Gumz v. Northern States Power Co.

¶ 1. The petitioner, Northern States Power Company ("Northern States"), seeks review of a published court of appeals decision affirming a judgment of the circuit court for Marathon County entered in favor of James, Grace, Michael, and Susan Gumz.1 In this private nuisance action based on negligence, the Gumzs alleged that stray voltage from Northern States' distribution system caused damage to their dairy herd and also resulted in an invasion of and interference with the use and enjoyment of their property. After a jury trial, the circuit court entered judgment in favor of the Gumzs for damages in the amount awarded by the jury.

¶ 2. Northern States contends that the circuit court erred in the formulation of the special verdict. It asserts that the circuit court erroneously (1) failed to include a special verdict question asking whether the Gumzs commenced their lawsuit within the statute of limitations; (2) declined to give a special verdict question regarding whether the Gumzs were contributorily negligent in the management of their farm; and (3) refused to limit the damages only to those that occurred after Northern States had notice that stray voltage was harming the Gumzs' cows.

¶ 3. We conclude that the circuit court did not erroneously exercise its discretion in the formulation of the special verdict. Following precedent, we determine *269that the circuit court did not err in failing to include in the special verdict a question addressing the statute of limitations. Based on the facts of this case, the circuit court correctly concluded as a matter of law that the Gumzs' action was not time barred because they had exercised reasonable diligence in discovering that stray voltage from Northern States' distribution system was a cause of damages to their herd.

¶ 4. We also determine that the circuit court did not err in declining to give Northern States' proposed special verdict question regarding whether the Gumzs were contributorily negligent in the management of their farm. Finally, we determine that the circuit court appropriately allowed damages to be awarded for the period before Northern States had notice that stray voltage from its distribution system was harming the Gumzs' cows. Accordingly we affirm the court of appeals.

I — H

¶ 5. In 1981 James and Michael Gumz purchased a dairy farm from their parents, who had farmed at the location for many years. Northern States owns the electrical distribution system that serves the Gumzs' farm. Approximately the last mile of Northern States' distribution line to the farm consists of the original Copperweld conductor wire installed in 1937.

¶ 6. Around 1991, the Gumzs began to notice behavioral and physical problems with their herd. The cows showed signs of increased aggravation, "jumping" and "stepping around" during milking. The problem got worse over the next three years. The cows stopped drinking normally and appeared hesitant to drink out of their drinking cups. They exhibited nervous tail twitching and "dancing" (lifting their feet off the *270ground) during milking. The herd did not breed successfully enough to maintain its size, and milk production suffered.

¶ 7. In 1992 the Gumzs consulted their herd nutritionist, Dwight Tolk, regarding the health of their cows. Tolk observed that the cows did not come to the barn easily, walked stiff-legged, were thin, seemed sluggish, and did not lay down much. He monitored their behavior and worked with their nutrition. By approximately the summer of 1993 Tolk had ruled out the possibility that the problems were due to nutrition. Instead he believed that some "outside phenomenon . . . was causing the cows to be stressed and uncomfortable." He suggested to the Gumzs that the problem was due to stray voltage.

¶ 8. From 1994 through 1996 the Gumzs continued to work to improve the health of their herd. In the fall of 1994, the Gumzs began using Dr. Theresa Peterson as their primary herd veterinarian. Dr. Peterson testified that she was aware of some of the behavioral and health problems in cows that can result from exposure to stray voltage. However, she recommended that the Gumzs engage in a process of elimination of other causes before initiating testing for stray voltage. She testified that "I try to rule other things out before I get to the point of thinking about requesting electrical testing."

¶ 9. Around the same time they hired Dr. Peterson, the Gumzs also sought help for the herd's problems by hiring Rick Guralski to be the nutritionist for their milk cows. Tolk continued to work with the Gumzs' heifers.

¶ 10. Consistent with suggestions, the Gumzs tried to address the problems by changing their farming practices. They changed milking equipment, installing *271automatic take-off devices for their milking machines. The Gumzs also tried using different feeds and feed mills. In 1994, they switched to a new total mixed ration system designed to improve their feeding methods. An electrician who wired the barn addition for the ration system also checked the farm's wiring at that time. He determined that it was in good condition.

¶ 11. Despite these efforts the herd continued to deteriorate. At trial, Dr. Peterson testified that in late 1995 and 1996 she observed numerous health problems, including poor body condition, feet and leg problems, infections and mastitis, pneumonia, and weakened immune systems.

