Siman 411
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א מִי שֶׁהָיָה בַּמִּזְרָח וּבֵיתוֹ בַּשָּׂדֶה וְאָמַר לִשְׁלוּחוֹ לְעָרֵב לוֹ בַּמַּעֲרָב, אִם נָתַן הָעֵרוּב מֵהָלְאָה לְבֵיתוֹ בְּעִנְיָן שֶׁהוּא רָחוֹק מִמֶּנּוּ יוֹתֵר מֵאַלְפַּיִם וּבֵיתוֹ קָרוֹב לוֹ בְּתוֹךְ אַלְפַּיִם, הָעֵרוּב אֵינוֹ כְּלוּם וְנִשְׁאַר לוֹ שְׁבִיתַת בֵּיתוֹ. נָתַן הָעֵרוּב בְּעִנְיָן שֶׁהוּא לוֹ בְּתוֹךְ אַלְפַּיִם, אַף עַל פִּי שֶׁגַּם בֵּיתוֹ לוֹ בְּתוֹךְ אַלְפַּיִם, קָנָה שְׁבִיתָה בִּמְקוֹם עֵרוּבוֹ וְלֹא בְּבֵיתוֹ.
1 One whose home is in the east and he placed the eruv in the west. Contains 1 section One who is in the east with his home in the field, and told his agent to make an eruv for him in the west — if the agent placed the eruv beyond his home such that it is more than two thousand cubits from him and his home is closer to him within two thousand cubits, the eruv is void and he retains the Shabbat rest of his home. If the agent placed the eruv such that it is within two thousand cubits of him — even though his home is also within two thousand cubits of him — he acquires Shabbat rest at the place of his eruv and not at his home.