In a well-known comedy routine, a well-known comedian reenacts Hashem’s instructing Noah to build the ark. Hashem instructs Noah to build the ark three hundred cubits (Amot) long, fifty cubits wide and thirty cubits high. At this point, the comedian portrays an incredulous Noah asking God, “What’s a Cubit?” The celebrity likely did not realize it, but he raised an issue that is vigorously debated among Posekim regarding which a significant difference exists between Sephardic and Ashkenazic traditions. This has important ramifications for building community Eruvin. Eruv creators should bear the Sephardic standard in mind to ensure that the Eruv satisfies Sephardic, as well as Ashkenazic, customs. This has a specific application in regards to a recurring issue in most Eruvin, namely gaps of up to ten Amot. The question becomes, as the comedian said, “What’s a cubit (Amah)?” How much of a gap in terms of feet and inches may be tolerated?
Gaps of Ten Amot
Unlike the making of an Eruv in the Jewish State, where we are at home and government authorities are supportive, outside of Eretz Yisrael, especially in smaller Jewish communities, Eruvin must be made in the least intrusive manner as possible. Every effort should be made to use existing structures such as utility poles (especially those with a wire running on top of the pole), steep slopes and fences. In such situations, gaps will often exist when seeking to transfer from fences, poles, steep slopes, etc. The Halachah tolerates a gap of up to ten Amot in such circumstances (see Mishnah Eruvin 1:1, Shulchan Aruch O.C 362:9 and Aruch HaShulchan O.H. 362:30 and 36 and 363:45).
Another measurement of major importance is the Tefach (handbreadth). Walls are required to be at least ten Tefachim high to be used as part of an Eruv (Mishnah, Eruvin 1:9 and Shulchan Aruch O.C. 345:2). Thus, when constructing an Eruv, one must specifically define two essential measurements: ten Amot and ten Tefachim (there are six Tefachim in an Amah).
What’s a Cubit? What’s a Tefach? – Chazon Ish, Rav Moshe Feinstein and Rav Avraham Haim Na’eh
Twentieth century Posekim intensely debate the equivalent of an Amah and a Tefach in contemporary terms. The very wide range of opinions on this matter is summarized in the Encyclopedia Talmudit (the entry “Amah”). The three primary opinions are that of the Chazon Ish, Rav Moshe Feinstein and Rav Avraham Chaim Na’eh. The Chazon Ish and Rav Na’eh were contemporaries living in Eretz Yisrael and engaged in vigorous debate about this topic from 5703/1943 until 5713/1953, the year in which both of these sages passed to the next world. Rav Moshe Feinstein issued his ruling on this issue in 1956 when he lived in the United States independent of and without relating to the debate between the Chazon Ish and Rav Na’eh.
Their opinions are as follows: According to Rav Moshe Feinstein (Teshuvot Igrot Moshe O.H. 1:136), an Amah is 21.25 inches (53.98 centimeters) and a Tefach is 3.54 inches (9.00 centimeters). According to Rav Avraham Chaim Na’eh (in his famous work on the topic of Shiurim, Shiurei Torah 3:25), an Amah is 18.90 inches (48 centimeters) and a Tefach is 3.15 inches (8 centimeters). According to the Chazon Ish (Chazon Ish to O.C. number 39), an Amah is 24 inches (60.96 centimeters) and a Tefach is 4 inches (10.16 centimeters).
Whose Opinion is Followed? – Sepharadic and Ashkenazic Practice
Ashkenazim and Sephardic Posekim resolve this issue differently. In Eretz Yisrael (as reported in The Laws of an Eruv, page 264, and Techumin 32:413), the custom among Ashkenazic authorities is to apply the stringencies resulting both from the Chazon Ish’s and Rav Avraham Chaim Na’eh’s opinion. Thus, they will require a fence to be forty inches high but would not permit a gap greater than fifteen feet and nine inches. In the United States, both Rav Herschel Schachter and Rav Mordechai Willig follow Rav Moshe’s ruling in Teshuvot Igrot Moshe, and they require a fence to be thirty-six inches high and permit a gap of up to seventeen feet and eight and a half inches. The Laws of an Eruv (p.264) reports that “many Posekim” in the United States adopt a similar approach.
Sepharadim, however, follow the opinion of Rav Avraham Chaim Na’eh (Rav Avraham HaDa’yah cited by Rav Avraham Chaim Na’eh in the introduction to his work Shiur Mikveh and Yalkut Yosef in many places including O.C. 550, where he rules that it is sufficient for Hadassim and Aravot to be three Tefachim long according to the size of Rav Avraham Chaim Na’eh).