The cows had poor body condition, a lot of feet and leg problems. They started to look crippled. They had problems getting up, walked very slow, were lame, limping around. A lot of infections started, like mastitis outbreaks,... where the cow would become physically sick, and, without treatment, would go down and die. There was quite a bit of pneumonias at that time. A few uterine infections or nutritis cases. So their immune systems were becoming weakened.

In addition, she observed that there were numerous abortions and the herd had a poor fertility rate.

¶ 12. Dr. Peterson further testified that the problems with the Gumzs' herd were more difficult to alleviate than in other herds, and recently purchased animals that were healthy and vaccinated would get sick when they came to the Gumzs' farm. She ordered testing on blood and tissue but was still unable to isolate a particular disease causing the herd's problems.

¶ 13. In early 1996, after eliminating other potential causes, Dr. Peterson suggested to James Gumz that the farm be tested for stray voltage. On May 6,1996, Dr. Peterson wrote a letter to Northern States listing the *272herd's health problems and stating her opinion that the problems were due to stray voltage.

¶ 14. Later in May 1996, she prepared a report detailing the herd's health problems and her efforts to determine the cause of those problems. She described the management practices at the Gumzs' dairy farm as "above average," and stated that those practices "should allow a herd to remain healthy, produce quality milk, and have good production records." Ultimately Dr. Peterson concluded that the problems were not due to poor management, nutrition, or a specific disease. Rather, she stated that the poor health and performance of the herd were due to stray voltage and recommended that the farm be tested.

¶ 15. Consistent with Dr. Peterson's suggestion, the Gumzs had their farm checked for stray voltage by Northern States on May 7,1996, and by an independent electrician, John Ritchie, on May 14, 1996. Northern States' tests showed that the "cow contact voltage" was below the "level of concern." Using different testing equipment, Ritchie found much higher levels of voltage flowing onto the farm and determined that it was coming from off-farm.

¶ 16. Upon Ritchie's recommendation, the Gumzs installed an isolation transformer. After installing the device, the herd improved. Fewer animals died, the herd's food consumption improved, and the overall herd health increased.

¶ 17. In 1998 and 1999, the herd's health began to decline again. The Gumzs again asked Northern States to test for stray voltage, and again Northern States did not find voltage over the level of concern. They then hired another independent electrician, David Stetzer. Stetzer provided the Gumzs with equipment that monitored voltage on the barn floor. Measurements taken *273with that equipment indicated that as voltage decreased, milk production increased, and as voltage increased, milk production decreased.

¶ 18. On December 21, 2001, the Gumzs filed suit against Northern States for damages resulting from stray voltage from Northern States' system. Northern States moved for summary judgment on the ground that the Gumzs had not filed suit within the six-year period of limitations imposed by Wis. Stat. § 893.52.2 The circuit court denied the motion.

¶ 19. The case was tried to a jury. The Gumzs' causation expert testified that exposure to stray voltage had a substantial adverse effect on the herd's production. An agricultural economist testified that the total economic damages due to lost productivity were $901,183.

¶ 20. An expert for Northern States testified that the estimates of productivity adduced by the Gumzs were unrealistic, and maintained that the Gumzs' productivity levels were likely due to a variety of factors, not just stray voltage. He testified that there were a number of ways in which the herd was managed that likely harmed productivity. These included problems with herd nutrition, inconsistent feeding, inadequate biosecurity and disease prevention, and animal discomfort.

¶ 21. The jury found that Northern States was negligent with respect to the electrical service or facilities it provided to the Gumzs, and that Northern States' negligence caused damages attributable to harmful levels of electricity. It also found that Northern States' negligence caused damages to the Gumzs due to inva*274sion of or interference with the use and enjoyment of their land. It awarded the Gumzs total damages of $532,336.

¶ 22. The circuit court entered judgment in favor of the Gumzs, and Northern States appealed. The court of appeals affirmed, and Northern States petitioned for review.

HH hH

¶ 23. This case requires that we address whether the circuit court erroneously exercised its discretion in the formulation of a special verdict. A circuit court has wide discretion in determining the words and form of a special verdict. Hannemann v. Boyson, 2005 WI 95, ¶ 30, 282 Wis. 2d 664, 698 N.W.2d 714. We will not disturb a circuit court's determination unless the court has erroneously exercised its discretion.

¶ 24. A court erroneously exercises its discretion if the special verdict questions fail to cover all issues of fact or are inconsistent with the law. Estate of Hegarty v. Beauchaine, 2006 WI App 248, ¶ 46, 297 Wis. 2d 70, 727 N.W.2d 857. Whether a special verdict reflects an accurate statement of the law applicable to the issues of fact in a given case presents a question of law that we review independently of the determinations rendered by the circuit court and the court of appeals. Id.

