interesting troubleshoot

[stew]

Got to a customer last nite and the complaint was that there was a J box that was"glowing". This was at a local bar in the U district so I wasnt sure if the students had had a bit too much or what. Lo and behold they were correct. Both cover plate screws were glowing red. When I remarked to the customer that it appeared that there were some gounded conductors in the box he said well why didnt the circuit breaker trip then? That puzzled me as well as he led me way back to the main panel and viola! a 400 amp 42 space you guessed it FEDERAL PACIFIC dinosaur with all breakers neatly still latched. As this panel cover was not marked very well we located the circuit in question by trial and error (prior to touching anything) by swithching off individual circuits until the red glow stopped. Repaired a melted mess in the box with 2 reds completly gone and most of the spring on the neutral red burned away. nasty mess to say the least. Cost the customer a good bit to fix but heck of a lot less than a fire. Of course we now will probably get the panel replacement as well as the customer now knows he owns a never trip federal pacific panel.

 

[templdl]

Re: interesting troubleshoot

Remember that a CB most see enough current for enough time for it to trip. The thermal element is inverse time current. As a bench mark NEMA AB4 field testing require that breakers 250v and less and up to 30at must trip in 50 seconds or less at 300% of the breaker rating. The instantaneous, magnetic, trip element is commonly 7-10x the breaker rating. The question is what was the actual current? You may not want to condemn the breaker just yet.
When you think about it a 20a breaker at 120v can supply 2400w of heat and can supply 7200w for 50sec before tripping. Please not that the thermal trip curve in i2t, inverse time current so an overload of 200% would take much longer.

 

[rattus]

Re: interesting troubleshoot

Were these breakers always defective or did they not age gracefully?

 

[iwire]

Re: interesting troubleshoot

Originally posted by rattus:
Were these breakers always defective or did they not age gracefully?

More links about this then anyone can ever need.

FPE Links

[ September 14, 2005, 10:14 PM: Message edited by: iwire ]

 

[steve66]

Re: interesting troubleshoot

A jbox is glowing red, and it sounds like everyone is just sitting around saying "Hey, look at that!!" while waiting for the electrician to arrive. No one thought to switch off the power while waiting for an electrician to arrive.

If a fire started, they probably would have just sat there saying "Hey, look at that!!" while waiting for the fire dept. to arrive.

Sorry for the rant, but I think it just shows how naive a lot of customers are about electricity.

Steve

 

[petersonra]

Re: interesting troubleshoot

It's a bar. people who have nothing better to do than hang out in a bar are not likely to be bright enough to figure out that turning off the power is the thing to do.

The bar owner probably figured if the red glow mesmerized them, they would drink more. I am almost surprised he fixed it at all.

 

[stew]

Re: interesting troubleshoot

and the instananeous current that a short to ground which was the case here as it arced many times against the box would have tripped any other breaker besides a . Beside which I would condemn the breaker regardless. ITS A FEDERAL PACIFIC !

 

[iwire]

Re: interesting troubleshoot

Stew there is no way to tell if you had a bolted fault, circuit impedance can prevent any breaker from opening.

All that aside I am also no fan of FPE, hopefully you do get the panel change out of this.

 

[benaround]

Re: interesting troubleshoot

Stew,

So, did you find out what the problem is? The only time I've seen things glow red is when the wiring method was "BX" cable.

 

[templdl]

Re: interesting troubleshoot

What's interesting about these replies is that many assume that the breaker should have tripped. One must be reminded that a breaker must see current of a high enough magnitude and a length of time to cause it to trip. Please note that there must have been a high resistance fault present that would have caused enough heating but yet limit current. Unless that FPE breaker is tested one can not conclude that it wouldn't have done it's job if the time/current met its tripping requirements. I am in NO WAY defending the FPE product. I agree that the FPE product doesn't have a good reputation and certainly is a product that I would recommend to be replaced. But it is entirely possible for a QO, CH, BR, GE, Siemens, etc. breaker not to trip under the exact same circumstances.

 

[steve66]

Re: interesting troubleshoot

The bar owner probably figured if the red glow mesmerized them, they would drink more. I am almost surprised he fixed it at all.

LOL

Its also great for warming you hands during those cold winters.

 

[BruceH]

Re: interesting troubleshoot

Just a side note. I just installed a Square D QO panel in place of an old Murray (I believe) and discovered a short that would instantly trip the branch cb of the QO. Turns out this short had probably been there for years and never tripped the breaker of the old panel. The short was in the switch box of their living room. They were thrilled after seeing for themselves how sensitive their new QO was, I'm sure now they understand why I insisted on top quality materials.

 

[iwire]

Re: interesting troubleshoot

Bruce is it possible you connected a floating grounding conductor during the course of your work?


It seems very unlikely a short circuit that immediately trips the QO but did not trip the Murray at all would not have started a fire long before you got there.

 

[BruceH]

Re: interesting troubleshoot

Yes iwire, I guess that is possible. I did find some loose connections in the old panel and I did find a short in that switch box as well. Nevertheless, it was a hazard but it is corrected now.

 

[templdl]

Re: interesting troubleshoot

I agree with iwire as any type of shorted conductor is going to generate heating to some extent depending upon the severity of the fault.
I may be noted that the QO has a lower instantaneous trip calibration than the Murray which is SqD's standard. It's interesting to note the evolution of magnetic trip calibrations as it used to be common for them to be 10x and even more of the breaker rating. It was just how they had designed breakers. Then some manufacturers reduced the mag. cal. to about 6-7x and called them low magnetic while SqD appeared to standardize on the lower cal. and the had an optional high mag which was about 10x+. There is no standard that I'm aware of for magnetic trip calibration other than to protect the breaker and keep it within its withstand, that is to clear the fault before the breaker can be damaged and fail the UL489 test procedure.
Also, for cost saving miniature beakers are commonly manufactured in families where breakers with ratings 15-30a may be may of the same parts and their mag calibrations the same, 31-70a and 71-100a would be other families.
But in all reality getting that maag rating down is more likely to sense and clear a fault much quicker