Creating an Eruv Acceptable for Sephardic Jews
There is no problem for Sepharadim to rely on Eruvin created by Ashkenazic Rabbanim in Eretz Yisrael since they accommodate the opinion of Rav Na’eh when it results in a strict effect. Thus, it is not surprising to find numerous places in Yalkut Yosef (such as O.H. 584, Hanhagot Rosh HaShanah number 2) where reliance on the community Eruv is permitted without any provisos that the Eruv conform to Sephardic standards. Rav Ovadiah Yosef finds it acceptable for Sepharadim to rely upon Eruvin built according to Ashkenazic specifications without adjustments to accommodate Sepharadim.
However, this might not apply to Eruvin created in the United States under the auspices of Ashkenazic Rabbanim. Since many of the Eruvin in our country do not accommodate the stringent result of Rav Na’eh’s measurements, it would seem improper for a Sephardic Jew to rely upon such Eruvin, unless the Eruv conforms to Rav Na’eh’s measurements (i.e. all gaps do not exceed 15 feet and nine inches).
Thus, any community that has a functioning Sephardic Kehillah should endeavor to comply with Rav Na’eh’s measurements and ensure that gaps do not exceed 15 feet and nine inches. As the Rav HaMachshir of the Englewood Eruv (which has a Sephardic Minyan at a local Ashkenazic synagogue), I ensure that the Eruv conforms not only to Rav Moshe’s measurements, but also to those of Rav Avraham Chaim Na’eh. The four Rabbanim who oversee the Teaneck Eruv, Rav Lawrence Rothwachs, Rav Zvi Sobolofsky, Rav Michael Taubes and this author similarly ensure that there are no gaps wider than fifteen feet and nine inches in the Teaneck Eruv.
Other reasons to accommodate Rav Na’eh’s stringent result include the fact that Chabad affiliated Jews follow the opinion of Rav Avraham Chaim Na’eh. Thus, if an Eruv includes a Chabad community, it behooves the broader community leaders to ensure that there should be no gaps in the Eruv wider than fifteen feet and nine inches. Another reason to adopt this standard is the Shiur of the Haddasim that are mostly sold in the United States. In this author’s experience, the only two options that are sold in this country are either the Hadassim that conform to Rav Na’eh’s opinion (they are Meshulash – all three leaves are on the same level – on a majority of the rows of three Tefachim, at least 9.45 inches, of the Hadassim) or those that conform to the Shiur of the Chazon Ish, at least 12 inches. Many, if not most, of the members of many Orthodox synagogues nationwide rely upon Rav Na’eh’s view in a lenient direction regarding the fulfillment of the Torah obligation to take Hadassim on the first day of Sukkot.
Thus, if all or most of a community relies upon Rav Na’eh’s opinion in a lenient direction regarding the fulfillment of a Torah obligation, then it seems logical that Rav Na’eh’s opinion should be accommodated in a strict direction regarding the community Eruvin, even in a completely Ashkenazic community.
I presented these arguments to Rav Mordechai Willig and he responded that he makes every effort to ensure that the Riverdale Eruv (the Eruv he supervises) satisfies Rav Na’eh’s opinion when it results in a stringent direction. Rav Willig , though, proceeded to defend those communities whose Eruvin do not satisfy Rav Na’eh’s point of view but only that of Rav Moshe. He argues that since the situation involves two converging rabbinic laws (Trei DeRabbanan), there is room to adopt the lenient approach. The first is that the prohibition to carry in an area which is suitable for an Eruv (consisting significantly of Tzurot HaPetah, such as almost all citywide Eruvin today) constitutes only a rabbinic prohibition, and the second is that a gap of more than ten Amot (but there is “Omeid Merubah Al HaParutz,” meaning that a majority of that side of the Eruv is enclosed) constitutes only a rabbinic prohibition (Teshuvot Achi’ezer 4:8; the Chazon Ish, cited ad loc. and O.H. 107:5-7; and Rav Moshe Feinstein Teshuvot Igrot Moshe O.H. 2:90).
Ashkenazic Eruv planners should bear in mind Sephardic and Lubavitch Pesak Halachah and accommodate Rav Na’eh’s opinion when it results in stringency. This is especially the case since there are compelling reasons that even Ashkenazim should now be sure to accommodate the opinion of Rav Na’eh. If this is impossible to achieve or if no effort was made to confirm to Rav Na’eh’s approach, a Sephardic Jew may nonetheless utilize the Eruv.