H — l H-H

¶ 25. We turn first to Northern States' statute of limitations argument. The period of limitations for the Gumzs' lawsuit is governed by Wis. Stat. § 893.52. It *275provides that an action to recover for injury to property "shall be commenced within 6 years after the cause of action accrues or he barred... ."3 This court adopted the discovery rule in Hansen v. A.H. Robins, Inc., 113 Wis. 2d 550, 335 N.W.2d 578 (1983). Under the discovery rule, tort claims "accrue on the date the injury is discovered or with reasonable diligence should be discovered, whichever occurs first." Id. at 560. Actions for negligence in stray voltage cases are subject to the discovery rule. Kolpin v. Pioneer Power & Light Co., 162 Wis. 2d 1, 27, 469 N.W.2d 595 (1991).

¶ 26. Accrual requires that plaintiffs discover, or with reasonable diligence should have discovered, "not only the fact of injury but also that the injury was probably caused by the defendant's conduct...." Borello v. U.S. Oil Co., 130 Wis. 2d 397, 411, 388 N.W.2d 140 (1986). Plaintiffs can rely on the discovery rule only if they have exercised reasonable diligence in the discovery. Spitler v. Dean, 148 Wis. 2d 630, 638, 436 N.W.2d 308 (1989).

¶ 27. Northern States maintains that there is a question of fact as to whether the Gumzs exercised reasonable diligence in discovering that stray voltage from Northern States' distribution system was the cause of damage to their herd. It argues that under the discovery rule, there is a question of fact as to whether the Gumzs' action is barred by the statute of limita*276tions. Northern States therefore claims that the circuit court erred in not providing a separate special verdict question regarding whether the Gumzs knew, or with reasonable diligence should have known or discovered, that electricity from Northern States caused damage to the dairy herd by December 21, 1995, six years before the Gumzs commenced this action.

¶ 28. We disagree. The statute of limitations question falls squarely within the scope of Kolpin and Allen v. Wisconsin Public Serv. Corp., 2005 WI App 40, 279 Wis. 2d 488, 694 N.W.2d 420.

¶ 29. Like the present case, Kolpin involved the application of the discovery rule in a lawsuit for damages to a dairy herd caused by stray voltage. 162 Wis. 2d at 7-8. In March 1977 the Kolpins first noticed behavioral problems in their herd, including refusing to enter the milking parlor, poor eating and drinking, increased milking time, and a dramatic increase in mastitis. Id. at 11.

¶ 30. The Kolpins consulted their veterinarian and had experts check their equipment, but they did not find any problems. In 1980, after reading about stray voltage in a magazine, Mr. Kolpin and an electrician checked for voltage in the milking parlor. Although they found voltage, they did not know what the readings meant. Id. at 12. Mr. Kolpin then contacted the utility company, Pioneer, which sent a representative who did not know how to measure for stray voltage. Shortly after, a representative of the Public Service Commission took voltage readings on the farm, but did not communicate the results to the Kolpins. Id. at 12-13.

¶ 31. The Kolpins made some changes to electric motors and circuitry suggested by the Public Service Commission representative, and Pioneer made changes in its system that led to a drop in voltage in the Kolpins' *277barn. However, the herd's problems did not abate. Id. at 13. In 1983, the Kolpins hired an electrical contractor to install a grounding device, after which the herd's behavior and milk production returned to normal. The Kolpins filed suit against Pioneer in 1987. Id. at 14.

¶ 32. The case was tried to a jury, which found Pioneer liable for damages. Id. at 15. The jury also answered "yes" to a special verdict question asking whether the Kolpins knew, "or should they with the exercise of reasonable care have known, prior to February 17,1981, that Pioneer's electrical distribution system was a cause of damage to their dairy operation?" Id.

¶ 33. On review, this court concluded that the jury's answer to the question of discovery should be changed as a matter of law. Relying on Borello, 130 Wis. 2d 397, the court determined that for the Kolpins' action to accrue, "they must have objectively known, at that time, the cause of their injuries and Pioneer's part in that cause." Kolpin, 162 Wis. 2d at 25-26.

