The nomencl package has a different purpose than what you're using it for.
The package's purpose is to write a list of symbols or abbreviation used, with a reference to the place where they're defined or first used (at the user's choice). So it's not meant to place multiple reference to a nomenclature.
For acronyms the best package around is glossaries, but the simpler acronym is often used.
My advice is to get rid of nomencl package and use glossaries at its full power. I assume that the sense of this question is to have both a list of equations and a glossary in the document, whatever tool is used.
In fact, with glossaries, one can define as many glossaries as he wants: a simple glossary, a list of acronyms, a list of symbols and so on.
Instead of using the nomencl package, you can define a new glossary (I know the name is misleading, but that's how lists of terms are referred to in the package documentation; you can name your list as you prefer) with the following command:
\newglossary{equations}{equ}{eqn}{List of Equations}
where: equations is the type of the glossary entry, in order to distinguish it from an ordinary glossary entry; equ and eqn are file extensions for auxiliary files; List of Equations is the title of your list, as it will be printed in the table of contents and in the text.
To define an entry to be added to this list, use the glossaries command:
\newglossaryentry{sml}{type=equations,name={$\nabla B = 0$},description={Second Maxwell's Law}}
Note the value assigned to the key: type=equations; if you don't specify it, it will be added to the main glossary.
To have the glossaries printed, you have to put \printglossaries in your document backmatter/frontmatter, and run makeglossaries from command line on your root .tex file.
Best Answer
The
nomenclpackage needs some typeset text in the document -- otherwise it won't write thefoo.nlofile (if the document is called foo.tex).After the
foo.nloexists, it's necessary to use (in terminal or in an editor 'external utilities' command.)The
nomencl.istis provided by thenomenclpackage already.