The normal balance for an account is determined when you specify an Account Type for the account in General Ledger (Setup, Accounts, General tab).
The normal balance for Asset and Expense accounts is a debit. Debit amounts for these accounts print as positive amounts on the statement. Credit amounts for these accounts are considered abnormal amounts.
The normal balance for Liability, Equity, Income and Retained Earnings accounts is a credit, which is stored as a negative number. Credit amounts for these accounts print as positive amounts on the statement. Debit amounts for these accounts are considered abnormal amounts.