Like many other grammar arguments, determining whether to use “personal” or “personnel” all comes down to the definition of each word. Once you know the definitions, you can use these words properly, even though they may look very similar.
The term “personal” refers to closeness and relates to your body or person. Somebody could be a personal friend, which means that they are more than just a casual acquaintance and are close to you.
Elizabeth is a personal friend of mine.
“Personnel” is entirely different. This term often refers to a group of people, and is usually used when referring to the military or a company. Another way in which “personnel” is used is when you are describing a specific department that manages the employees of a company. You should keep in mind that “personnel” is both singular and plural. In the plural sense, “personnel” refers to people. In the singular sense, it’s a replacement for the term “staff.”
Plural: Personnel are allowed to wear jeans on Fridays.
Singular: The studio’s personnel is expected to be reduced by layoffs.
One quick tip you can remember is that “personal” has only one “n” and refers to one person. “Personnel” uses “n” twice and refers to several people.