What could have caused this damage?

[anderson100]

Hello, again not sure if this is the correct thread? I was doing some work at a commercial building and noticed at the overhead service drop (200 amp) connection of the neutral where it is crimped from the utility company that a big chunk of aluminum is missing. Looks like a giant squirell or something took a bite out of. About 50% of the connector and conductor is missing. Anybody see anything like that before? No trees around this.

 

[al hildenbrand]

I'd suspect that one of the hot service drop to service entrance conductor utility installed splices lost its protective cover at some point and later wind swinging of the drop got that splice in contact with the neutral splice.

I actually saw this on a corner of a residence, once. A true McGiver-esc display of spraying molten metal. The utility transformer overcurrent protection just didn't care, and the sparks kept happening.

 

[anderson100]

the wires are very clean and shiny? and the hots are taped pretty good?

 

[LEO2854]

Hello, again not sure if this is the correct thread? I was doing some work at a commercial building and noticed at the overhead service drop (200 amp) connection of the neutral where it is crimped from the utility company that a big chunk of aluminum is missing. Looks like a giant squirell or something took a bite out of. About 50% of the connector and conductor is missing. Anybody see anything like that before? No trees around this.

Somtimes water runs along the wire and there could have been a high wind storm that caused a short that cleared after the fact.:roll:

 

[mxslick]

I'd suspect that one of the hot service drop to service entrance conductor utility installed splices lost its protective cover at some point and later wind swinging of the drop got that splice in contact with the neutral splice.

I actually saw this on a corner of a residence, once. A true McGiver-esc display of spraying molten metal. The utility transformer overcurrent protection just didn't care, and the sparks kept happening.

As I have posted before in many other threads, Utility transformer fuses are NOT sized to protect against overloads, but are intended to only remove a shorted transformer from the system, hopefully before it explodes. Remember that utilities do NOT follow NEC rules for overcurrent device selection, and oil-filled transformers are routinely overloaded well in excess of what the NEC would allow "us" to do with a dry-type transformer like a 480 to 208/120.

With that said, I agree with your opinion on the cause of what the OP describes.

the wires are very clean and shiny? and the hots are taped pretty good?

Arced aluminum wire, especially after some exposure time, could appear clean.

In any event did you notify the POCO to come fix it before it lets go completely?

 

[nakulak]

are you absolutely sure that there were no giant squirrels around ?

 

[hurk27]

I have seen lightning strikes do this.

Ask home owners if there was anytime in the past they had equipment failed or knew of a lightning strike.

 

[mcclary's electrical]

I've seen it on three different residences in Richmond. The squirrels climb from trees onto power lines, walk over to the house, and chew on the bare grounded conductor to sharpen their teeth. Two of the three occasions, the wire eventually was cut clean in two damaging electronics, tv's, and microwaves in the houses. The third house, I simply saw it as I was working in the neighborhood, and I told the HO to call the power company. I don't know if anything was damaged in that house


One of the homes it happened to twice in two years. His solution was to lay big blocks of soft lead(not my recomendation) under the meter base and the squirrels would sharpen their teeth on that instead of the wire

 

[ptonsparky]

... His solution was to lay big blocks of soft lead(not my recomendation) under the meter base and the squirrels would sharpen their teeth on that instead of the wire

Hi speed Lead poisoning takes less time... . Usually has to be reaplied.

 

[Open Neutral]

Pole Pig overloads & fusing

Pole Pig overloads & fusing

As I have posted before in many other threads, Utility transformer fuses are NOT sized to protect against overloads, but are intended to only remove a shorted transformer from the system, hopefully before it explodes. Remember that utilities do NOT follow NEC rules for overcurrent device selection, and oil-filled transformers are routinely overloaded well in excess of what the NEC would allow "us" to do with a dry-type transformer like a 480 to 208/120.

So just curious; what kind of overload factors apply? I've seen three tiny pigs, that provide 3-ph to a dentist office, charred black after a storm. I assume something shorted and they cooked until flames came out.

I asked the line crew why there were 2 fuses in series on the primary of the one on my block. He said the 15A fastblow was for line hits in our frequent t-storms; the cheaper 10A was for normal overload clearing. Is that normal?

 

[brian john]

.

In any event did you notify the POCO to come fix it before it lets go completely?

In the past the utility had better response to issues like these, I have called the utility on several issues and they ignored to the point of failure. I am sure it it due to the tightening of their budgets, BUT in all cases it was more costly in the long run.

CT's not securly mounted on the bus, 3 months later the CT bus burnt open.

Pole smoldering I called it in, two days later it was on fire.

Overloaded transformer, the lineman told me when it blows we'll most likely do something, and they did.

Lastly I quized a lineman what size fuses he was installing after a fault on a transformer, he told me WITTS, What's in the truck.

 

[mxslick]

So just curious; what kind of overload factors apply? I've seen three tiny pigs, that provide 3-ph to a dentist office, charred black after a storm. I assume something shorted and they cooked until flames came out.

I asked the line crew why there were 2 fuses in series on the primary of the one on my block. He said the 15A fastblow was for line hits in our frequent t-storms; the cheaper 10A was for normal overload clearing. Is that normal?

