Primary falls on Secondaries...

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Pierre C Belarge

Pierre C Belarge

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Location
Westchester County, New York
I was called to a job where the EC was worried about the results of the primary, out in the street was knocked down into the secodary from a tree that fell during a storm we had the other night.

Here is what I found/saw.
1.The service disconnect is outside the building, up against the corner, no visible damage.
2. The subpanel (MLO) is inside, this is where the branch circuits are located. There is damage in the panel.
3. There has been some work that is not too old, which I was told was installed 2 years ago. As you will see from the pictures, there is a varied list of different work as well.
4. There is damage to some of the GFCIs and other loads throughout the building.
5. There is no visible damage at the weatherhead.
6. There is no visible damage at the grounding electrode conductor locations or the grounding electrode locations.


The EC prepared the house for me to megger the circuits. There were a number of circuits that failed the megger tests (.6, .8, .4, 8.9). There were a few that meggered at 189, and 201. The rest were greater than 550.

Here is my question. Take a look at the pictures that follow, and tell me how you think the damaging current flowed into the house. I am asking, not to be a smart guy, but to get some help from the collected wisdom on this site.


Typical load damage, this occurred in several locations -it is not a large house.
Crescenzo-Meg727924.jpg



Damage at the subpanel inside (MLO) - notice the different locations inside the enclosure.
Crescenzo-Meg727982.jpg



Damage at the subpanel inside (MLO)
Crescenzo-Meg727964.jpg



A closer view of the damage to the Equipment Ground Bar. - notice the damage at the EGC bar and directly across to the unground bus.
Crescenzo-Meg727984.jpg



The breakers that were plugged in at the damaged location. Notice the breakers are damaged as well as the ungrounded bus and the Equipment Ground Bar. All in the same location; check the previous picture of the whole panel.
Crescenzo-Meg727988.jpg
 
Wow.
It's weird how the arc traveled from certain circuits only.
Killed the warm floor stat even...
I'd be concerned about anything that meggerd bad.
The one thing that always puzzels me is that How do you know if a Romex wire is bad. It can megger fine and still have been blown apart like you see in the panel.
 
If you notice the white tape in two of the pictures, that is how I identified the affected circuits...not to be reinstalled until further troubleshooting.
Also, I suggested to the contractor to change the panel. He had already purchased a new panel to replace the damaged one.
 
The question I have is how do you know if something did not blow apart in the wall.
You almost need to re-do all splices.
 
Pierre C Belarge said:
What I am looking for is someone who may be able to say how they think the high voltage entered the building.

I cannot say I have provided enough information, hopefully so...
Click to expand...
looks like possibley through the EG. How well was the service bonded and grounded?
 
Growing up we had this problem a lot when cars hit poles in our area. The 12kv lines would drop down onto the 4 kv lines and triple our voltage. In our case, we had a buried transformer outside the house which would burn out after a few seconds which then blew the fuse at the pole. Until that happened, bulbs would explode, refrigerators burned out and most of the electronics would get fried. Once the transformer burned, we went dark until it got swapped out. Luckily we never had arc damage like what you show in the photos, just burned dimmers and GFIs etc. I think with arcing like that I'd worry about heat damage to the conductors, wirenuts and insulation. It seems like the brunt of the arc went from the bus to the ground bar, but I'd check the recepts. etc as well since IIRC the spacing on a 120V recept is designed to arc at about 600V so there may be some that need replacing.

Edit: In case I didn't answer your question clearly enough, I would say the voltage entered through the service. The pot on the pole isn't going to burn out right away as soon as higher voltage is fed through it, but will transform and feed that higher voltage through to the customer until it does burn out. If, in this case they had a really large difference between the two HV lines (bigger than our 4kv-12kv difference), it could be that the voltage shot up to ten times higher than normal till the pot burned, then even higher for a split second till the fuse blew.
 
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What where the exact circuits to service, looks like old one no bonding circuit to can took the hits, and of course the larger wires shown in can/picture, just wondering? !
 
Take a look at Where the feeder enters. There is arcing at the connector to the can. You have the Ground bolted to the can and yet a loose connector which is not connected to anything other than insulation and maybe touching the ground wire blew up. interesting.

on a side note. not to do with this problem. At the Warm Floor thermostat , does the Temp probe wire enter the box?
 
Sierrasparky said:
Take a look at Where the feeder enters. There is arcing at the connector to the can. You have the Ground bolted to the can and yet a loose connector which is not connected to anything other than insulation and maybe touching the ground wire blew up. interesting.

on a side note. not to do with this problem. At the Warm Floor thermostat , does the Temp probe wire enter the box?
Click to expand...

From the looks of it it seems that BX was what blew up, not the SE. It doesn't appear to have an antishort in it, so maybe the sheath cut into the insulation on the wire earlier, then the higher voltage burned it through.
 
Pierre C Belarge said:
What I am looking for is someone who may be able to say how they think the high voltage entered the building.

I cannot say I have provided enough information, hopefully so...
Click to expand...

Pierre C Belarge said:
I was called to a job where the EC was worried about the results of the primary, out in the street was knocked down into the secodary from a tree that fell during a storm we had the other night.
Click to expand...

I think you described it very well - if you are looking for a PATH?

Most likely phase to grounded, and grounded to the earth - jumpin' all over....

Since these people are lucky as it stands, as the house is still standing - I think it is time to 100% remodel that sucker. Why bother the risk of trying to save any of that?

For that matter - the whole neighborhood...
 
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Based on the pictures I'd say the high voltage ended up on the hot legs and then flashed over wherever there was a dielectric weakness. I suspect that the flash only happened on those few breakers because there was a bit more exposed copper at those screw terminals.

If it was my house I would insist on a rewire because I'd never be able to trust the original wiring again. But that's just me :)
 
makes me want to go out and buy some surge protectors!

makes me want to go out and buy some surge protectors!

I've never seen anything like that out in the field!
 
Pierre C Belarge said:
I am not disagreeing, but look at the pictures a little closer. There is no damage to the neutral. The damage is on the ungrounded and grounded conductor bus.
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I see that! I had a similiar repair job a couple three years ago, We had a high wind storm in the spring. A dead tree popped and fell onto a duplexe gable. One half of tree slapped weather head, the other half went down and trashed meter/socket. When the tree slapped the weather head, there was a snapcap insulator missing on one hot at poco termination at driploop. This bare terminal energized the neutral and sent unwanted voltage everywhere!!:mad:
 
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