Catastrophic failure of a sub panel

[Fred B]

Have an old Murray/Arrow Hart subpanel that had a catastrophic failure arcing and burning. Fortunately I was there preparing to move several circuits for carpenters that where moving walls and was able to shut it down from the main panel before it got worse. Mason was in garage using a large wet saw for cutting bricks when I heard the arcing then saw sparks coming out of the panel.
Pre incident l had originally found evidence of heating on multiple circuit breakers as well as 100 amp feed cable and told home owner and GC of issue and after some conjoilling by me was going to be "allowed" to replace panel.

On post failure inspection of panel I found a dryer circuit wired with 10/2 that had the bare conductor landed on the ground bus not the neutral. Also found the dryer breaker had fused to the buss on one phase leg. I also found similar fusing on the 100 Amp main breaker of the same phase in sub panel as was the fused 30A breaker, (set screw welded). Heat damage on the 100A wire all the way back to main panel on that same phase.

Could have landing the gounding conductor wire on the wrong bus caused or contributed to the breaker of the dryer becoming fused to the bus of the A side of Single-Phase? (Cant separate the breaker from the bus.) As well as the previous evidence of multiple breakers showing heat damage?

I was looking for thoughts as to whether inappropriate ground/neutral landing of a 3 wire (ie 10/2) of a 240V circuit would have a direct, or indirect yet causative, effect contributing to the catastrophic failure of the subpanel over time that carried thru to the main panel 100 amp feed breaker? Or would it be a curiosity but unrelated coincidence?

 

[winnie]

My guess is unrelated, but let's walk this through.

The neutral on a dryer circuit carries current for the motor and controls, perhaps a couple of amps.

I don't see this causing much heating unless there were a loose connection.

My guess is a loose connection somewhere on a 'hot' conductor causing damage which spread to adjoining connections, eg the dryer breaker bus connection damaging the main breaker bus connection and so on.

Jon

 

[ptonsparky]

Dryer neutral to Neutral bar vs EG bar means nothing to typical breakers or their connection to the buss bars.

 

[romex jockey]

saw sparks coming out of the panel.

always ends badly Fred.....

~RJ~

 

[Hv&Lv]

Aluminum buss?
my guess without examining the panel is bad connection from stabs to buss started arcing and basically “welding” to get a good or better connection.

 

[Fred B]

My guess is unrelated, but let's walk this through.

The neutral on a dryer circuit carries current for the motor and controls, perhaps a couple of amps.

I don't see this causing much heating unless there were a loose connection.

My guess is a loose connection somewhere on a 'hot' conductor causing damage which spread to adjoining connections, eg the dryer breaker bus connection damaging the main breaker bus connection and so on.

Jon

Did find a lot of loose connections as well as cut damaged conductors (sliced along conductor). Shouldn't the breaker have tripped under such things happening, sparks and smoke? (Never did, I was able to get to the main panel and shut it down.) What is the likelihood that the main panel also has a level of damage that could compromise it? Old Westinghouse panel about very early 70's. Did find some verrrrry loose bus- breaker connections would release from bus even with cover in place while trying to turn breaker off(replacing those). But how loose is too loose? My recommendation was to replace them all, even thought replacement of whole panel would be warranted, but home owner is unwilling.

 

[ptonsparky]

Did find a lot of loose connections as well as cut damaged conductors (sliced along conductor). Shouldn't the breaker have tripped under such things happening, sparks and smoke? (Never did, I was able to get to the main panel and shut it down.) What is the likelihood that the main panel also has a level of damage that could compromise it? Old Westinghouse panel about very early 70's. Did find some verrrrry loose bus- breaker connections would release from bus even with cover in place while trying to turn breaker off(replacing those). But how loose is too loose? My recommendation was to replace them all, even thought replacement of whole panel would be warranted, but home owner is unwilling.

Do they have the proper breakers in the panel? Not that it matters now.
Did you show the damage to the owner? Any pitting on the buss means don’t use that tab.
Show him how new breakers fit in a new panel.
After that, not much you can do.

 

[Fred B]

Do they have the proper breakers in the panel? Not that it matters now.
Did you show the damage to the owner? Any pitting on the buss means don’t use that tab.
Show him how new breakers fit in a new panel.
After that, not much you can do.

It's an aluminum bus and see what looks to be a lot of oxidation on bus (white powdery looking), these loose and very loose breakers show very little contact scruff, to me indicating no spring tension of breaker onto bus, and I can't see pitting maybe because of the oxidation.

 

[Hv&Lv]

It's an aluminum bus and see what looks to be a lot of oxidation on bus (white powdery looking), these loose and very loose breakers show very little contact scruff, to me indicating no spring tension of breaker onto bus, and I can't see pitting maybe because of the oxidation.

Post 5

 

[Fred B]

Post 5

Post 6 and 8 are primarily looking to conditions found in main panel. Didn't see the level of loose breakers in subpanel as I've seen in main panel. So is it safe to assume main panel is at extreme risk to the same failure as the subpanel experienced?