RumRunner
Senior Member
- Location
- SCV Ca, USA
- Occupation
- Retired EE
The pictures show the arcing was primarily at the sharpest points or corners on the busbar, and also on the corners of the attached peg for mounting a breaker. Such corners would be where the electric field gradient across open air would be the highest (in other words, where the electric field is changing the most quickly vs. distance). The arcing evidently occurred across an air gap, which is different from arc tracking across an insulator caused by surface contamination or moisture. I could be wrong, but I don't think 480V L-L would normally be sufficient to induce corona and initiate arcing across significant air gaps like that causing the damage in the photos. However, the 480V could likely sustain the arcing once started. For the OP, do you know the approximate distance between the points where the arcing occurred?
I wonder if there could be voltage spikes occurring from the switching of PF correction capacitors, a defective transformer, or something else. Perhaps a surge arrester could be installed on the panel, preferably to clamp significant voltage surges, but also to confirm that a large surge had occurred if the arrester itself was also damaged.
I agree.
480v is not high enough to manifest Corona. The first incident could have developed slowly that no one noticed or simply ignored until the meltdown.
Most "guesses" on how this happened could have merit--from snakes to rats to dust.
However, the decision to replace the burnt busbar (prior to this second incident) and not the entire panel was a hardknocks remedy. Band aid in other words.
The melted busbar evidence is telling that high temperature caused this meltdown.
The arcing that occured inside the panel had raised the temperature so high, the ionized air formed a plasma that the surrounding material turned to carbon--the by-product of combustion.
Carbon is conductive.
The insulating property of composite material even ceramic had developed a bridge where carbon created a path to ground. This carbon is visible on that photo.
The sustained arcing that turned the enclosed ionized air into high temperature plasma could have compromised other insulation like thermoplastic covering for conductors.
I agree with Sahib that meggering the conductors to check the insulating properties of the conductors even after replacing the entire MCC.