 Regarding whether Sepharadim may use citywide Eruvin, see Rav Ovadia Yosef’s lengthy discussion in Teshuvot Yabia Omer (9:O.H. 33), where he rules that a Sephardic Jew may rely on a conventional citywide Eruv that consists primarily of Tzurat HaPetah, but that a blessing should be bestowed upon one who adopts the strict opinion. He permits, though, one who wishes to follow the strict opinion to ask another who follows the lenient opinion to carry for him.
 Golf course fences are often ideal for being a part of Eruvin since they usually extend for many miles. Many communities, including Englewood, Tenafly, West Hartford and West Orange, make extensive use of golf course fences. Rav Zvi Lieberman of London, England, told me that unlike in the United States, British law requires railroad companies to construct fences alongside the tracks. He told me that this is very helpful in creating community Eruvin in England. Security fences in Jewish communities in Yehudah and Shomeron, as well as in army posts, dramatically simplify the creation of Eruvin in those communities.
 See though, Mishnah Berurah (362:59, 363:23 and 111). Rav Mordechai Willig, whose standards are followed in many citywide Eruvin nationwide, rules in accordance with the Aruch HaShulchan. There is no reason, to my knowledge, why Sepharadim cannot rely on this as well.
 The Chazon Ish lived in Bnei Brak, while Rav Na’eh lived in Yerushalayim.
 See Teshuvot Igrot Moshe Yoreh Dei’ah 3:66:1, where Rav Moshe expresses astonishment over the existence of this debate which is based on analysis of the Gemara and its commentaries. Rav Moshe explained that the issue needs to be resolved simply by engaging in empirical measurement of an Etzba (finger; there are four Etzba’ot in a Tefach and six Tefachim in an Amah) and multiplying by four and then six in order to arrive at a definition of a Tefach and an Amah in terms of feet and inches.
 It makes sense for them to follow Rav Moshe’s ruling, not only because he was the leading Halachic authority in the United States, but also since his ruling is the result of empirical evidence gleaned from measuring the finger sizes of average individuals who reside in this country. In addition, the Aruch HaShulchan (O.C. 358:3) and Rav Ya’akov Kaminetzky (cited in The Laws of an Eruv, p. 262) present an almost identical ruling to that of Rav Moshe.
 Rav Shimon Eider cites in his Halachos of the Eruv that Rav Moshe told him to require a fence used in an Eruv to be at least forty inches high.
 See, however, Rav Feivel Cohen of Flatbush, who writes (Milu’im to Badei HaShulchan Hilchot Niddah; published at the end of Badei HaShulchan to Hilchot Basar VeChalav): “It appears that the custom is to accommodate the strict results of both the Chazon Ish and Rav Avraham Chaim Na’eh.” Rav Moshe Faskowitz told me that when he created the Eruv in Canarsie, Brooklyn, many years ago, he accommodated the stringent results of both the Chazon Ish’s and Rav Avraham Chaim Na’eh’s rulings. Rav Faskowitz informed me that the Poseik for this Eruv was Rav Gavriel Zinner, the renowned author of Neta’ei Gavriel.
 Yalkut Yosef notes that some rule strictly in accordance with the Chazon Ish, but he adds that according to baseline Halachah, this is not necessary.
 For a discussion of what areas in which it is prohibited to carry only on a rabbinic level, see Gray Matter 1:168-180.
 See, though, Teshuvot Mishkenot Ya’akov O.H. 121, who asserts that a breach of more than ten Amot constitutes a Torah level disqualification.
 May one rely on Rav Na’eh’s opinion in a lenient direction (such as relying on a wall that is only thirty two inches high) in a difficult situation? Rav Willig felt this to be permissible in a case of great need, and Rav Schachter ruled that it is not permissible even in case of great need, since he felt that it is inappropriate to rule leniently against Rav Moshe, the most prominent Poseik of the United States, especially since very often Rav Moshe adopted a lenient approach. This question depends to a certain extent on whether one applies the Gemara’s principle of “Halachah KeDivrei HaMeikeil BeEiruv” (the Halachah follows the lenient opinion regarding an Eruv; Eruvin 46a) to all aspects of Eruvin (Rosh Eruvin 2:4 and Biur HaGra O.H. 358:5) or only to Eruv Chatzeirot (Teshuvot HaRashba 5:202, Ritva Eruvin 80b and Teshuvot Igrot Moshe 2:202).
 Rav Yechezkeil Feiglin authored an essay that appears in Techumin 32:413-421, in which he argues that archaeological and other scientific evidence supports the opinion of Rav Avraham Chaim Na’eh.