I have been told that on pole-mounted, 200% "long term" and up to 300% "short term" is not uncommon. For pad mounts it is usually limited to 100% and 150% respectively. They did not define what they consider "long" and "short" term.

Oil-filled transformers are usually pretty robust and can tolerate these kinds of overloads, but with a reduction in overall internal insulation life. The POCO's (if they are on the ball) weigh the reduction in life with the costs associated with upsizing to balance maximum life and minimum cost, with a slight nod towards safety and violent failure risks.

In the past the utility had better response to issues like these, I have called the utility on several issues and they ignored to the point of failure. I am sure it it due to the tightening of their budgets, BUT in all cases it was more costly in the long run.

CT's not securly mounted on the bus, 3 months later the CT bus burnt open.

Pole smoldering I called it in, two days later it was on fire.

Overloaded transformer, the lineman told me when it blows we'll most likely do something, and they did.

Lastly I quized a lineman what size fuses he was installing after a fault on a transformer, he told me WITTS, What's in the truck.

Our local POCO (So. Calif. Edison) has, for the most part, been pretty fast with responses.

See THIS THREAD and THIS ONE.

When you spot a problem with POCO gear, you can speed up the response time considerably by giving them the pole/equipment number (IF and only if you can safely read that information) or the circuit name, which will be on the pole on a stencil-styled plate attached just above eye level usually.

In the case of the open vault in the first thread, I gave them the vault number which was on the vent pipe.

 

[SteveSivell]

I would have p.o.c.o. come out and repair the crimp. and as to the fualt current comments on the transformer and why the primary did not blow, mxslick is correct. Transformer is always interposed between a primary source and a secondary load. Therefore, the transformer poses an opposition (impedance) to current flow from source to load. "Percentage Impedance" (Z%) isThe voltage drop of a Transformer at full load due to the winding resistance and leakage reactance; that depends upon the power factor in the secondary circuit.
In the event of downstream fault, the effects of the fault on the circuit(and circuit components, such as overcurrent devices and other electrical equipment) will be lessened to the extent that transformer impedance increases. Impedance is a complex variable made up of both resistance and reactance , voltages must be viewed vectorially

The impedance is then the ratio of that primary voltage to the rated voltage; multiplying that by 100 gives the impedance in percent. , this determines the maximum fault current the transformer is capable of delivering to a downstream short-circuit.
Eample
1,000 kVA transformer
with a 5% impedance
480 volt secondary.
Rated full-load secondary current would be 1,200 amperes
current=KVA/(1.732 x KV) = current=1000/(1.732 x .480)
The maximum short-circuit current would be 1,200 divided by per unit impedance of 0.05. or 24,000 amperes. current=1200/(.o5) =24,000

 

[mxslick]

Thanks Steve for explaining that in the great detail you did. :grin: And welcome to the Forums.

.....I've seen three tiny pigs, that provide 3-ph to a dentist office, charred black after a storm. I assume something shorted and they cooked until flames came out.

OpenNeutral, kinda overlooked that in my last response, but two possibilities:

1: You saw the aftereffects of a lightning hit (or severe sustained overload);
2: There is a brand of transformer that is well known for very bad exterior paint and when it all weathers off you end up with a dull black can. (there is yet another brand, RTE, that the POCO guys call "Rust 'Till Eternity" because they get rusty fast. )

It is very rare, but I have been told of pots that have had virtually all of the oil boiled out of them and they kept working, but ran super hot and smelly.

Oh, and one of the worst smells is a burned-out POCO transformer, especially the older ones. Think moldy tuna, rank sneakers and smelly pits all together and you're about 1/10th of how bad it smells.:grin:

 

[LarryFine]

Oh, and one of the worst smells is a burned-out POCO transformer, especially the older ones. Think moldy tuna, rank sneakers and smelly pits all together and you're about 1/10th of how bad it smells.:grin:

Throw in a burned-out fluorescent ballast for good measure.

 

[Open Neutral]

1: You saw the aftereffects of a lightning hit (or severe sustained overload);

Oh, this was a T-storm. I doubt they were hit, as they are well shadowed by far taller church steeple w/Nextel site. Plus, my neighborhood is fed by one of those, and we'd know it.

My question was how would anything less than a major hit burn them like that? I can see a sustained overload setting the oil afire, but a hit would have left shrapnel around, not slow cooked 'em.

 

[mxslick]

Throw in a burned-out fluorescent ballast for good measure.

Yeah, that would bring it to about 2/10ths. :grin:

Oh, this was a T-storm. I doubt they were hit, as they are well shadowed by far taller church steeple w/Nextel site. Plus, my neighborhood is fed by one of those, and we'd know it.

My question was how would anything less than a major hit burn them like that? I can see a sustained overload setting the oil afire, but a hit would have left shrapnel around, not slow cooked 'em.

There have been cases where lightning hits have fried but not exploded the pots (can't say the same for the fuses).

If they are still working and you aren't having voltage issues, then they probably aren't fried, just badly painted or discolored from a previous overload.

If you get a chance, get some pics and post them here so we can see exactly how bad it is. :grin: