Near miss of the day .........

[VernB]

I am saying that the arc cleared itself quickly enough to not reach the trip curve of the breaker. Whether that fell within the design parameters of that breaker cannot be determined without examination.

To my field-educated eyes, the maginitude of the soot indicates that there was a small explosion, and not a (relatively) long-duration fire. I believe the arc extinguished as fast as it started, and no tripped breaker.

As for starting a fire, In my opinion, the conduit system performed its function, which is as much to protect the building and people from damage by the wiring as it is to protect the wiring itself from damage.

This building is littered (and I use the term littered as a real description) with this type of Square D panel. I don't know the designation, but they are large brown 15A bolt in breakers (I've tenatively dated them to the early 1950's). I've seen them fail to trip under even severe faults.

6-7 months ago, I had one fail right outside my office. I had a power event in the office, everything failed over to backup and I heard the transformer on the floor below thump when it reenergized. Recognizing that it was something bad enough to draw down the supply voltage to the transformer (fed from a 600A 240D entrance), I immediately went to investigate and found the stairwell full of smoke.

On investigation, I found that a circuit on one of these panels had faulted, the breaker had failed to trip, and the resultant overload had dragged the voltage down for an instant until the fault cleared itself by burning the terminals off the breaker. The arc destroyed the bus bar and burned a hole right thru the insulator sheet to the frame of the panel.

These things make me REALLY nervous, so it's my mission at the moment to make them gone :smile: .

I agree re the conduit, obviously it did what it was supposed to.

Vern

 

[LarryFine]

On investigation, I found that a circuit on one of these panels had faulted, the breaker had failed to trip, and the resultant overload had dragged the voltage down for an instant until the fault cleared itself by burning the terminals off the breaker.

Well, that fits within my explanation, mostly :

What is definite is that the current in this event did not rise fast enough and/or high enough to trip this breaker.

I am saying that the arc cleared itself quickly enough to not reach the trip curve of the breaker. Whether that fell within the design parameters of that breaker cannot be determined without examination.

It's certainly plausible that the breakers do not presently meet design specs, meaning that they're defective.

 

[480sparky]

Do they look like these?:

Square D XO breakers, haven't been made since Kennedy was in office.

 

[VernB]

Do they look like these?:

Square D XO breakers, haven't been made since Kennedy was in office.

Nope, here's a pic of a panel (still operating), if I can find a junked breaker, I'll get one of that too.

Vern

 

[mxslick]

Hi Vern:

First off, on the failures of the breakers to trip, I would not be surprised if it's because the grease on the 50+ year old mechanism is as hard as a rock. And if the breakers weren't exercised at all during thier lifetime, well, there it is.

You could try exercising the breakers a few times each, but it would probably be very risky, at the least they may not reset, at the worst they could fail violently.

If you get a hold of one of the old breakers, I would pay for you to send it to me so I can tear it down and examine it. PM me if you'd like.

 

[VernB]

Hi Vern:

First off, on the failures of the breakers to trip, I would not be surprised if it's because the grease on the 50+ year old mechanism is as hard as a rock. And if the breakers weren't exercised at all during thier lifetime, well, there it is.

You could try exercising the breakers a few times each, but it would probably be very risky, at the least they may not reset, at the worst they could fail violently.

If you get a hold of one of the old breakers, I would pay for you to send it to me so I can tear it down and examine it. PM me if you'd like.

I'd be scared to exercise the darned things. I've run across probably a dozen breakers abandoned in the panels because they couldn't be reset. I'll be gutting one of these tomorrow, I'll save a breaker for you and drop you a PM :grin: .

Vern

 

[480sparky]

I'd be scared to exercise the darned things. I've run across probably a dozen breakers abandoned in the panels because they couldn't be reset. I'll be gutting one of these tomorrow, I'll save a breaker for you and drop you a PM :grin: .

Vern

Post us a pix before you ship it out!

 

[jim dungar]

These are probably the older Square D type A1B breaker which were built from 1934-1948. I don't think they are the ML-1 style (which I think were black).

If you can post a picture of the panel namplate as well as one of the busbars.

 

[VernB]

Ok guys, here's the pics of the unidentified panelboard, breakers, and busbars. Inquiring minds want to know .

Note that this is a 225A rated Square D panelboard and it's configured for 3 wire 240D 3 phase in and 2 wire 240V single phase out (all 2 pole breakers). I've also seen them here as well configured for 240/120.

Vern

 

[chris kennedy]

since Kennedy was in office.

I try to stay out of the office.

 

[480sparky]

One photo provided the clincher. Hint: it's the one with 992215 on the side.

It's a Square D 992215 breaker.

http://www.relectric.com/Store/Circuit-Breakers/992215?ppcs=m&rid=254191