Central to the mitzvah of Kashrut is ensuring that the dishes and other utensils used in a Jew’s kitchen are kosher – and rectifying the situation when things go wrong.
In this essay, we will explore the method of kashering through steam, looking specifically at countertops. In order to understand if and when this method of kashering is appropriate, we will take a whistle-stop tour through the basic laws of kashering utensils, including those which can’t be kashered in a normal manner, and whether one must be concerned for special cases. We will then briefly explore the problems which could arise in a normal kitchen with countertops, including the laws of solid foods which spill. Once we have sketched the basic laws and understand the potential problems, we will take a deeper look at what exactly steam is from a halachic perspective. From there we will explore a foundational principle of kashering utensils – k’bol’o kach polto (one purges a utensil of its non-kosher absorptions in the same manner as it acquired them), in depth. Once we understand how steam works in light of this principle, we will turn our attention to the making of steam today – is a heating element sufficient for the kashering process, or must one utilize actual fire? In the last section, we will note some of the opinions of Acharonim in our time.
Hagala – Kashering Through Boiling Water
When the Jews waged war on the Midyanites in the desert, they took spoils which included cooking utensils. Faced with the issue that these utensils were used to cook non-kosher food, the Torah provides us with a way to “kasher” the vessels: “Gold, silver, bronze, iron, tin, lead and anything else that which is used in fire must be put through the fire, and then it will be clean. But it must also be purified with the water of cleansing. And whatever is not used in fire you shall pass through water.” Based on these verses, the Gemara lays down the major principle of Kashrut – the way that a vessel was used is the way that it must be kashered. If it was used cold, then it simply requires washing; if it was used with hot liquids, it needs to be boiled in water; if it was used with dry heat, it must be heated until it is white-hot. This principle is codified by the Rishonim, and applies to all vessels which were used for non-kosher, or which contain absorptions of a forbidden food – meat and milk and chametz included. In addition to codifying this rule, the Rishonim also extended it – if something was used only in a kli sheini, it is sufficient to kasher that utensil in a kli sheini and not in a kli rishon. This is how the Shulchan Aruch rules, and the Mishna Berura there explains that this is an application of the principle that the Gemara established – k’bol’o kach polto. The Rema writes that the custom has become to kasher every utensil that requires immersion in a kli rishon, regardless of how it absorbed.
A Vessel which is Too Big or Otherwise Unsuitable for Traditional Hagala
The question arises, in light of the above, how one is able to kasher a utensil which is too big or otherwise unable to be immersed in boiling water.
In some cases, this is not a problem – for example where the relevant absorption happened in a kli sheini. In this case, the maximum level and quality of forbidden taste absorbed in the vessel is a klipa and it can therefore be kashered through a process called irui. Tosafot and the Rosh record a dispute between the Rashbam and the Ri with regards to the status of irui – the Rashbam thinks that it is comparable to a kli sheini, whereas the Ri thinks that it is comparable to a kli rishon. The Rema, in his commentary on the Beit Yosef, writes that we rule like the Ri and consider irui from a kli rishon to be like the kli rishon, and therefore effective in creating an absorption or expulsion of taste; however, the Rema writes there that this is only true to the extent of a klipa. Therefore, the first thing that one can do is pour boiling hot water from a kli rishon on to the utensil which is too big to be kashered. This method works, though, only for those things which have not been used on a fire, and therefore have themselves only ever absorbed, at a maximum, through irui.
There are times, however, where a particular vessel requires full immersion in a kli rishon – “hagala”, but is simply too big to fit into the requisite pot. In this case, the Beit Yosef quotes the Rabbeinu Yerucham who suggests that one may fill the vessel with boiling water (which at this point is not sufficient to kasher the utensil, since it has been removed from the fire and poured into another vessel) and then place a red hot stone inside the water. This process causes the water to re-boil and overflow the sides, thus kashering the pot. The Hagahot Maimoniot is quoted there as ruling that this process is equivalent to proper hagala. This ruling is later codified by the Shulchan Aruch, including the ruling of the Hagahot Maimoniot. However, the Mishna Berura writes that there are those authorities who don’t recognize the efficacy of this form of hagala, and equate it, at a maximum, with irui. In his longform Bi’ur Halacha, the Mishna Berura expands on this opinion, quoting the Pri Chadash and other authorities, and rules that one may not use this form of kashering unless the utensil absorbed through irui or at the very least is considered aino ben yomo. Elsewhere, the Mishna Berura rules formally that one must not use this form of kashering ab initio unless the vessel is aino ben yomo.
