Almost an event

[augie47]

How close can you get to a "boom".. One of several Service disconnects at older industrial facility

 

[LarryFine]

Now, that's what an overheated terminal looks like!

 

[ptonsparky]

I do like the increasing age of the fuses left to right. Somebody was right on top of the issue.:happysad:

That’s one where you go O! S!, after you throw the switch and open the door.

 

[electrofelon]

I assume we are supposed to be looking at the bare conductor and that it is not a corner grounded system?

 

[mopowr steve]

Oooooh-Baby
is my reaction

 

[Dennis Alwon]

It's amazing that the conductor is still isolated from any conductive material.

 

[LarryFine]

Years ago, we were called on a troubleshoot for loss of power to an entire basement apartment (2 bedrooms, one bath, one living room, but no kitchen). I traced the power to an upstairs receptacle; the entire basement wiring had been wired onto this one existing circuit!

I noticed that the incoming conductors were bare(!) aluminum and loose on the receptacle terminals. I opened the wall above the box to expose the bare wires, and here's what I found:

All three conductors were completely bare for about two feet, perfectly parallel as if still in the cable, pristine and shiny, and there was no trace of ash or burned plastic. It was as if the sheath and conductor insulation had evaporated and left rounded edges where it ended.

 

[ggunn]

I assume we are supposed to be looking at the bare conductor and that it is not a corner grounded system?

Assuming you are not joking, I believe we are supposed to be looking at the area of contact (or the lack of it) between the bottom contacts of the disco. The bare conductor is likely that way because of it.

 

[LarryFine]

Assuming you are not joking, I believe we are supposed to be looking at the area of contact (or the lack of it) between the bottom contacts of the disco. The bare conductor is likely that way because of it.

That's the upper left, incoming L1.

 

[ptonsparky]

The picture is rotated to the left on my phone. I would call it top left of the disco

 

[MTW]

This one went BOOM...

This one went BOOM...

At 480V it would have gone boom much sooner.
This one was dirty with grinding dust, and the condensation sent it over the edge.
You can tell by the amount of metal vaporized, that it was connected as a service disconnect.


MTW Ω

 

[ggunn]

That's the upper left, incoming L1.

The way the picture is oriented when I see it there are three disco blades on a vertical bar. The bottom two blades appear to have rotated on the shaft they are attached to so that when the top blade is fully engaged, the middle one has a somewhat reduced area of contact and the bottom one has a drastically reduced area, and the conductor connected to the bottom one has gotten so hot that the insulation has been burned off.

 

[LarryFine]

The way the picture is oriented when I see it there are three disco blades on a vertical bar. The bottom two blades appear to have rotated on the shaft they are attached to so that when the top blade is fully engaged, the middle one has a somewhat reduced area of contact and the bottom one has a drastically reduced area, and the conductor connected to the bottom one has gotten so hot that the insulation has been burned off.

The pic is rotated. Allow me:

 

[ggunn]

The pic is rotated. Allow me:


View attachment 23219

All righty, then. Substitute "left" for "bottom" in all I wrote.

 

[kwired]

If raceway is non metallic, it may never go boom.

 

[Jraef]

The way the picture is oriented when I see it there are three disco blades on a vertical bar. The bottom two blades appear to have rotated on the shaft they are attached to so that when the top blade is fully engaged, the middle one has a somewhat reduced area of contact and the bottom one has a drastically reduced area, and the conductor connected to the bottom one has gotten so hot that the insulation has been burned off.

That’s similar to what I was thinking. But I looked at it as the other two poles were opening, but the phase C pole was not, and it was a corner grounded system so current kept trying to flow in phase A because of some load situation, burning that blade. But on second thought, there wouldn’t (shouldn’t) be a fuse on that corner ground, and it would/should be B phase, not A. So your scenario makes a lot more sense.

Odd though that there is not more heat damage to the other conductor insulation given that the A phase completely burned away. Not even ashes left?

 

[kwired]

That’s similar to what I was thinking. But I looked at it as the other two poles were opening, but the phase C pole was not, and it was a corner grounded system so current kept trying to flow in phase A because of some load situation, burning that blade. But on second thought, there wouldn’t (shouldn’t) be a fuse on that corner ground, and it would/should be B phase, not A. So your scenario makes a lot more sense.

Odd though that there is not more heat damage to the other conductor insulation given that the A phase completely burned away. Not even ashes left?

Good chance that insulation cracked and then flaked away? Pretty sure I have seen that before with XLPE insulation types. THHN melts and drips away if it stays hot for long enough.

 

[LarryFine]

Odd though that there is not more heat damage to the other conductor insulation given that the A phase completely burned away. Not even ashes left?

Read post #7.

 

[S'mise]

I am guessing it was a maintenance man that replaced the fuse(s).

What self respecting Electrician would replace that fuse without first lookig over the disconnect?

My eyes always go to the top of the disconnect to verify all fingers have physically separated on the phases and the wiring looks ok.

I'm glad there was no boom.