¶ 34. The court recognized that by 1980 Mr. Kolpin knew of the possibility of stray voltage, had discovered voltage readings on his farm, and had a hunch that stray voltage was his problem. However, it was not until the Kolpins installed the grounding device and the herd improved that the Kolpin's "objectively knew that Pioneer's distribution system, and not their own farm operation, was the cause of their problem." Id. at 26. Because of the difficulty of identifying the cause of stray voltage, "[t]he 'discovery' was more of a process of elimination of possible causes rather than a process of determination of the cause." Id. at 27. The court therefore concluded that as a matter of law, the Kolpins neither discovered nor with the exercise of reasonable care should have discovered, prior to February 17, 1981, that stray voltage from Pioneer's distri*278bution system was the cause of the damage to their herd. Id.

¶ 35. The court of appeals recently applied Kolpin to another stray voltage action in Allen, 279 Wis. 2d 488. The plaintiff in Allen first experienced problems with his dairy herd in 1976. He suspected stray voltage by 1988 and asked Wisconsin Public Service Corporation (WPS) to check his farm. WPS did not discover any stray voltage. Id., ¶ 3. Between 1984 and 1997, Allen worked with nutritionists, purchased a new mixer feed wagon, and installed a new milking parlor. However, the problems persisted. Id., ¶ 13.

¶ 36. In 1997 Allen hired an electrician who concluded that stray voltage from WPS was present on the farm. Id., ¶ 5. WPS again checked the farm, but it could not find the stray voltage. Id. Also in 1997, Allen installed an isolation unit, which improved production for just a few days. Id. The following year, he installed a different isolation unit, and herd behavior and production finally improved. Id., ¶ 14. Allen filed suit in November 2000. Id., ¶ 7.

¶ 37. WPS argued that Allen's claims were barred by the statute of limitations. It maintained that had Allen acted with reasonable diligence, he would have discovered that stray voltage from WPS was the cause of his problems more than six years prior to the date he filed the lawsuit. Id., ¶ 9. Relying on Kolpin, the court of appeals determined that Allen exercised reasonable diligence because he went through a reasonable process of elimination to find the source of the problem. Id., ¶ 16. Thus, it concluded that Allen "did not know nor could he have known through reasonable diligence that WPS was the cause of the herd's problems" until the isolation unit was installed and herd health improved in 1998. Id., ¶ 12.

*279¶ 38. In the present case, the circuit court followed the reasoning in Kolpin and Allen4 In its decision on Northern States' motion for summary judgment, the court described the Gumzs' efforts to "root out the cause of the problems" prior to 1996 as a "process of elimination" similar to that of the plaintiffs in Kolpin. Accordingly, it determined that the Gumzs "exercised reasonable diligence in determining the cause of their injuries and the defendant's role in that cause." Further, it concluded that the cause of action did not accrue until 1996, when the farm was tested for stray voltage and the Gumzs installed the isolation transformer.

*280¶ 39. At the jury instruction conference the circuit court reiterated its view regarding the plaintiffs' reasonable diligence. Northern States requested a special verdict question asking "Did the Gumzs know or with reasonable diligence should they have known or discovered that electricity from [Northern States] was a cause of damage to their dairy herd by December 21st, 1995?" The court recounted the Gumzs' efforts to pinpoint the cause of the problems and determined as a matter of law that they had exercised reasonable diligence. It also noted that, similar to Allen, Northern States had conducted tests but was unable to find the stray voltage. The court therefore concluded that under Kolpin and Allen the special verdict question addressing the statute of limitations should not be given.

¶ 40. Northern States contends that the Gumzs failed to exercise reasonable diligence because they were alerted to the possibility that stray voltage was a cause of damage in 1993, but failed to test for stray voltage until 1996. This argument misses the mark.

¶ 41. The Gumzs were advised about the possibility of stray voltage by their nutritionist, Dwight Tolk. At the time Tolk suggested stray voltage, there were still many possibilities to be eliminated before they would know that stray voltage from Northern States was causing the problems. The Gumzs exercised reasonable diligence in ruling out the other possibilities. Declining to follow the advice of a single non-expert in such circumstances does not demonstrate a failure to exercise reasonable diligence.5

*281¶ 42. Northern States also urges this court to examine the court of appeals decision insofar as it based its statute of limitations determination on the answer to a special verdict question pertaining to negligence. In Allen, the court of appeals offered two rationales for its conclusion that the plaintiff exercised reasonable diligence in investigating his herd's problems. First, as discussed above, the court determined that under Kolpin, Allen exercised reasonable diligence as a matter of law. 279 Wis. 2d 488, ¶ 16.

¶ 43. In addition, the court determined that the jury instruction and special verdict had adequately addressed the issue. The jury instruction stated:

The failure to exercise ordinary care to discover an unsafe electrical condition on the farm, even if it does not involve his own equipment, can also be negligence. However, if the defective electrical condition on the farmer's equipment or facilities is such that it was not known or would not have been discovered by the exercise of ordinary care, the farmer is not negligent in permitting it to exist in such condition.

