Primary falls on Secondaries...

[guschash]

Pierre what was your method of meggering the Panel?

 

[mivey]

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.

Looks like to me it came in (or left) on the neutral and went to the can and who knows where else. Reference the smoked neutral/can/locknut at panel entry.

Once on the can, it seemed to find certain circuits through the Gnd/Neu busses. Maybe the little bare "antennas" sticking through the bus getting closer to the overly-stripped-back hot wires going into the breakers?

My guess anyway.

You expect trauma in areas of discontinuity (turns, deadends, connections) and you can see that in some areas, but not all. I have seen lightning blow out some receptacles and skip others.

Nice pics.

 

[cowboyjwc]

I had the same thing happen awhile back. One house had the meter blown out of the socket, but only one GFCI ruined. The house behind it had a new service and they lost all of the equipment that was grounded to the panel cover (cable box, cordless phone) and they had some emt run and every j-hook had an arc mark. They also discovered that the phone lines on the poles had melted. Now there were 4 houses all fed from the same transformer and the primaries landed on the ground wire, but only two house were affected. When I asked the POCO why that would happen his best answer was, "it's electricity it does what it want's".

 

[Sierrasparky]

I had the same thing happen awhile back. One house had the meter blown out of the socket, but only one GFCI ruined. The house behind it had a new service and they lost all of the equipment that was grounded to the panel cover (cable box, cordless phone) and they had some emt run and every j-hook had an arc mark. They also discovered that the phone lines on the poles had melted. Now there were 4 houses all fed from the same transformer and the primaries landed on the ground wire, but only two house were affected. When I asked the POCO why that would happen his best answer was, "it's electricity it does what it want's".

did those home get re-wired? How can you tell the damage in the wall?

 

[bobsherwood]

My bet.... The medium voltage hit the service drop GC. In an instant, from there to every neutral in the house and through the load, back to the breakers. I would bet the damaged breakers had the bigger loads?

 

[cowboyjwc]

did those home get re-wired? How can you tell the damage in the wall?

Not from what I could gather. My boss kept telling me that I needed to inspect it and tell them if they were safe or not and I kept trying to explain that they needed to get someone in there and megger out the houses and then I could tell if they were safe or not.

I think the POCO actually took care of everything and had it done. I don't inspect a lot of residential, but when it goes boom they call me and then the combo guys take over.:smile:

the really interesting part, and you can kind of see it in Pierre's pictures, is what went poof and what didn't.

 

[Jim W in Tampa]

Really don't see it mattering as to how it entered . 600 volt insulation was subject to thousands and broke down. Insurance company lucky was no fire. If i owned this house i would demand a complete rewire and all appliances replaced or sell the insurance company the building. Unlike a typical fire job the damage here is not isolated to any area.
I was trained when doing estimates on fire damage to cover our behind . You won't be able to go back for more money after settlement. Really would not want this house back even after its fixed and it will be a devalued house for ever.

Whats up with green romex ? something new ?

 

[macmikeman]

Pierre, you said in early posts that the gec and grounding electrodes looked fine. Is there a possibility that they served no function at all during the event, and the neutral of the house system and utility drop served as the primary current path during the event?

 

[220/221]

I have seen this situation twice in my career. Unfortunately it was before I took pics of everything I encountered.

The first time, a sub of ours was drilling 24" holes, 6 feet deep for parking lot lights in a 200 unit, occupied apt complex. There was the loud thump, the breaker tripped and automatically reset a few seconds later and thumped again. It blew up the auger and sent the HV thru the system.

The high voltage seemed to show at the grounds much like yours did but not as often. There were tons of TV's and appliances plugged in but relatively little damage. The ground wire on the washer pigtails were blown out in about 5 units. I remember a zip strip melted to the carpet. We were troubleshooting there for a while, fixing things as they came up.

A few years later some OH high lines came down onto the secondarys a mile or so away from the service call I went to. Again there was a lot of damage at ground point's. I remember a meyers hub on a 600A service being half melted off. Your pic of the 1" locknet reminded me ot that.

I think the HV went thru the grounded conductor and spread out, jumping over and arcing at weak points that appear random.

 

[SEO]

Pierre I agree with the others that the primary entered the house on the grounded conductor. How long was the primary voltage connected to the homes electrical system? I think that it will take a lot of investigation and they may have to open some walls. By the way very nice pictures!

