We have been regularly borrowing our neighbor’s sandwich maker for a while. Yesterday, our main power tripped while the sandwich maker was plugged in. My wife left it plugged in and forgot to unplug it when she flipped the main power switch back on. Later that day she noticed that it was still plugged but no longer hot. In general our power does not go out like that unless something shorted out and tripped it. We do not know if the sandwich maker broke because it itself shorted out the power and blew out (totally out of our control), or if it burned out because my wife left it in the plug after she turned on the power. The neighbors asked us to ask the shayla if we have any financial responsibility to pay them. (I assume not because we are shomer chinam, and there is no proof of negligence).
You should pay the value of the sandwich maker. This is less than a new one, and probably not much. It would be best to come to an agreeable compromise with the neighbor, for instance paying for half the
Your status as borrowers is not a shomer chinam, but rather a sho’el — a borrower.
Borrowers are liable for damages even for cases of ones — without any negligence.
However, they are not liable for cases in which the item breaks as part of its general use.
In this case, you cannot be sure: it is possible that the toaster broke as part of its use, and therefore caused the power to fall. In this case, you will be exempt from damages.
However, this does not seem likely. If the power fell on account of the toaster, it should have fallen again when you switched the power back on. If it didn’t, the indication is that the toaster broke later, on account of its being left on for too long.
In cases of safek — doubt as to whether damage was caused by use, or unrelated to use — there is a broad dispute among poskim as to whether the sho’el is liable or not. According to the Rosh (Bava Metzia 8:90), the borrower is liable, whereas according to the Nimmukei Yosef (citing from Ra’ah) the borrower is exempt.
Poskim are also undecided: The Shach (291:44) rules that the borrower is liable, and this is agreed upon by a number of poskim (see, for instance, Shut Toras Chaim 1:7), claiming that because there is a basic obligation to return the item, in cases of doubt the borrower is liable. The Ketzos Ha-Choshen (340:4), however, upholds the ruling of the Ra’ah, and exempts the borrower.
In our case, the safek as noted is weak, and becuase there is a clear peshi’a — leaving the toaster plugged in for a number of hours — the assumption is that it was broken by negligence, and the borrower is therefore liable to pay.