Id., ¶ 17. The special verdict asked whether Allen was "negligent in the use of electricity on his farm," to which the jury answered "no." Id.

¶ 44. The court of appeals reasoned that for the jury to reach its conclusion, it would have to have determined that Allen exercised ordinary care to discover an unsafe electrical condition on his farm, as per the jury instruction. Id. Thus, the court concluded, the jury had in effect answered the question of whether Allen had exercised reasonable diligence with respect to the discovery rule and the statute of limitations. Id.

*282¶ 45. In the present case, the jury was given a similar instruction, followed by special verdict question 3, which asked whether the Gumzs were "negligent in the use and/or discovery of electricity on the farm." As in Allen, the jury answered the question "no." Following Allen, the court of appeals concluded that the instruction and special verdict question "effectively asked whether the Gumz[s] acted with reasonable diligence." 295 Wis. 2d 600, ¶ 13.

¶ 46. The court of appeals' approach in Allen and in this case is problematic. It infers that an answer to a negligence special verdict question provides an answer to a statute of limitations special verdict question. In Allen, the answer to whether the plaintiff was negligent in the "use" of electricity does not provide an answer to whether the plaintiff was negligent in the discovery of electricity.

¶ 47. With respect to the present case, the special verdict question asking whether a plaintiff was "negligent in the use and/or discovery of electricity" asks three questions: (1) is the plaintiff negligent in the use of electricity, (2) is the plaintiff negligent in the discovery of electricity, and (3) is the plaintiff negligent in both the use and discovery of electricity?

¶ 48. Here, the jury answered the special verdict question "no," which implies a negative answer to each of the three sub-questions. However, if the jury had answered the special verdict question "yes," it would have been unclear which of the three sub-questions the jury was addressing. That is, the jury could have answered "yes" to the special verdict question because the plaintiff was negligent in the use of electricity, in the discovery of electricity, or in both the use and discovery of electricity. Thus, an affirmative answer to the special verdict question here does not necessarily *283provide an answer to the question of whether the plaintiff was negligent in the discovery of electricity.6

¶ 49. Statute of limitations defenses based on failure to exercise reasonable diligence will often present questions of fact appropriate for a jury. When they do, courts should provide separate questions for negligence and reasonable diligence in discovery. To the extent that Allen and the court of appeals decision in this case imply otherwise, they are incorrect.

¶ 50. In the present case, however, the circuit court did not include special verdict question three to determine whether the Gumzs exercised reasonable diligence in discovering electricity. Rather, it determined as a matter of law that they exercised reasonable diligence and that the action was not time barred. Having determined the statute of limitations question as a matter of law, there was no need to include such a question in the special verdict.

¶ 51. The circuit court's analysis is correct. The Gumzs were as diligent in their efforts to learn the cause of their herd's problems as the plaintiffs in Kolpin and Allen. They worked with different nutritionists, tried different feeds, and changed feeding systems. They changed milking equipment. They had an electrician check the barn's electrical system to see if it was the cause of problems. They sought the help of Dr. Peterson, who looked for underlying diseases.

¶ 52. After ruling out these possibilities, the Gumzs had Northern States and another specialist *284check for stray voltage. They installed an isolation transformer when a single test indicated that stray voltage from Northern States was present. Because the herd's health improved after the installation of the isolation transformer, the Gumzs were finally able to pinpoint the cause of the problems.7

¶ 53. As in Kolpin, the Gumzs' discovery "was more of a process of elimination of possible causes rather than a process of determination of the cause." 162 Wis. 2d at 27. Further, the Gumzs' efforts constitute "a reasonable process of investigating the cause of [their] problems by eliminating other possible causes." Allen, 279 Wis. 2d 488, ¶ 16.

¶ 54. Also like Kolpin, the Gumzs did not have objective knowledge that stray voltage from Northern States was a cause of damages to their herd until the herd improved upon the installation of the isolation transformer in 1996. See Kolpin, 162 Wis. 2d at 27. Further, similar to Allen, the defendants had the opportunity to discover the stray voltage on the Gumzs' farm. Their inability to do so is at odds with the claim that with reasonable diligence the Gumzs should have known that stray voltage was a cause of damages.

