What is the liability of a public utility when one of their transformer blows?

We just had the the second transformer blow in a week at the businees I own. I should specify that these are the transformers owned by our local electric utility company on the poles outside my shop. About a year ago we also had one blow on the same pole as these two.

Each time we informed the utility reponsible that we needed more power (bigger transformers) because we are drawing a lot of current. Everythng inside my shop is wired correctly and to code but the service provided by the utility is not robust enough to keep us running.

Each time a transformer blows up (and that’s what they do when they go, there is a loud explosion, accompanied by a flash of brilliant blue light of the type associated with thunderstorms often followed by smoke and transformer oil flying in the air) we lose several thousand dollars worth of equipment that we have to repair or replace and we lose the money we would have earned had we been running our machinery instead of waiting for them to fix the electricity.

Since the people at the utility seem to be adept at dodging any and all phone calls I was wondering if anyone had any experience in this area. I promise I won’t take your word as gospel but it would be nice to start forming an opinion as to how screwed we are. My partner is checking with our insurance company now to see if they will cover any of the damage but since this is not an act of God (unless He happens to be an incompetent electric utility employee) then I don’t see them being able to cover our losses.

So what is the straight dope? Will the utility reimburse me for my losses or do they have some form of sovereign immunity to claims such as these?

Not sure of your location, but this is for Utah:

Assuming your state is similar, you are probably out of luck in this regard. Normally, the utility is only responsible for providing safe, reliable power to the best of its ability. You might make a case that the power supply is unreliable, but I’m not familiar enough with the law to comment on that.

By the NEC, the utility company (a.k.a. the “service”) owns everything on your far side of the meter. I don’t know how long you’ve been in that location, but they ought (note “ought” instead of “should”) have done some load calculations when you originally moved into the place.

However, since you keep blowing tranformers, something tells me that either the power company didn’t:

[li]Check the phasing of the lines properly[/li][li]Your machinery is pulling a lot on one phase[/li][li]The power company didn’t provide you with a properly sized transformer for your loads.[/li][/list]

I just installed multiple transformers and switchgear down at Cannon AFB, and made sure that all the above were done. What kind of machinery are you using (something tells me they may not be using power capacitors to adjust for inducance due to your motors)?

I have half a clue. I need you to feed me more. . .

Oh, and what are you pulling? Like the primary to secondary (i.e. 4160/2400 to 120/208), and if you’re running three-phase or single.


Interesting. I just saw an article the other day about our power company (National Grid); they have a claims department and will make restitution for damage, etc. for any outages that are their fault. Lightning surges or falling tree limbs are not covered (Acts of God), but a blown transformer is their fault and they will make good.

Don’t know what your power company is, though, and their policy may be different (or they are not letting you know the facts).

Most of the time when a transformer blows, it’s not the physical transformer itself, but the transformer fuse (which can be replaced in just a few minutes). Are you saying the transformer itself is blowing up?

I’d say so, yes. Fusible links normal go without such drama.

You need to work your way up the food chain at the utility, until you get to the engineer level.
We played this game where I work for a month or so. Once I got the engineer on site, he had a truck there setting a new transformer the next morning.

I’ll second that puppy. If a fuse blows, your lights go out. When the transformer itself goes, it’s almost like a small bomb.

I saw a pole-mount can go once. It was cool. :cool:

However, since you keep blowing tranformers, something tells me that either the power company didn’t:

[li]Check the phasing of the lines properly[/li][li]Your machinery is pulling a lot on one phase[/li][li]The power company didn’t provide you with a properly sized transformer for your loads.[/li][/list]

There are only two machines on the transformer that has blown twice recently… A fairly large Air Conditioner (6-7.5 ton IIRC) which was just installed (and has now been properly fried at least once) and a machine that sorts letters (an MLOCR for those of you who may have experience with these machines) just like the ones the USPS has. It has several electrical motors but even at start-up pulls less than 70 amps. Similarly I am sure the AC does not pull more than 100 amps and each leg of the three phase is rated at 200 Amps min.

What is odd is that it is the other transformer of the pair on the pole that is pulling much closer to its rated current and it has only blown once. At any rate, the utility has had complaints/requests from us on each occassion that there is a failure but it is all to no avail. I also vaguely remember their coming out when we took occupancy of the building about 6-7 years ago and we indicated we would need more power at that point as well.