Rov Tashmisho – A Utensil’s Normative Use
A further question arises when considering how to kasher a particular utensil. There are many utensils which have a normative use – a tea spoon for instance, will normally be used for tea or coffee and therefore could be kashered in a kli sheini – but it could sometimes be used for other things, e.g. to stir a soup pot, and would therefore require a kli rishon. The Rishonim debate whether or not one must take these outlying cases into account when kashering a utensil. According to the Ra’avyah, one must always be careful to kasher a given utensil in the most stringent way that it might have been used. For example, if one normally uses a bowl for soup (kli sheini), but at times uses the bowl as a ladle (kli rishon), one would have to kasher the bowl through hagala in a kli rishon. The Tosafot rule in a similar fashion. The Rambam and the Rif, on the other hand, don’t make any mention of the need to be concerned about occasional use, and the Ran explains that this is because they rule that one may kasher a utensil based on the principle of rov tashmisho. The Rema, in his commentary on the Beit Yosef, rules that one must not rely on this principle, but rather must kasher each utensil according to even occasional use. The Shulchan Aruch rules in the opposite fashion, requiring kashering only for a utensil’s normative use. The Mishna Berura makes two interesting comments on this passage in the Shulchan Aruch. Firstly, he qualifies the ruling of the Shulchan Aruch and writes that if one knows for certain that in the last twenty-four-hour period the utensil was used in a kli rishon, one must kasher it through hagala. Secondly, he writes that although he rules like the Rema that ab initio one must do hagala on all utensils, he writes that post facto, or in the absence of a better solution, one could rely on this ruling to kasher according to normative use. Additionally, the Mishna Berura writes in his footnotes that certainly if the utensil was aino ben yomo, one could rely on rov tashmisho.
Countertops – Potential problems
When assessing the types of absorptions in the following sections, we will also need to pay attention to another factor – the quality of the absorption. As we will see in a later section, the mode or quality of the absorption, and not just the amount, will make a difference as to the way that we are able to potentially kasher that utensil.
Spills from a Kli Rishon
Among the most common of problems that can occur with regard to countertops is the problem of spills. In order to understand exactly what the issue is, we have to first understand the way that the spill happened. If the spill came directly from a kli rishon (e.g. pot, ladle, or other utensil used directly on the fire), and the spill was connected in a continuous stream to the kli rishon, then the place that the spillage occurred is considered to have absorbed through irui kli rishon – pouring from a kli rishon. In this case, the countertop would have absorbed a klipa’s worth of taste. However, if, as is likely in most cases, the stream of the spill was not continuous and was not connected to the kli rishon, then we would consider the spill to be a kli sheini. According to both the Shulchan Aruch and the Rema, a kli sheini still absorbs or causes absorption, and one must kasher such a utensil if possible; however, the quality of the absorption is that of a kli sheini, which, as we saw above, affects the kashering process.
A further, common problem is the placing of a hot, dirty pot directly on top of the work surface. The Gemara in Pesachim teaches us a principle called tita’ah gavar – if one thing is placed on top of another, the bottom object determines the status of the top object. For example, if a hot piece of meat is placed on a cold piece of meat, we say that the bottom piece “cools” the top piece. In such a case, the amount of absorption is a klipa. Obviously, the quality of absorption will depend on the object which was hot, as we’ll see shortly. This principle is brought as halacha by the Shulchan Aruch, and the Rema explains that this applies to utensils as well as food items. In light of this principle, we can understand the status of the countertops in our case – when one places a pot with pieces of food on the outside of the pot on a cool countertop, the countertop will absorb a klipa’s worth of taste, and the quality of this absorption will be that of a kli rishon which was removed from the fire. As we’ll see, this may change the method of kashering that we’re able to use on countertops.
