Wearing Tefillin On Chol HaMoed
To his honor HaRav Ratzon Arussi shlit”a,
Is it necessary according to the Rambam to put on tefillin during Chol HaMoed? And if so, in my synagogue – where they are not accustomed to wearing them – what should I do? Should I put them on in the synagogue with everyone, even though I am the only one who wears them? Or should I perhaps put them on at home? (Or should I not put them on at all?)
The Rambam does not write explicitly that it is either permitted or forbidden. Mori (Rabbi Yosef Kapach z”l) is of the opinion that the Rambam rules like the ancient Torah scholars of Spain who held that one does not wear tefillin on Chol HaMoed, and his words appear to indicate this. And so shev ve-al taaseh adif , but you should certainly not put them on in a synagogue where they do not wear them on Chol HaMoed.
 There is a principle that when a doubt arises as to whether one is obligated to perform a mitzvat aseh or not, it is better to refrain from taking any action than it is to perform an action that one should not. Thus, in such a case shev ve-al taaseh adif, or "to sit and do nothing is preferable."