¶ 55. In sum, we determine as a matter of law that the Gumzs exercised reasonable diligence. Prior to *285May 1996 the Gumzs did not know, nor with reasonable diligence should they have known, that stray voltage from Northern States was a cause of damages to their herd. Accordingly, we determine that the circuit court did not erroneously exercise its discretion in declining to include a special verdict question concerning the statute of limitations.8

*286IV

¶ 56. We consider next Northern States' contributory negligence argument. Northern States contends that the circuit court erred by framing a special verdict question that was limited to the Gumzs' negligence "in the use and/or discovery of electricity on the farm." It argues that it was entitled to a broader question of whether the Gumzs were "negligent in the operation, maintenance or management of their dairy enterprise."

¶ 57. At the jury instruction conference Northern States asserted that a negligence question limited to electricity was too narrow. It maintained that the case is primarily about all of the Gumzs' lost productivity, that the Gumzs' management of the farm was negligent, and that their negligence contributed to their overall lost productivity. In contrast, the circuit court determined that the case is about damage caused by stray voltage. The court explained its position as to the form of the question as follows:

*287It seems to me that where this case is at is there is the argument that the electrical services and facilities have caused damage, and in large part the defense is that it was not the electrical services or facilities that caused the damages, rather it was a litany of things .... The number of cows, lactation, history, the management of the herd, genetics, feed, water intake, herd health, mastitis, and perhaps other things. But that captures the essence of a significant part of the defense put forward. And it seems to me that the jury is going to be asked to answer what, if any, damage electricity caused, and certainly the defense is free to argue that there was none, or it was minimal. It was all of these factors.

¶ 58. The court emphasized that the defense could argue that any damages sustained were caused by the Gumzs' negligent operation of the farm and not by stray voltage:

[M]y ruling on that is that the issue in this case is damages that were caused, if any, by electricity — and the defense can argue from a cause standpoint that the electricity didn't cause any damage or was minimal and these other factors went into it, but in terms of contribution, I'm not instructing that those other factors that we've talked about earlier can enter into a determination as to contribution. It's just the Gumzs' responsibility concerning the electricity that figures into the contribution.

I think you can still explore your theory, argue your theory that electricity didn't cause these damages, that something else did, and you reinforce to the jury that the only thing that the plaintiffs can recover for ... are damages caused by the negligent service or facilities provided relative to electricity.

¶ 59. The circuit court's reasoning is reflected in the negligence questions in the special verdict, which *288concern negligence regarding electricity and electrical service. The special verdict provides in relevant part:

Question 1: Was Northern States Power Company negligent with respect to the electrical service or facilities which it provided to the Gumz farm?

[Jury answered ’Yes."]

Question 2: If you answered Question 1 "yes," then answer this question: Was this negligence a cause of damages, attributable to harmful levels of electricity, to the Gumzs?

[Jury answered 'Yes."]

Question 3: Were the Gumzs negligent in the use and/or discovery of electricity on their farm?

[Jury answered "No."]

Question 4: If you have answered Question 3 "yes," then answer this question: Was the Gumzs' negligence a cause of damages, attributable to harmful levels of electricity, to the plaintiffs?

[Jury did not answer.]

Question 7: If you have answered Questions 2 and 4 "yes," then answer this question: Assuming that the total cause of damages attributable to harmful levels of electricity is 100 percent, what percentage of the causal negligence which you have found do you attribute to:

A. Northern States Power Company_%

B. The Gumzs _%

*289[Jury did not answer.]

With respect to damages, the special verdict explicitly limited the potential damages to those resulting from electricity:

Question 8: What sum of money will fairly and reasonably compensate the Gumzs for damages attributable to harmful levels of electricity as to:

A: Lost milk production [Jury answered $249,086.]

B. Loss of fair market value to their dairy herd [Jury answered $33,250.]

C. Excess costs [Jury answered $50,000.]

D.For annoyance, inconvenience, and loss of use and enjoyment of their real property [Jury answered $200,000.]

(Emphasis added.)

¶ 60. The jury instruction also was explicit that damages could be awarded only for harms due to electricity. The instruction provides in relevant part:

As to [special verdict questions] 8A, 8B and 8C,

If you are satisfied that plaintiffs have in the past experienced damages because their dairy herd was exposed to harmful levels of electricity, you shall award such sum of money as will reasonably compensate plaintiffs for the loss attributable only to that electricity. You cannot award any damages for any condition of the Gumzs' herd except insofar as you are satisfied that the herd's condition has been aggravated by harmful levels of electricity. If you find that the plaintiffs had a condition which was aggravated because of harmful *290levels of electricity, then you should include an amount which will fairly and reasonably compensate the plaintiffs for such damages the plaintiffs suffered as a result of such aggravation.

