Burned up 3phase service panel

[Garygood]

Looked at a panel that was burned through the front and back, all the lugs were gone the bars were burned 2/3 of the way down from were the main lugs were.
there was no load on the panel.
the main 200 amp breaker did not trip.
there was no other problems inside
the service drop did burn off the transformer at the pole.
i do not understand why the main did not trip
looking for ideas

 

[jim dungar]

Looked at a panel that was burned through the front and back, all the lugs were gone the bars were burned 2/3 of the way down from were the main lugs were.
there was no load on the panel.
the main 200 amp breaker did not trip.
there was no other problems inside
the service drop did burn off the transformer at the pole.
i do not understand why the main did not trip
looking for ideas

Maybe there was enough resistance in the arc, that the breaker saw the fault as nothing more than a load.

But you said 'main lugs were gone', and then you said the 'main breaker did not trip'. What do you have, a 6-circuit disconnect rule main panel? Was the fault on the line side of the breaker?

 

[charlie b]

I think he means that this was a MCB panel, that the incoming service conductors landed on the lugs (i.e., the ones that were destroyed in the incident), and that current passes through the lugs on its way to the main breaker. Since the incident was terminated by the damage to the service conductors at the pole, I infer that this was an arc flash event that started inside the panel upstream of the breaker. I cannot guess what started the event, but once the arc cause enough heating of the air inside the panel, the air itself was ionized and became a conductor that allowed current to flow directly from lug to lug. That would explain why the breaker did not trip.

The next question would be, what started the arc flash event?

 

[Garygood]

Burned panel

Burned panel

The circuit from the service head when through a CT cabinet, through the main breaker inclosure, into a 6x6 trough to feed the main lug breaker panel.

the lugs at the panel is where the damage happen.
so would high voltage cause the damage without enough current to trip the main breaker?

 

[Stus Dad]

arc between lugs on top of breaker

arc between lugs on top of breaker

I have seen cases where the incoming lugs shorted across to the next phase on the top of a 3 phase CB. Most of the time I could relate it to accumulation of conductive dust, or phase(s) (lug connection)overheating and burning into the next phase at the breaker. Always feels better when we really know what happened, but there are a lot of logical explanations. In my experience FWIW, it generally is a fault at the breaker or panel and not a surge coming from somewhere else.

 

[GoldDigger]

If all of the current was on the line side of the breaker, it will not be able to trip the breaker....
But it would also be possible for a sustained arc to have a low enough current that the breaker instantaneous trip would not fire.
Or the breaker was defective.

 

[flatlander]

Was there any moisture?
I have seen carbon tracking do this sort of thing.

 

[jim dungar]

The circuit from the service head when through a CT cabinet, through the main breaker inclosure, into a 6x6 trough to feed the main lug breaker panel.

the lugs at the panel is where the damage happen.
so would high voltage cause the damage without enough current to trip the main breaker?

Yeas, a high voltage is one of several issues that may have initiated the fault. A low level fault, one with lots of resistance, can burn for a long time with out being large enough to trip an upstream protective device (this is why ground fault systems are required on some 480Y/277 systems).

 

[kwired]

Looked at a panel that was burned through the front and back, all the lugs were gone the bars were burned 2/3 of the way down from were the main lugs were.
there was no load on the panel.
the main 200 amp breaker did not trip.
there was no other problems inside
the service drop did burn off the transformer at the pole.
i do not understand why the main did not trip
looking for ideas

What is the operating voltage?
What are potential contaminants the may enter the panel?
What is potential for condensation?

277/480 has a much better chance of sustaining an arc at a low enough current level that breakers do not trip then 120/240 volts does. Add a little bit of contamination and/or right amount of moisture and you have something to get the arc started.