Spills of a Solid Food
Things are even more complicated when we consider that at times one spills hot, solid food onto a countertop. In this case, in addition to the above issues which we addressed already, we must deal with a further machloket – the issue of whether or not a solid food retains heat, even in a kli sheini. Tosafot in Shabbat lay down a foundational principle throughout halacha – the idea of a kli rishon which was used on the fire and is thus hot, and a kli sheini which in and of itself is cool but is holding a hot food. Tosafot writes that a food in a kli sheini cannot cook what is placed inside of it, for it acts to cool rather than heat the food. Based on this, the Maharshal writes that since solid foods are unaffected by the walls of a vessel, the solid food retains its prior designation as having come from a kli rishon, even though it currently resides in a kli sheini. He does qualify this, however, and writes that this status of a solid food as a kli rishon is only true as regards something which is transferring its own taste. When something is transferring a forbidden taste it acquired elsewhere, or a taste which is permitted (e.g. meat or milk), the food cannot transfer taste at a level sufficient to cause it to be absorbed in the utensil on which it is resting.
The Rema brings this Maharshal but does not rule like him, instead ruling that there is a formal equivalency between a liquid and a solid as regards their status as a kli rishon or kli sheini. The Shach defends the Maharshal,but allows that at the very least one would rule like the Rema in cases where the solid food acted like a liquid in some sense, as in the case of rice.
Were we to treat solid foods as a kli rishon, we would create a new category of quality of absorption, that of something which absorbed through a kli rishon off the fire. This new type of quality of absorption might, in turn, require a new type of kashering process, a point to which we’ll return later in the essay.
Based on the principles we have laid out above, we can now begin to approach our case of countertops and try to understand the various opinions. The Beit Yosef writes in the name of Hagahot Maimoniot that there is a custom to pour boiling water on tables and countertops, since at times hot chametz falls on them, like quiche or soup. There are few conclusions to be drawn from the words of the Beit Yosef. Firstly, one can understand from what he writes that this is only a custom but not absolutely necessary. This could be for a number of reasons – firstly, as we learned above, the Shulchan Aruch is only concerned about rov tashmisho, and therefore the fact that these surfaces are only rarely used for hot chametz would mean that they don’t require hagala from the strict letter of the law. Further, the fact that he writes that these surfaces only need irui proves that he is not concerned about the distinction between a solid and liquid food.
This is indeed how the Shulchan Aruch rules with regards to tables and countertops, writing that “it is our normal practice” to pour hot water on these surfaces. The Mahari Weil, however, didn’t allow simple kashering through pouring of water on tables and countertops, since he was concerned that these surfaces were used for quiches and the like, and presumably was concerned that solid foods were to be treated differently than liquids, something that the Maharshal would echo many years later. Instead, and this is a point to which we will return, he required using a white-hot stone over which hot water was poured. This is the position of the Chok Yaakov, though he writes that according to the strict letter of the law, it would be enough to do irui, perhaps revealing that he doesn’t agree with the Mahari Weil and the Maharshal with regards to the status of solid foods. The Mishna Berura writes that ab initio one should act like the Mahari Weil, though one may rely on the Chok Yaakov to only do irui when necessary. In his footnotes there, he explains that this is because, on a minimum level, we rely on rov tashmisho, and in the case of a table or countertop, their normative use is with cold food, and therefore it would be enough to simply wash them off with cold water.
Thus far, we have established that one should, if given the opportunity, kasher one’s countertops with a white-hot stone. This is, however, based on a number of stringent assumptions – namely, that one must kosher according to even non-normative or irregular use of utensils, that one must be concerned that solid foods are considered a kli rishon, and that the particular quality of the absorption is important, an assumption we will examine in our next section.
K’bol’o Kach Polto – A Matter of Heat or Method?
The Gemara in Shabbat records a dispute between the Sages and R. Yosei about the Tiberias hot springs. The Sages consider the springs to be heated by the sun and therefore to be in a category of heat which is forbidden to cook with on a rabbinic level on Shabbat – toldot chama. R. Yosei, however, considers the springs to be heated by fire (the fires of hell) and therefore toldot ha’ur – a category of heat which is biblically forbidden to cook with on Shabbat. Based on this Gemara, the Orchot Chaim writes that one may not kasher utensils in the Tiberias hot springs, even if the utensil only requires a minimal level of kashering – that of a kli sheini, since the hot springs are not considered toldot ha’ur. From this ruling we can infer that the Orchot Chaim understood that on a fundamental level, the concept of k’bol’o kach polto requires more than simply a matching level of heat. Instead, it seems that one must match the method or quality of the absorption if one wants to kasher the utensil. This is how the Shulchan Aruch rules as well.
