This suit by Aetna Insurance Company, the subrogated fire insurer of a building owned by Rose Brener, seeks recovery against H. J. Hintz of the amount of damage sustained in a fire which Aetna alleged was caused by Hintz’s negligence. Aetna has now appealed from the dismissal of its suit after a trial on the merits.

Brener had employed Hintz to install the electrical wiring for two central air conditioning units in September, 1968, when the building was entirely renovated. Brener’s tenants thereafter complained of a clattering in the condensing unit, which was replaced twice. In October, 1971 a fire oc*63curred, causing the damage upon which this litigation is based.

The principal fire damage was at the rear wall, just above the air conditioning condensing unit located on the outside of that wall. The cause of the fire was undoubtedly of electrical origin.

Two electrical defects or faults were found in the electrical wiring, and the ground wire had actually burned through and separated at the location of each fault. The upper fault was located in the electrical wire which lay on top of the wall plate (the horizontal timber at the top of the stud partition wall), at the point where Hintz had attached the wire by using a crimped nail, and the lower fault was located in the same electrical wire where it was dropped down between the vertical studs of the partition wall, at the level just above the disconnect switch which served the condensing unit. Either fault, by itself, could have caused the fire.

On appeal Aetna contends that the evidence preponderates in its favor, since it proved the upper fault was caused by Hintz’s improper use of a crimped nail, while the cause of the lower fault was not provable because of the effects of the fire.

At trial each side presented an expert electrical engineer experienced in investigating the origins of fires. George Hero had examined the premises after the fire. He found an area of copper beading about eight inches on either side of the break at the lower fault and concluded that arcing had occurred and generated heat for several minutes. At the upper fault only one bead had formed, but since the wire had burned through and since there was no other copper melted in the area except under the nail, he opined that arcing had also occurred there.

Hero attributed the upper fault to Hintz’s use of the crimped nail instead of an approved staple, allegedly in violation of the electrical code, explaining that use of a nail can cause concentration of pressure at one point and ultimate damage to the insulation.1 He concluded that an intermittent short had occurred in thisi area (explaining the intermittent clattering in the condensing unit), and that when the ground conductor burned loose at the nail, the short circuit was reestablished, and arcing occurred when the ground current found its way to ground through the metal pipes of the air conditioning system. His “simple answer” for the cause of the lower fault was that the wire in the stud' space was pierced by a nail of unknown origin or that some other damage of unknown origin had occurred in the insulation of the wiring.2 He concluded that arcing had occurred at both faults, but opined that the upper fault was the more probable cause of the fire, because intermittent shorting at that point was also the logical explanation for the clattering of which the tenants had complained.3

Joseph Leininger, on the other hand, had not inspected the premises, but did examine *64photographs (taken shortly after the fire) of the wiring in the area of both faults. He opined that if a short circuit had occurred in the upper area at the nail, no further energy would have been transmitted to the area of the disconnect switch, and the lower condition would not have occurred.4 He explained, however, that if the fire had originated in the area of the disconnect switch, the rising heat could have caused the nail (with a higher melting point than copper) to absorb and transmit heat, in turn causing the copper wire to burn through and separate near the nail. Furthermore, he found no evidence of arcing in the photographs of the wire break near the nail. He stated his opinion, based on the history, the photographs and the pattern of the burning, that the fire had originated in the rear wall near the disconnect switch, where the extensive beading was found, and that external heat had caused the relatively clean break in the wire at the location of the nail. In effect, he believed it was more probable that the fire caused the upper fault than that the upper fault caused the fire.

Aetna had the burden of proving that Hintz’s negligent act or omission caused the fire. The evidence in this case at best established that Hintz’s use of a crimped nail could cause a fire; the evidence taken as a whole, however, did not establish that Hintz’s conduct more probably than not caused this fire. It was at least equally probable (and in our view more probable) that the fire originated at the lower fault, for which Hintz was not shown to be responsible, and that the heat of that fire caused the break in the conductor at the nail.

The judgment is affirmed.

AFFIRMED.