Ok. I'm investigating an arc flash accident.
In the above image. The breakers encountered a first short which deposited carbon into the plastic enclosure and lugs. During a second event. The electrician just touch the right most live terminal into the right most lugs. It suddenly arc flashed causing the damage as well as hurting his arms.
What I want to know is. If there is merely carbon deposited in the breakers. Is it enough to cause arc flash between the two live terminals. It's like the carbon initiated the arc flash?
The transformers is an open delta 3 phase composing of two 75kVA transformers serving 240volts to an office building (the red and black line). It's connected directly by short wires to the service meter and directly the breakers. When the arc flash occurred, there was no overcurrent devices upstream of it. The transformer breaker didn't trip.
Just tell me if mere carbon deposit in the breakers can initiate arc flash. Notice the middle plastic is not damaged. It's as if the arc flash jumped in front of it between the terminals, is this possible? Note the smaller wire is not connected to the right most live wire. The smaller wire is just the ground hidden at the back of the live wire.
To clarify my questions. What I was asking was supposed just for sake of discussion the drop thing is not a tool but a thin layer of carbon (again just for sake of discussion or better yet let's say the switch gear or whole facility is turn off and you put a thin layer of carbon between the conductors ). Since a thin layer of carbon is a conductor.. and this bridges the gaps between the two terminals or huge wires with large incident energy, would this initiate an arc flash or should the thing drop be a tool that can pass through huge current? Or can a thin layer of carbon enough to cause chain reaction (or negative resistance) effect that would build up the arc plasma from miniscule until the textbook arc flash occurs that throw the person across the room?
In panels or switchgears where a tool dropped can initiate a major arc flash. I'd like to understand the behavior if carbonized particles (say from previous short) get into the conductors causing a short. What quantity before they can initiate and chain react into a major arc flash?
Imagine there is little amount of carbonized particles between the two phases or conductors. Once it conducts. It can vaporize immediately. Would this be enough to establish a major arc flash. What is the carbon deposit threshold before this can occur?