This opinion appears in the Tur as well in Yoreh De’ah, where he brings a machloket about the nature of k’bol’o kach polto. According to one opinion, a utensil which absorbed through use in a pot which was directly on a fire needs to be kashered in a pot which is directly on a fire – it’s not enough to simply match the temperature of the water, but rather one must match the mode of the absorption as well. The other opinion simply requires the heat of a kli rishon, regardless of whether or not the utensil is on the fire or not.
K’bol’o Kach Polto – Towards a Solution
In order to understand the nature of k’bol’o kach polto, we need to look deeper to see how the various authorities understood what was happening in the kashering process. Rashi explains that k’bol’o kach polto means that if something absorbed through a kli rishon, one would require a kli rishon to kasher it. This doesn’t seem to shed too much light on the subject, for we are still left with the question of whether or not this is required for the temperature or the mode. The Ritva explains that the need for a kli rishon is specifically for the mode of absorption, and that even though as regards Shabbat, a kli rishon off the fire is still considered a kli rishon for cooking, as regards kashering dishes one needs a facsimile of the method in which the utensil originally absorbed the taste. The Sefat Emet, in explaining the position of many authorities of his time to be stringent and require the kashering of knives through direct flame, writes that since it is impossible to recreate the exact mode in which the knives absorbed, the authorities decided to go one level more stringent to ensure the proper kashering of the knives. It seems clear from this that the Sefat Emet is endorsing the opinion that the mode of kashering is important. A similar point can be seen in the Gemara in Avoda Zara where the Gemara discusses kashering a pot which is too big to fit into any other pot. There, the Gemara says that one should make a rim of either mud or dough (depending on whether it’s for the year or Pesach) and allow the water in the pot to boil over, thus kashering the rim of the pot. The reasoning behind this, explains Rashi, is that that part of the utensil only absorbed taste through occasional splatters, and therefore ought to be capable of being kashered that way as well; however, because we can’t ensure that the splatters will go everywhere that they did before, we create an extra rim to allow the water to boil over and ensure a thorough kashering. This, too, seems to provide more evidence for the opinion that kashering must take place in the same way that the utensil originally absorbed. This is the position of the Ran as well.
The Meiri is of the opinion as well that it is the mode that makes the difference, and he proves this from a Gemara in Pesachim which discusses the death penalty of burning. There the Gemara says clearly that one must use molten lead which was melted through fire, whereas naturally occurring molten lead is not acceptable for this purpose. From this Gemara, the Meiri explains that something which is hot but not heated through fire is not considered to be fire at all, and he expands this explicitly to apply to hagala.
The Ra’ah takes the opposite stance. He is of the opinion that all that matters in the kashering process is the level of heat. It seems that on this matter, however, he is a lone opinion. Indeed, the Shulchan Aruch paskens in a number of places that the method of absorption matters as much as the temperature.
This brings us to our next inquiry – since we’ve said that we need to kasher in the same manner as the utensil absorbed, can we kosher something which was used with real fire with water boiled on a heating element? Will we consider a heating element to be fire or not?
Heating Elements and Fire
In order to decide what the status of electric heating elements will be, we must turn to other realms of halacha where the issue is discussed. We will examine the status of heating elements on Pesach, on Shabbat, and on Yom Tov, and try to come to a conclusion regarding whether or not a heating element is considered fire.
The earlier section of the Gemara in Pesachim which was quoted in the Meiri seems to prove that at least in terms of nega’im, a red hot piece of metal is not considered fire. This is the conclusion of the Meiri as well regarding the Korban Pesach, that hot metal is not considered fire in terms of roasting it. Furthermore, he seems to allow only molten lead which was heated by fire for use in the death penalty, as we discussed earlier, perhaps leaving the door open for the understanding that metal heated by things other than fire is not considered fire.
The question of whether or not a heating element will be considered as fire or not is especially important when it comes to Shabbat. The Gemara in Shabbat writes that cooking with something which was heated by fire is forbidden from the Torah, whereas cooking from the sun directly is permitted; there is an argument, however, when it comes to cooking with something that was heated from the sun. Rashi explains that the problem with cooking with something that was heated by the sun is that one will come to misinterpret what is happening and thereby cook on Shabbat in a normal manner, thus violating a biblical commandment. However, he explains that with regards to cooking from the sun, no one would misunderstand what is happening because “that’s not a normal way of cooking.” The Shulchan Aruch rules that it is forbidden to cook with something heated by the sun – toldot ha’chama – but it is permitted to cook directly from the Sun. The Ateret Tzvi explains that this is because cooking in the sun is not a normative mode of cooking.
