Getting approved for a 2nd mortgage requires the borrower to demonstrate their ability to make the monthly payments for the lender to take a risk and extend funds for a home equity loan. Most lenders will require a good credit score, above 700 to meet the 2nd mortgage qualification criteria. Since the default ratio is higher on 2nd loans, loan companies will require high credit scores. Borrowers will also need mortgage insurance if they are unable to get a purchase money 2nd mortgage.
If you already own a home and want to get a 2nd mortgage because they need cash but would rather not touch their existing loan, then most lenders will require 20% equity in their home after the new loan. In loan officer terms that means 80% combined loan to value.