To understand non convertible debentures (NCD), it would be a good idea to understand convertible debentures first. As the name says convertible debentures are those debentures which are converted to normal equity shares after a specified term. Till that time these debentures earn regular income in form for interest but once they are converted to equity shares, they are just like normal shares.
Hence non convertible debentures (NCD's) are those debentures which are not convertible to equity shares. NCD in India more or less work like company fixed deposit, where you are lending a company to get some interest income and your money back after few years. You need to check the rating of that bond. Such debt bonds are normally rated by credit rating agencies like CRISIL. A good rating indicates reasonable assurance of safety and return of principal as well as interest.
Secured Non convertible Debentures (NCD) are backed up by some assets which can be liquidated for paying off the bond holders incase something goes wrong. For this reason, the returns on secured NCDs are lower than unsecured NCDs.
Unsecured Non convertible Debentures (NCD) are the ones which are not backed by any assets and incase company is in financial crunch, there can be an issue in paying back the bond holders. Only after the payment is made to every entity which has some security, the unsecured NCD bond holders have any chance of getting back their money. So that’s the reason why these NCD’s have high interest rates.