Any damages that the plaintiffs may have suffered, or have, which is not the natural result of harmful levels of electricity, is not to be considered by you in assessing damages. You cannot award damages for any condition which has resulted from consequences which are attributable to causes other than harmful levels of electricity. ...

If livestock has been damaged, and the injury to the livestock has ceased, the compensation to be awarded to the owner is the difference between the fair market value of the cattle had the herd not been exposed to harmful levels of electricity, and the value of the dairy herd after the harmful levels of electricity ceased.... 9

(Emphasis added.)

¶ 61. The jury instruction was carefully tailored to match the special verdict questions. The instruction advised the jury eight times that damages due only to harmful electricity could be awarded.10

¶ 62. While the special verdict did not ask whether the Gumzs were negligent in managing their *291farm, neither did it allow that damages could be awarded for any injury due to their farm management. Similarly, the jury instruction explained repeatedly that damages were limited to damages from electricity. Thus, the special verdict was tailored to allow the Gumzs to recover for damages due to Northern States' negligence while preventing them from receiving any award for lost productivity due to their farm management.11

*292¶ 63. Nonetheless, Northern States contends that the circuit court's approach is erroneous. Relying on this court's decision in Morgan v. Pennsylvania Gen. Ins. Co., 87 Wis. 2d 723, 275 N.W.2d 660 (1979), Northern States maintains that there can be multiple "causes in fact" of an injury and that the Gumzs' poor management of the farm is a "cause in fact" of the damages. Northern States argues that it is therefore entitled to a special verdict question on negligent management.

¶ 64. Northern States' argument is unpersuasive. To begin, the primary case Northern States adduces for support is not on point. Morgan involved property damage caused by a motorist who ran into the plaintiffs trees. Following the advice of the motorist's insurance *293adjuster, the plaintiff drove stakes into the ground next to the damaged trees for support. Id. at 728-29. In doing so, the plaintiff suffered a hernia. Id. The circuit court dismissed the complaint, but this court reversed. It determined that if the adjuster's conduct was a substantial factor in producing the injury, it could constitute cause-in-fact for the purpose of negligence. Id. at 735.

¶ 65. The issue presented here, however, is not whether poor farm management could be a substantial factor in producing an injury or whether there can be multiple causes in fact for an injury. Rather, the issue is whether the relevant inquiry in this case can focus narrowly on management of the electricity or must look more broadly at the Gumzs' management of their farm. Morgan provides no guidance whatever on that question.

¶ 66. Next, Northern States argues that it is entitled to a special verdict question on negligent management because the damages cannot be separated. It asserts that there is a single injury caused "concurrently" by electricity and the Gumzs' farm management, and that the Gumzs' management is therefore contributory to the damages sought. This argument is also unpersuasive. It is common in Wisconsin law that juries must differentiate damages due to the defendant's negligence from the plaintiffs prior condition or from damages caused by other parties.

¶ 67. For example, medical malpractice cases often require that juries separate the damages caused by a physician's negligence from damages that are "the result of the natural progression" of the condition or injury.12 *294Where negligence aggravates a plaintiffs pre-existing injury, Wisconsin juries must separate out the prior injury and provide compensation only for the aggravation.13 In enhanced injury cases, juries must distinguish damages from a plaintiffs initial accident from the damages caused by a defendant's actions that "pro-duc[e] injuries over and above what probably would have been sustained in the [accident]."14

¶ 68. Similarly, the special verdict in the present case requires the separation of damages to the herd stemming from different conduct. The damages to the Gumzs' herd caused by Northern States' negligence may be "concurrent" with damages to the herd resulting from the Gumzs' management of their farm. Nonethe*295less, the jury was required to assess damages attributable only to harmful levels of electricity.

¶ 69. Generally we accord wide discretion to the circuit court in framing the special verdict as long as it covers all issues of fact in the case and is consistent with the applicable principles of law. Hegarty, 297 Wis. 2d 70, ¶ 46. While we acknowledge that the circuit court could have framed the question more broadly, it was not required by the facts or law to do so here. Instead, the court exercised its discretion by carefully tailoring the questions to have a consistent focus. Both the negligence and damage questions were focused on electricity. Accordingly, we determine that the circuit court did not erroneously exercise its discretion in declining to give Northern States' proposed question regarding the contributory negligence of the Gumzs' management of their farm.

V

¶ 70. Finally, we turn to Northern States' argument that the circuit court erred in refusing to limit damages only to those that occurred after Northern States had notice that stray voltage could be harming the Gumzs' cows. The Gumzs contend that Northern States has waived the issue under Wis. Stat. § 805.13(3) because it failed to raise it at the jury instruction conference.

