the circuit.
Why is circuit breaker maintenance so important?
Circuit breakers are a mechanical device, so inherently they have parts and pieces that are required to move in order for a successful operation. When calculating incident energy levels, the engineer would typically use information from the manufacturer with regards to how quickly those parts and pieces work together to complete the operation and interrupt the circuit.
If the required periodic maintenance is neglected then the operating times provided by the manufacturer become irrelevant. Circuit breaker parts and pieces will start to malfunction (contacts can start to stick and springs might lose their strength) and even worse not work at all. It might not seem like much but it only takes milliseconds for the incident energy on a typical 600-volt motor starter to go from negligible to deadly.
Here is an example
Check out this chart of a typical 600-volt motor starter bucket arc flash:
Along the bottom is time, starting at 0.01 seconds and going to 2 seconds....that's right, only 2 seconds. See how quickly the incident energy rises! Between 0.2 seconds and 0.5 seconds, the incident energy reaches almost 20 cal/cm2 (that's really high).
Using everything we just went over, picture what happens to your arc flash levels if the circuit breaker maintenance hasn't been done in 3 years, or 5 years, or worse 10+ years! Chances are high that the operating speeds of the mechanical parts in your breakers are significantly slower and it takes only fractions of a second and you are in serious trouble.
I hope you found this article useful and if you did please share it using the social media buttons at the bottom of the post! Also if you would like some help with your electrical safety program, feel free to contact me anytime.