Circuit Breakers 101

[Cronosin]

I ran light design and tech for my community theatre's annual one-act festival. Three weekends, 18 different one-acts spread over the 3 weekends.

Thursday before the Friday premiere on the last weekend: One of the 3 dimmer boxes (12 channels) goes belly up and says it's overloading. After killing the breaker I looked at the fuses on the box, and they were all good. Went back to the breaker, and it was hot enough to fry an egg on. Now mind you, this was a 3-breaker bonded circuit, all 100A breakers.

Within 3 hours, I had to re-patch the box to take it offline, be ready for shows tomorrow, and be prepared to talk to the electrician when he got there on Saturday.

A week later, I had to go back to the theatre since my wife was working on costume design for the next production, and I got to see the breakers they pulled. The plastic started melting. They had to move the physical slots of the breakers to 1 down from where they were in order to get it in the box. They also upped the amperage to 3-120A breakers.

The system has been fine since, as I'm teching a show there now.

 

[Chris15]

Not to be rude, but if the breakers have had enough heat through them to MELT, then shouldn't the thermals on the breakers have tripped them long before it got to this stage. Even considering the derating effect of proximity to other breakers, this obviously shouldn't have happened... You should work out why it did so that you can help to prevent it from occurring again.

 

[SHARYNF]

I would guess that what you had happen is that the buss system on the electical panel has a problem. Possibly you have a lug only panel, and so the individual breakers are not an issue, but the combined load on the panel is too high, and there is no breaker to protect it.
Typically the breaker to the load you are placing on it will not trip if the problem is up stream from the breaker, so buss problems or total panel overload can be the issue. Many times it is not easy to tell what the rating for a Main lug panel, you see 30 40 slots, and figure, hey if the number of breakers fits we are ok, I have seen these panels with 30 20 amp breakers so each leg is drawing 200 amps, also some panels have a max individual breaker size, some will not let you go above say 60 amps on an individual breaker, so it is very easy to take say a 100 amp panel and put in 200 to 300 amps worth of breakers, or place too high a load on the buss to breaker connection with the results you are describing being seen.

Sharyn

 

[Cronosin]

Thanks for the tips, and I'm glad I'm not the TD of this place. Lord knows if I was, there'd be some massive changes. The breaker box is falling apart, and we're lucky we haven't lost any other circuits, let alone anything on all the circuits.

The booth there needs the most help, and the stage's BoD is gearing up for 40th season renovations. Only problem is that they haven't mentioned any updates for the booth. What I would kill for updated control wiring and a new board...and new dimmers...and new electrical wiring.

 

[maccor]

Federal Pacific breakers are notorious for not tripping, but melting instead. Electrical inspectors (in residential construction/remodeling) here won't allow additions to be made to a FP panel. They insist on them being replaced because of the hazard. In a previous life, my business was in a leased office/warehouse space. We had 2 breakers melt/cook before we finally replaced the panel. The high school I work at now has only FP panels....a comforting thought indeed!!