Based on this distinction of Rashi, the Igrot Moshe writes that cooking in a microwave would take on all of the laws of cooking on fire, since it has become a normative way of cooking. Rav Binyamin Zilber agrees with the principle of the Igrot Moshe that one could theoretically extend the definition of toldot ha’ur on Shabbat to anything which is a normal mode of cooking, and this would certainly be the case with regards to electric heating elements.
In contrast, Rav Goren writes that in his opinion, a burning piece of metal is not fire, and thus cooking on it would be a rabbinic prohibition. Rav Shlomo Zalman Auerbach though disagrees with this understanding.
On Yom Tov
With regards to Yom Tov, the issue of the status of red-hot metal comes up in relation to the transference of fire. As we know, one may transfer an already existing flame on Yom Tov to another flame; one may not, however, create a new flame from scratch. The Mishna Berura, quoting the Ketav Sofer, writes that lighting a match from red-hot metal is forbidden, as this is not considered actual fire. Rav Amram Bloom, in his responsa Beit She’arim, writes that the law regarding red-hot metal’s status as fire would be dependent on the dispute between the Rambam, who holds that heating metal on Shabbat until it sparks is considered creating a new flame and thus would be fire, and the Ra’avad who holds that heating metal on Shabbat is only a matter of makeh bapatish and thus wouldn’t be considered fire. Rav Moshe Feinstein rules that in his opinion, red-hot metal would be considered fire.
It seems that according to many modern authorities, among them Rav Feinstein and Rav Auerbach, red-hot metal would be considered fire, and thus water which was heated through a heating element (provided that it actually reaches a stage where it is red-hot) would be sufficient to use in the kashering process.
Is Steam Water?
Our next task must be to understand the nature of steam – is it considered to be water, and thus able to effect a hagala on the relevant utensils, or is it not considered to be equivalent to hagala?
The Rivash writes that steam is considered to be water, and is a medium for the transference of taste. He proves this from the law of a drop of milk which falls into a pot. The Gemara writes that if one were to cover the pot, it’s as if the milk was stirred into the pot. The Rivash explains that this is because once the pot is covered, the steam serves to mix the taste in the same manner as if the pot was full until the top with liquid. This seems to be the conclusion of the Rema as well in a different case, where he rules that a drop of milk which falls on to the cover of a pot is considered as if it had fallen parallel to the liquid portion of the food, seemingly ruling that the steam filling the pot is equivalent to the liquid itself. The Maharsham uses these sources to prove that steam is considered to be water itself. Rav Moshe Feinstein, while being of the opinion that the heat of steam is not a relevant factor in the kashering process, writes that if the steam leaves behind a film of water, then the steam will work for kashering like hagala.
However, the Darkei Teshuva writes that cooking with steam would not be considered bishul akum, seemingly ruling that steam is not the same as water itself.
If we put together all that we’ve discussed thus far, including the potential problems which arise with countertops and the various opinions regarding different kashering processes, we can begin to come to a conclusion regarding the use of steam cleaners for kashering.
Even if we posit that a countertop has absorbed in a quality which would require hagala (by using it for hot, dry chametz, for example), it would seem to be that using a steam cleaner is certainly no worse than using a white-hot stone to reboil the water, and may even be preferred. If the purpose of the hot stone is to ensure that the water poured over it (or the water over which it is passed) re-boils and retains its heat level (and thus is capable of kashering), a steam machine (which is definitionally hotter than boiling water, as steam is only created above 100 degrees Celcius) would seem to be ideal, as it is more effective in maintaining a heat level which would be appropriate for kashering. Further, although the steam could potentially be considered a stream which is still connected but is not in the pot itself (as we discussed above), it would seem to be better than such a case, as the machine is designed to jettison the steam at a very high heat level and thus could potentially be considered as if it were still in the pot itself. In terms of the concern of k’bol’o kach polto, which requires the mode of the expulsion to be the same as that of the absorption (or higher), one could definitely consider the heating element inside of a steam cleaner as fire for the purposes of kashering (indeed, this principle is utilized whenever one koshers with an electric kettle). A further advantage that steam cleaners may have over the traditional white-hot stone is the ability to be more exact in the application of the hot water/steam than a stone would allow.