Just for information purposes, the first time this particular transformer went it looked like the fuse on the pole was the culprit. But when we disconnected power from the building and they replaced the fuse it immediately went again in a rather spectacular fashion… meaning that the transformer was toast in that instance as well.

Yeah, this is starting to sound to me like an unbalanced load. Are you sure you aren’t ground faulted on your machinery? If you’re using three-phase (which, if you’ve got “a pair”, I would suspect), and two of your coils are pulling 100A and your third is pulling 70A, something ain’t right, and after awhile, something’s going to go “boom”.

And in that case, it’s on your side of the meter, which unfortunately, is your problem. Do me a favor, and tomorrow, go look at the manufacturer’s plates on the machinery. That’ll help us all out quite a bit.
It’s just my educated guess, since I haven’t physically seen your equipment.

You haven’t had the local transformer blow during a really heavy thunderstorm before? Happens with some frequency in Houston- it’ll be raining like hell, then you’ll see a bright flash like lightning, except that it’s the wrong color, and hear a bomb-like thud (again, not lightning-like) and your power goes out instantly, and stays out for a while until the power guys can fix it.

The transformer itself has a fuse, in a residential line, about the width of a pencil, that is in a (basically) hollow tube. Normally, when a transformer “blows,” it is the fuse overheating and “exploding” the hollow tube. That occurs more commonly than transformer destruction.

Two years ago, I managed to witness both a tranformer fuse opening, and a transformer blowing up.

First was the fuse. A sharp crack (sounded like a golf ball being hit) and a bit of smoke drifting out of the transformer. The local utility comes out and replaces the fuse. The replacement fuse must have been made of pennies as the crew had no sooner gotten back into the truck when the whole thing went WHOMP with a bright flash and lots of smoke. Six hours later, they were back with a much larger transformer.

Actually, fusible links can go with a tremendous amount of drama…

You did mention that you have added a new air handler (6 - 7.5 tons) but didn’t mention whether it was larger than the previous unit you had. Also, have you always had the letter sorter? Are you the only load fed from the transformer bank.

You didn’t mention what your motor and lighting voltages were, but it sounds that you are fed with an open-delta bank supplying lights and power. 2 transformers can be hooked up such as to provide 3Ø power with the larger transformer sized to provide the additional 1Ø lighting load.

Do you happen to know whether the transformer ‘failure’ occured during the start-up of either your letter sorter or the air handler? Although full load current may indicate that you have sufficient supply, locked rotor current (the current required to turn the motor from a dead stop) is many times that of full load current and may be just enough when running at or above the transformer’s rating to cause the fuse to blow.

You should also check voltage. If the voltage is a bit low, it can indicate that the transformer may be a bit overloaded. If you find that your voltage is a bit low, request a recording voltmeter from your power company. This will help to verify your claim. Heck, request a recording voltmeter anyway, it will let the power company analyze your load and they may be able to either figure out that they need to upgrade their transformers or point to a possible problem on your side. Better yet, request a load audit and mention any additional load that has been installed since you first requested service.

As to your original question; Most power companies are not liable for 3Ø protection, loss of revenue, or equipment protection unless it can be shown that the damage was caused specifically by the power company (i.e. a crew hooks up 480 volts to a 240 volt service or they reverse rotation when reconnecting an established load). Most power companies have a claims department who deal with customer damage caused by power company equipment or personnel. Although the number is probably not listed, calling the main power company number and requesting to be transferred to Claims will usually get you through. If you can get no satisfaction that way, try contacting your Public Utilities Commission.

Fiat Lux,

OK, this is the information I have been able to glean thus far today. Our original configuration (up until the last boom-boom) was a two transformer Delta type with each transformer rated at 15kVA. The AC draws a maximum of 70 Amps if I am reading its faceplate correctly. The motors are half horsepower DC types that draw 3-5 Amps and there aren’t more than five of them. There is also a second AC on that line that draws 60 amps max and runs in the 45-60 amp range.

If someone knows how to do the math you can tell me if we are overloaded. Generally I remember that P=I*V but I also know there is a difference between peak, RMS, phase and line current etc… Without knowing how the utility rates their transformers I am at a bit of a loss (15kVA on each leg or all legs?). At any rate after the last boom-boom they brought us two spiffy new 25KVA transformers to replace the old ones. So far so good? BTW, we still haven’t had an engineer come out and actually look at anything even though they said they would send one out last year.

