If I work for 2 differentcompanies with the same common ownership, amI entitled to overtime ifI work a combined over 40 hours a week?

The answer is, "it depends." It depends upon whether you are 1) more or less doing the same or similar job for both companies and 2) whether the companies are, despite being nominally being separate, fundamentally the same. While there is no clear line about when you might be entitled to overtime in this situation or not, the following examples may help:

1) A holding company owns a local car dealership and a fast food restaurant; you are a receptionist for the car dealership and an assistant manager (or cashier) for the restaurant. The two businesses are entirely separate; you do different jobs for each; therefore, the fact of their common ownershp does not result in the two, otherwise completely separate, jobs being counted as one for overtime purposes.

2) A company has a real estate development company (buys, rehabs, sells, etc. houses) and also a property management business (runs apartment buildings on behalf of the owners). You provide bookkeeping and administration for both. You are doing the same job for two closely related businesses that could easily be one buiness; in that case, the fact that the owners chose to incorporate the businesses separately does not allow them to escape paying you overtime when your total hours for the combined job exceed 40 in a week.

Therefore, there are situations where you would have to be paid overtime when the combined hours exceed 40, and circumstances where you would not. If you are unsure, or think perhaps you are owed overtime, consult with an employment law attorney to evaluate the situation and your rights.