¶ 71. Wisconsin Stat. § 805.13(3) provides in relevant part:

(3) Instruction and Verdict Conference

The court shall inform counsel on the record of its proposed action on the motions and of the instructions *296and verdict it proposes to submit. Counsel may object to the proposed instructions or verdict on the grounds of incompleteness or other error, stating the grounds for objection with particularity on the record. Failure to object at the conference constitutes a waiver of any error in the proposed instructions or verdict.

¶ 72. In our review of the transcript of the jury instruction conference we could not discern that Northern States sought a special verdict question limiting damages. Further, our review indicates that Northern States did not raise an objection based on failure to limit damages. We therefore conclude that Northern States' failure to preserve the issue at the jury instruction conference constitutes a waiver under § 805.13(3).

¶ 73. This court has the discretion to review an issue that has been waived when it involves a question of law, has been briefed by the opposing parties, and is of sufficient public interest to merit a decision. Apex Elecs. Corp. v. Gee, 217 Wis. 2d 378, 384, 577 N.W.2d 23 (1998); Wirth v. Ehly, 93 Wis. 2d 433, 444, 287 N.W.2d 140 (1980). The present issue is one of law, the parties have briefed it, and stray voltage cases are of substantial public interest. We therefore address the issue to provide guidance to litigants in future cases.

¶ 74. Northern States contends that under Snyder v. Oakdale Co-op Elec. Ass'n, 269 Wis. 531, 69 N.W.2d 563 (1955), a utility is not required to inspect customer premises unless the utility has notice of a problem, and that a utility may be liable for damages only when it supplies electricity knowing of a condition that causes injury. Snyder, however, is inapt.

¶ 75. The plaintiff in Snyder requested electrical service from the defendant utility. An inspection report *297filed with the defendant indicated that there were defects in the plaintiffs electrical system. However, the defendant provided service, causing a fire which damaged the plaintiffs property. Id. at 531-32. The court determined that a company providing electricity "for use in a private wiring system is not under obligation to inspect such system before supplying the current nor is it obligated to respond in damages for injuries sustained by reason of the defective condition of such system" unless the company knew of the defects. Id. at 533.

¶ 76. Thus, Snyder concerns obligations of utilities in supplying electricity to defective private wiring systems. The present case, however, does not involve a defective private wiring system. Rather, the stray voltage causing damage to the Gumzs' herd came from Northern States' system. The fact that a utility must have notice of defects in private electrical systems in order to be responsible for damages is irrelevant to the question of whether notice is required for a utility to be responsible for damages caused by the utility's system.

¶ 77. Moreover, Northern States'argument that it cannot be liable for negligence without notice of a problem understates the standard of care. As stated in the jury instruction, the electric company must exercise "ordinary care to discover any unsafe or defective condition of its distribution system ...." It is contradictory to predicate the requirement to exercise ordinary care in discovering unsafe or defective conditions in its distribution system on having notice of those unsafe or defective conditions.

¶ 78. Northern States' argument is also inconsistent with Kolpin, Allen, and Vogel v. Grant-Lafayette Elec. Coop., 201 Wis. 2d 416, 548 N.W.2d 829 (1996). In *298each of those cases, utilities were found liable for damages caused by stray voltage, even though the utilities did not know that stray voltage from their systems was causing damage to the plaintiffs. Kolpin, 162 Wis. 2d at 11-14; Allen, 279 Wis. 2d 488, ¶¶ 3-7; Vogel, 201 Wis. 2d at 419-21. Consistent with these cases, we determine that the circuit court appropriately allowed damages to be awarded for the period before Northern States had notice that stray voltage from its system was harming the Gumzs' cows.

VI

¶ 79. In sum, we conclude that the circuit court did not erroneously exercise its discretion in the formulation of the special verdict. Following precedent, we determine that the circuit court did not err in failing to include in the special verdict a question addressing the statute of limitations. Based on the facts of this case, the circuit court correctly concluded as a matter of law that the Gumzs' action was not time barred because they had exercised reasonable diligence in discovering that stray voltage from Northern States' distribution system was a cause of damages to their herd.

¶ 80. We also determine that the circuit court did not err in declining to give Northern States' proposed special verdict question regarding whether the Gumzs were contributorily negligent in the management of their farm. Finally, we determine that the circuit court appropriately allowed damages to be awarded for the period before Northern States had notice that stray voltage from its distribution system was harming the Gumzs' cows. Accordingly we affirm the court of appeals.

By the Court. — The decision of the court of appeals is affirmed.