The Abudirham’s Siddur was first published in Lisbon, Kislev 22, 1489. There are three things that if placed above 20 Amot – cubits – are not-kosher: 1) An Eruv, 2) Chanukah candles, and 3) a Succah.
Each is hinted to in a verse: “They have come for shelter under my roof,” (Genesis 19:8) hints at Eruv. The Eruv must be placed where it can offer shade, which is at a maximum height of less than 20 Amot.
“And there will be a Succah as a shade from heat in the daytime,” (Isaiah 4:6) the Succah, too, must not be so high that it does not offer shade.
“This was the dedication of the Altar, on the day,” – biyom – which counts as B Y V M, or the number Twenty. (Abudirham: The Order For Lighting The Chanukah Candles)
Can you find the connection between the three laws?