I was called to residence yesterday to do an inspection of damage for the insurance company. We recently had an ice storm that took down power lines. This customer was out for 4 days. When his power came back on, he had multiple items burnt up. Micro, stove, cordless phone, dishwasher, tv, vcr, dvd player, computer surge protector, flourescent lights to name a few. The major items didn't get affected because he had them unplugged and plugged into a generator.

The odd thing about this is everthing affected was on the same phase in his (120/240) panel. Now I have seen this before on a phase to neutral short on an overhead service. But his service is all underground from the transformer pole to his house. The cause of the outage was a primary line broke a mile down the road.

Can anybody give me an explanation for this?

Did the primary break and drop onto the one line feeding into the house? Maybe it dropped onto the line at someone else's house and backfed his house.

I would consider everything you stated as "major items".
Sorry I have no decent idea as to what might have happened. Make something up (blame POCO)and be done with it.

The only thing I can think of that wasn't covered would be a loose neutral. Many of the items you mentioned are electronic or contain electronics . Electronics don't much care for high voltage. Did you take any voltage measurements while you were on site?

Were the other homes on that transformer affected?
I doubt the PoCo will do anything but it might help with the insurance company.

No that was not possible. The primary that broke was a mile down the road. And no I don't believe that it could have back feed because this is the only house on this transformer. The transformer pole is only 45' from his house. The secondary comes down the transformeer pole underground to his house.

If there were no wires down in that entire mile from the primary down to his house, that primary down will be the biggest suspect culprit. Still, it is hard to imagine it causing the surge to extend to your customer's house unless there were secondaries run the whole way (which you say is not the case).

Any overvoltage on the primary would have affected both 120 phases and everything 240. If all the damage is on one 120 phase, that sounds to me more like an arc-over in the transformer, or a fault of the other phase to neutral somewhere.

I suggest a test. Find another surge protector exactly like the one that failed. Apply 240 volts to it and see if it fails. Some will and some won't. If it does not fail, then there had to be more than 240 volts.

A closer inspection of damage to appliances might give a better idea of what the voltage involved was. Any change it might have been an UNDERvoltage issue?

Did the homeowner report any lightning events? I have experienced lightning in snow and ice storms before (but luckily was not hit by it).

My first thought when I got the phone call was an undervoltage. This seems to happen frequently in these type of storms. However upon inspection, it is all on the same phase and shows sign of an extensive surge. The next scenario is lightning. There were some thunderstorms reported in the area, however I never saw any. That is the only case that I can see but the homowner says that he didn't see any.

My next step is to talk to PoCo and have them check the transformer and connections. I am also going to recheck all secondary connections for loose neutrals, ect.

Question: Is the wire that came down the same phase as the one supplying the transformer?? If they are different phases, and the transformer primary is connected line-neutral, and say the neutral has a poor connection in it somewhere or is undersized, would it not be possible the transformer saw a momentary overvoltage if the downed wire contacted the primary neutral or the fault current tried to return through the primary neutral?? For a brief time that transformer primary would have a voltage across it somewhere between the line-neutral and line-line voltages, at least until the primary fuses opened up would it not???
I would think that would cause enough of a voltage rise in the secondary to burn things up..

A.D

So, you have no real idea as to what might have occured, but you are willing for this guys customer to lie to the PoCo.
That is called Fraud.

Why is it always the PoCo's problem?
Home-owners should have their own Surge Diversion equipment, installed in THEIR panels if they have sensitive gear that might be cooked by voltage surges.
I'm all for personal responsibility.

My first guess would be the dropped or intermittant neutral theory. The fact that all of the killed devices were on the same "phase", or leg, kinda wraps it up.

A different primary phase faulting to primary neutral would raise the primary voltage by the voltage drop on the neutral between the fault and the substation source. This could raise the voltage 10% to 30%. The worst case is if that neutral is open, making downstream line-to-neutral connection equivalent to line-to-line for a 73% voltage increase (208 volts, 294 volt peaks for the MOVs). This could certainly damage things, but not generally in ways that look like lightning damage. You would typically see burned up components, but not arc damage. Closer inspection of the damage is what could confirm or deny this kind of problem.

A simultaneous open neutral and phase cross on primary plus an open neutral and phase cross on the secondary could present the very worst case of voltage swell (416 volts, 588 volt peak for the MOVs) assuming the service transformer is not saturated.

If I were inspecting, I'd look for the kind of damage that suggests primary voltage enter the service. Start by pulling the breakers and look at the bus. Primary voltage and direct lightning strikes here could show arc damage.

I would agree. All the upstream primary voltage swell scenarios should affect both service phases the same, unless one of them was faulty.

There is such a thing as coincidence. The problems described may or may not be related to the storm or the primary power lines that were damaged a mile away. You could end up spending a considerable amount of time investigating this and never come up with a real good answer.

Trumpy makes a good point about surge protection. A robust arrestor at the service and some smaller units at the point of use has kept me out of trouble.
If you ever do find the definitive answer to this problem, please post it.

Tom

A good point, Tom.

I remember, back in the 60's, when New York had it's "Great Blackout," one of the newscasters observed that somewhere there was some kid who had stuck a fork in a toaster at the exact moment that everyone lost power ... and, to this day, secretly believes HE'S the reason for the blackout!

Well, I went back to the site today to do a follow-up. I went through the main panel at the meter and checked all connections and looked for any other signs of problem. However, no visible signs and no loose connections. I then went in the house and checked the panel in there again. (This is a rural location that has a pedestal with meter and main then splits off to house and barn.) The phase terminals on the panel in the house were a little loose but not enough that should cause problems. The neutral however was relatively tight. I was able to put a little torque on it but not much.

I then called the PoCo. I explained to them what we were facing. I got the usual, "we haven't had any problems anywhere else." So I asked them to go check their transformer and meter. I haven't heard back yet. I know they are still extremely busy trying to fix the storm damage.

Thanks for all the assistance. I will keep you all updated on anything that arises out of this.

Did you happen to check to see if the primary protector fuses in the outside telephone interface were blown or if the CATV ground block shows any sign of damaged?

Just wondering if maybe the primary power line that broke could have fallen onto the grounded bare messenger for the telephone or CATV overhead lines and caused a momentary high voltage fault between the remaining side of the transformer secondary that was still energized and the grounded neutral and/or main bonding jumper and grounding conductors.
The messenger spans are normally connected to ground at various points along the way, but maybe the initial surge was enough to cause some issues.

That’s my attempt at playing Sherlock Holmes anyway.

I guess this would only be relevent if there were two primary OH lines and a neutral on the pole crossarms.

No, I did not check any tv/telephone connections. The tv and phone were still working fine. Also, there were no overhead telephone lines in this area. All communications are buried in this area. And there is only one primary phase and neutral in the area that was down. However, directly in front of this house there are two primary phases.

It could be a complete coincidence that everything blown was on one phase. Was anything sensitive plugged into the other phase that was not impacted?

Also important, were any surge supressors plugged into the other phase? If a powerstrip on the "good" phase had activated, it would have shunted that surge to ground, protecting not only things plugged into it, but potentially everything else on that phase.

Also worth noting, if a power strip sees a high voltage spike on the ground side, it's electrically identical to a transient on the line side, and it's going to activate.

That is very possible that is what happened, Steve. I don't recall now but that power strip could have been on the other phase. If so, it might have shunted that phase. I don't think anything sensitive was plugged into the other phase. Only thing that I'm not sure about was the computer on that power strip. The strip was smoked but the computer was fine. Thanks for all the input everyone!!