Mystery Trace Burn / Lighting Controller

[DRWeig]

Fellow Power Folks,

I have a situation in which the 20-amp traces on a 277-volt lighting control board acted like fuses and blew a steel enclosure door off its hinges.

The board is simple, just thru-mounted relays with lighting rated contacts, and some logic to switch 'em. The relays survived this incident.

Upstream, four 20-A breakers tripped (covering all three phases), and upstream of that, the 400-A main feeding the lighting panelboard tripped. When the burned board was removed and replaced with a handful of wirenuts (to get the lights back on), no signs of a fault could be found and all the breakers reset just fine.

The best guess-timate I can make is that either a phase-to-phase fault happened downstream but cleared itself, or lightning came in on the load side of all this stuff. Whatever it was, enough energy was released in the burning of the PC board traces to scare the heck out of everyone.

Any comments or thoughts at all would be appreciated... I know it's scant data.

Best to ya,

Old Dave

 

[jraef]

I seriously doubt that anything from a normal supply source could create enough energy in the traces of a PC board to "blow the doors off" of anything. I would say you were hit by lightning. Otherwise, why would the main breaker trip if the downstream breakers were already tripped, or vice versa?

Here is a possibility. Lightning hit somewhere in your load, like a light fixture and traveled up the circuit to the controller. Even if the breakers opened, the energy was still coming from the load side. So the weakest link (the traces) vaporized. Once vaporized, they created a cloud of ionized metalic vapor, which facilitated a flash over to the enclosure walls. I would bet that if you look around you will find evidence of something burning through to a ground path.

"Venditori de oleum-vipera non vigere excordis populi"

 

[telasin13]

It is possible that you lost the nuetral to the board.In that case the phases would have run i series through the loads and could have caused the effect you described.

just a thought.
please post any findings.very interested in the cause

 

[buzzp]

I say it was type of surge perhaps lightning. Any faults would have remained once the wires were nutted together, assuming all breakers were turned back on.
I have designed products for industrial markets and served as a field service engineer and this is not all that uncommon. It can be very difficult to definately say the cause of such a surge but I would bet your case is lightning since everything came back up working once the bad trace was bypassed.

 

[buzzp]

I say it was type of surge perhaps lightning. Any faults would have remained once the wires were nutted together, assuming all breakers were turned back on.
I have designed products for industrial markets and served as a field service engineer and this is not all that uncommon. It can be very difficult to definately say the cause of such a surge but I would bet your case is lightning (or switiching cap banks or some utility issue) since everything came back up working once the bad trace was bypassed. Some designs have no immunity to surges others are almost bullet proof. But when it comes to lightning, all bets are off. It can do some strange things and without an intimate knowledge of the system its hard to say what can be done to increase your chances of survival next time.

 

[DRWeig]

Thanks Guys,

Your opinions mean a lot. I was further able to determine that the most-charred area was around a handful of lighting circuit conductors that all went into the same conduit, which of course makes a long run around the perimeter of the building since it's feeding a mess of lighting loads. More evidence that lightning was in the picture. I have the time, date, and location of the outage that this mess caused. I'll post you again if I'm able to find out anything from Vaisala's lightning strike database.

Best to y'all!

Old Dave