Arching Causes Main Breaker To Trip?

[Mark Sylvester]

At my morning inspection yesterday I was inspecting the kitchen sink area when POOF there was an arch that came out of a junction box located within the sink cabinet that was for the GD.

Now heres my question. Not only did the breaker trip for this circuit but the Main also tripped. There where two main disconnects one at the panel and one out at the meter. The one at the meter is the one that tripped while the main at the panel did not.

What are your thoughts on what would cause this?

And yes I am calling for a complete review of the electrical components.

This was a 60's SFH.

[Paul W. Abernathy]

Anytime a main breaker trips...have it evaluated. This is a good example of an issue where if this was in a industrial environement we would not have cordination....and could have lead to even larger issues.

Anyway I digress......yes, have it evaluated...even if you did not state the make and models of equipment you are dealing with I would say again anytime a main fuse or breaker blows.....have it evaluated...simply not worth playing the odds on someones life that could be living in the dwelling.

[Greg Fretwell]

I am guessing that the branch circuit breaker was just a little sluggish and the main took over clearing a bolted fault. A lot would depend on what the total load was at the time. If the A/C or some other big load was starting at the same time you might have had plenty of current available.
You certainly need to have the short under the sink fixed.
Was this a stab lock?

[Mark Sylvester]

No the panel was a newer SD panel.
There also was a surge protector installed on two of the circuits that was wired improperly.

Should have seen me fly out from under the cabinet when the sparks started flying.

[Paul W. Abernathy]

Mark,

Recommend they have it addressed and have the electrician give the panels the once over........

[Mark Sylvester]

Oh for sure!

I'm just trying to figure out what would cause this to happen. Why would the main at the panel not trip but the exterior main would?

[Paul W. Abernathy]

Mark,

As greg stated..it could simply be an issue of a lower threshold on the breaker when dealing with cordination.

Now if their was a load on the system lets say during the actual fault you witnessed under the counter......the main breaker outside just might have detected it.....speculation is the worse enemy of this because without seeing it, touching it and testing it we can only speculate...

Maybe their was a fault ahead of the remote distribution panel that was happening at the same time as the fault you witnessed...who knows as you know thats why we educators of AC/DC Theory call it AC/DC Theory....much of electricity is known and much is still unknown.....we are still learning everyday about electron flow and so on......how the protons and neutrons react and well you got the picture.

In this case.......very hard to speculate but chances are as greg stated...a bolted fault took place....maybe improper wiring of the remote distribution panel aided in it........but the main thing is having it looked at...

In my 20+ years I have only been on a select few calls of a main breaker tripping....so when we got to these issues we treat them very serious because the individual OCPD's should function well before the main OCPD functions.......

[Mark Sylvester]

I hear you.

Hope your feeling better.

[Paul Dickerson]

I was installing insulation with my brother once when he accidentally punched a staple through a romex cable. The staple shorted between the hot and ground wires. The 20 amp branch circuit breaker did not trip, but the 125 amp main breaker did, and almost instantly. This was a 70's vintage Murray panel I believe. I would not have guessed you could stuff that much current through a staple. I am not sure how much current is required to open a 125 amp breaker so quickly, but I imagine it must be in the 200-300 amp range.

[Marc Benz]

Originally Posted by pdickerson

I was installing insulation with my brother once when he accidentally punched a staple through a romex cable. The staple shorted between the hot and ground wires. The 20 amp branch circuit breaker did not trip, but the 125 amp main breaker did, and almost instantly. This was a 70's vintage Murray panel I believe. I would not have guessed you could stuff that much current through a staple. I am not sure how much current is required to open a 125 amp breaker so quickly, but I imagine it must be in the 200-300 amp range.

Paul ,

typically with direct short the breaker will trip useally over 8-12 X of the breaker rating stamped on the handle i will give you a quick example

the SqD QO and HOM series breker 15 and 20 amp with good short cirucit they will trip at about 200 amp but keep in your mind it pretty much what the POCO supply set up

but for most breaker overload is not too bad but short circuit it kinda a race for which breaker will trip either branch breaker or main breaker will trip IMO most case useally both will trip at the same time due the mangatic charcatics inside of the breaker [ i will find a chart compared the 20 amp single pole breaker vs 200 amp main breaker tripping time chart kinda instering to see how it work ]

Merci, Marc

[Frank P. Newman]

Virtually all circuit breakers have a tripping 'curve' rather than one specific trip 'point'. In large industrial systems the breakers (and/or the relays activating them) are normally coordinated so that the curves don't overlap, allowing the breaker closest to the load to trip first. In residential applications, any sort of coordination between breakers is accidental at best, so it is possible (although not common) that a fault of some specific magnitude can trip both at almost the same time.

In this case the main in the panel is the same brand and vintage so probably coordinates ok with the branch circuit breaker while the main outside may be a completely different brand with completely different characteristics. Another possibility is that the 'outside' main is defective.