 

[Sierrasparky]

Pierre
Are they going to rewire this house.
As many have stated and I agree that you cannot certifiy what you cannot see. I have taken megger readings to a visibly damaged conductor that measured ok. I don't see how you can verify the condition of the wires in the walls

 

[benaround]

The HV came in on the grounded conductor and like all electricity was seeking it's source,

I'm just guessing here, but maybe it jumped from the grounded conductor to the GEC thru

the earth and back to the source via the multi-ground HV system ?

 

[Pierre C Belarge]

The HV came in on the grounded conductor and like all electricity was seeking it's source,

I'm just guessing here, but maybe it jumped from the grounded conductor to the GEC thru

the earth and back to the source via the multi-ground HV system ?

That is an interesting comment. When one thinks about where the source may actually be. I am not sure where the source is, this house is tuckes away in a very quiet street that most people would say is in the woods. It is miles from any actual town location.
I am guessing its actual source is miles away.
You have brought up a good point, and I agree with it.

 

[nakulak]

I find these types of incidents interesting. When I upgraded my own resi service I put a fused disco outside, even though I have a main breaker panel, just for kicks. I've often wondered if putting a 3 phase disco and fusing the incoming neutral would provide more protection from accidents like this ?

 

[Pierre C Belarge]

Are the owners going to rewire the house? I cannot answer that question, I am not in control of the job.

Note:
The homeowners were on vacation when this happened. When they got home, the street repairs by the utility company and the tree removal (actually 3 very large trees) was complete.
The utility company turned the power back on to all of the houses (not many in this area, but the primary came down, so who knows how many houses were affected), and the homeowners had power on until the day I was there for the testing. I told them not to restore power after my testing until the corrections were effected, but I have not authority on this job, I am just a consultant for the EC.
I would take an educated guess that 75% of the house was recently updated with wiring and a new service (2 years ago).

I did not megger the panel, I meggered the branch circuits and the SER/SE service cables. I used the Fluke model 1587.
I meggered hot-grd; hot-hot; hot-neutral.
I checked (as I always do) to see that the contractor did not miss disconnecting any of the loads. He missed a couple of lamps in hihats and then we started.


Someone mentioned that the SER in the panel did not fault, but the cable next to it. That is correct, the SER was scorched, yet not damaged.

I am tending to agree that the utility fault came in on the grounded/neutral conductor went through some loads, and found a way back out through the grounding electrode system.

Why some circuits are not affected always baffles me. Someone mentioned the circuits affected may be the ones with larger loads...that is an interesting concept.

Thanks for all of the help!!!

 

[Pierre C Belarge]

I find these types of incidents interesting. When I upgraded my own resi service I put a fused disco outside, even though I have a main breaker panel, just for kicks. I've often wondered if putting a 3 phase disco and fusing the incoming neutral would provide more protection from accidents like this ?

As you can see from the picture, the panel inside of the house is MLO, there is fused disconnect outside. It looked as new and undamaged as the day it was installed. I was very surprised not to see any damage there. The overcurrent protection in the service disconnect did not open. Go figure.

 

[hillbilly]

My bet.... The medium voltage hit the service drop GC. In an instant, from there to every neutral in the house and through the load, back to the breakers. I would bet the damaged breakers had the bigger loads?

That's my thought too.

steve

 

[Sierrasparky]

So other homes were afected and the POCO turned on the power?
WOW.
All that carbon on the parts could start a fire. I've seen stuff like that flash over.

 

[SEO]

As you can see from the picture, the panel inside of the house is MLO, there is fused disconnect outside. It looked as new and undamaged as the day it was installed. I was very surprised not to see any damage there. The overcurrent protection in the service disconnect did not open. Go figure.

I'm not surprised to see that the fused disconnect did not open and the exterior equipment looked good. If the fault entered the system on the grounded conductor it by-passed the overcurrent device and went straight to ground searching for any and all paths back to its source. The ground rods at the first disconnect would have relieved some the water pipes if bonded to system would have taken voltage and the equipment at the end of the fault taken the rest. The first contractor that I worked for always said that the house at the end of the line would take the most damage when the line was struck with lightning. I think the same holds true in this case, the end of the line equipment took the most abuse.

 

[Pierre C Belarge]

The only grounding electrode is the rods, the well has plastic pipe entering the house. The grounding electrode system is all terminated in the outside service disco (new service 2 years ago).