How much home equity debt is too much? The answer depends on how much you owe to other creditors, whether you get a home equity loan or a line of credit, what you're using the money for and whether you have self-discipline.

As rates continue to rise, more and more homeowners will ask themselves how much they can safely borrow with a second mortgage -- either a home equity loan or an equity line of credit.

The lender is your first line of defense against taking out a loan for too much. "From a credit risk and business standpoint, the business thinks you can afford it," says Anthony Hsieh, president of HomeLoanCenter.com. "Otherwise, they wouldn't approve it for you."

A lender determines whether you can afford the loan by comparing your debt to your income. Most lender guidelines limit borrowers to total debt payments not to exceed 45 percent to 50 percent of before-tax income, says Raymond Michaud, who runs Mortgage Center of America in Trumbull, Conn.

Another ratio to think about is the size of the second mortgage compared with the first mortgage. Generally, the second mortgage shouldn't be for more than 30 percent of the first mortgage.

Another factor is the type of debt you take on. A home equity loan is a lump-sum amount. You start accumulating interest the moment you sign the loan papers. Your monthly payments repay the loan over a set period. An equity line of credit behaves more like a credit card. You don't pay interest until you draw from the credit line.

A home equity loan is better used to repay a one-time expense: consolidation of debt such as credit cards and auto loans or startup money for a business. A line of credit is better for continuing expenses, such as a lengthy home renovation or tuition or as a source of income in case of unemployment.

A line of credit "is a giant credit card that you can use to sort of manage your life," Hsieh says. "But it goes back to that one word -- discipline." If you use a line of credit to pay off your credit cards, you can't afford to run up those cards again.

Michaud delivers a final caveat: "Do understand that the loans, the lines of credit, are mortgages," he says. "People forget it all the time. It's a mortgage. It's a lien against your property."