In summary, it seems that for kashering countertops, a steam cleaner would be an excellent choice, and may even be preferable to the traditional hot stone method.
 Numbers 31:22-23
 Babylonian Talmud, Avoda Zara 75b
 “Libun” – the exact parameters of this type of kashering are subject to discussion and are beyond the scope of this essay. We will also deal later in the essay with the exact definition of this type of kashering vis-à-vis the principle of k’bol’o kach polto.
 Rif, Pesachim 8b; Rosh, Pesachim 2:7
 O.C. 451:5
 O.C. 451:6
 A miniscule amount, equal to the first layer of a surface. Lit. “a peel’s worth”.
 Lit. “pouring”
 Babylonian Talmud, Shabbat 42b
 Shabbat 2:17
 R. Samuel ben Meir (Troyes, c. 1085 – c. 1158)
 R. Isaac ben Samuel the Elder (c. 1115 – c. 1184)
 Darkei Moshe HaKatzar, Y.D. 95:5
 For more on what is considered a primary vessel, see the section on heating elements later in the essay.
 O.C. 451:16
 Yerucham ben Meshullam (1290-1350)
 Meir HaKohen (1260 – 1298)
 O.C. 451:16
 451 s.v. “דכל כה״ג הוי הגעלה”
 Hezekiah da Silva (1659–1698)
 The exact definition of this term is disputed. According to most authorities, it means that the absorption in the vessel is more than twenty-four hours old and therefore, post facto, does not transfer forbidden taste.
 Eliezer ben Yoel HaLevi of Bonn (1140–1225); Chelek 2, Pesachim 464
 Avoda Zara 74b, s.v. “״דרש רבא נעוה ארתחו
 Hilchot Chametz U’matza 5:24
 Ran al haRif, Pesachim 8b
 Darkei Moshe Hakatzar, O.C. 451:6
 O.C. 451:6
 Sha’ar HaTziun 451:50
 לא נפסק הקילוח
 See Rema, Y.D. 92:7
 Y.D. 68
 Y.D. 92:7
 Babylonian Talmud 75b-76a
 Y.D. 105:3
 Babylonian Talmud, Shabbat 40b, s.v. “ושמע מינה כלי שני אינו מבשל”
 Solomon Luria (1510 –1573)
 Yam Shel Shlomo, Chullin 7:44
 See the Beit Meir on the Taz, Y.D. 94:14 who questions the basic premise of this qualification.
 Darkei Moshe HaKatzar, Y.D. 105:4
 Shabbatai ben Meir HaKohen (1621–1662); YD 105:8
 O.C. 451:20
 Jakob Ben Yehuda Weil (c. 1385 – c. 1457); Shut Mahari Weil 193
 Jacob ben Joseph Reischer (Bechofen) (1661–1733); O.C. 451:20
 Sha’ar HaTziun 451:144
 Aaron ben Jacob ha-Kohen (Mid-thirteenth century); Chelek 1, Hilchot Chametz U’matza, 92
 O.C. 452:5
 Y.D. 121, See Beit Yosef there as well.
 Pesachim 30b, s.v. “כבולעו כך פולטו”
 Pesachim 30b, s.v. ״ובכלי ראשון״
 Yehuda Aryeh Leib Alter (1847 – 1905); Pesachim 30b
 Avoda Zara 76b s.v. ״כך בשעת פליטה״
 Chidushei HaRan (Meyuchasim), Shabbat 40b, s.v. ״מכת מרדות דרבנן״
 Avoda Zara 75b
 Bedek HaBayit 3:3
 See O.C. 451:5, 461:1
 Skin blemishes described by the Torah, e.g. tzara’at
 Beit HaBechira 75a
 Shabbat 39a s.v. ״דשרי״
 O.C. 318:3
 Tzvi Hirsh Eichenstein (1763 – 1831); OC 318:5
 O.C. 3:52
 Shut Az Nidbiru 1:34
 Sinai, Shevat-Adar, תש״ט, page 328
 קובץ מאמרים בעניני חשמל בשבת, ״הדלקה וכיבוי אור החשמל בשבת״, עמ׳ 85
 S.A., O.C. 502:1
 Igrot Moshe, Y.D. 2:75
 Shut Rivash 255
 Y.D. 92
 Y.D. 1:60