Now here is the interesting part. We measured the current and voltage at each leg where it comes into the building both loaded and unloaded. The results were;

Current Under Load - Where A, B and C are the three legs
A 150-180 Amps
B 156 Amps
C 30 Amps

This seemed odd given what we know about what is on each leg in our shop so we checked the Voltage to ground of each of the legs.
A 46V
B 231V
C 207V

And measured the voltage between legs
A-C 248V
A-B 239V
B-C 231V

This seemed odder still so we unhooked the building from the grid and measured the voltages coming into the building without our load attached. These measurements were made to ground.
A 290V
B 408V
C 200V
We ran a whole day’s production hooked up this way but after seeing these measurements we left the breakers to the building open and called the utility company.

The electrician who was making these measurements said that it looks like the power coming into the building is still not correct but he doesn’t know what would give us the results we saw. He said that our utility will probably pay for anything that is their fault and this looks like a mis-wiring? But that is just his opinion.

So what do you think guys? Will I get reimbursed or will I have to eat the damages and just what is going on with my building? I have 17 employees and don’t want to have to lay someone off to pay for the damages but there may not be much way around it.

I think others have already indicated that it depends. That is the best answer.

E.g., http://www.kscourts.org/kscases/supct/1999/19990709/82266.htm (In Kansas, utility could establish rules insulating it from liability for ordinary negligence, but not wilfull and wanton conduct).

Discussion of New York utility liability law

bibliography of legal resources on this issue (pdf)

Discussion of Indiana law on utility liability for power outages

Missouri case applying Kansas law

Cool, but only tangentially related article discussing telephone company’s liability for lightning strikes (pdf)

Article discussing insurance coverage for losses due to power outages

See pages 32-34 (pdf)

What?? Something is very, very wrong here. I can’t really speculate about what, without actually seeing the setup, but this needs looking into.

Oh, nevermind. You said it’s a delta-wired transformer, so it’s the line-to-line voltage that needs to balance, and it does, pretty much. Let me think this over a little more, and I’ll get back to you.


Are you running a straight 3Ø service? And what are the nameplate voltage and current (FLA) ratings of your motors? I originally assumed that you were drawing both lights and power off the transformer bank but it looks like this is a straight power bank and you are either getting your lights from another transformer or you are using ‘dry packs’ to get your 120/240 for lights and electronics. An easy way to tell would be to look at the transformer bank; if there are only 3 leads connected to it and the bare neutral wire of your service is not connected, it’s straight power.

On first blush, it looks like straight 240 3Ø power with either a grounded leg on the metering (some power companies ground one leg of the meter socket and only meter 2 legs figuring balanced load), or you have a leg laying against a ground on your side. What must be remembered on a straight 3Ø delta service as there is no ‘reference’ to ground; none of the transformer coils are grounded. As such, you can get all sorts of strange readings. What is telling to me is your first set of voltage readings (46, 271, 207). This indicates to me that you have a leg laying against a ground somewhere. If it truly is a delta system, this shouldn’t make a difference in the operation of your system; on a true delta service you can ground one leg and everything will work fine, it’s the second ground that will cause you problems. The second set of readings (248, 239, 231) is in line with a slightly unbalanced load (or if the taps on the transformers aren’t set correctly). The second warning flag is the readings after you disconnect your load from the power company (i am assuming that you opened your main breaker or switch). The only thing that throws me is the 408 volt reading after you isolated from the power company. Are you sure or was it actually 208?

I would recommend that you open all your breakers (or whatever disconnecting means you use) and close your main. Take voltage readings at the bottom of your main from each phase to ground. While i wouldn’t expect them to read the same (assuming again that this is delta), they should all be somewhere between say 200 & 280 volts. If they are, close breakers one at a time until you see readings similar to the 46, 271, 207. That branch of your circuit will be the one to troubleshoot; turn the power off and, starting at the load (motor or whatever) check all the connections back to the panel. Most often, the insulation on one of the motor connections wears through from the constant vibration.

Without a bit more info, this is the best i can offer.

Fiat Lux,