The Sodium percarbonate in aqueous solution produces produces Sodium Carbonate and Hydrogen Peroxide.
[Na2CO3]2 + 3 H2O = 2Na2CO3 + 3 H2O2
The Peroxide acts as a bleaching agent. The Sodium Carbonate Produced increases the pH of the solution to stabalise the Hydrogen Peroxide so that it remains in solution to do its work, (rather than breaking down into oxygen and being released)
The Sodium Tripolyphosphate is stain remover and degreaser
The Sodium Tripolyphosphate is a builder and is used to improe the effectiveness of soaps and cleaners.
Other cleaners also use
Sodium Tetraborate (Borax) Na2B4O7.10H2O - A Detergent
Sodium Perborate NaBO3.H2O - Bleaching / Active Oxygen
To make your own cleaner I think you'll need 3 components...
3)Buffer / Stabiliser
As far as using straight sulfamic acid, I'd like to know what the other 85% of ingredients are first, to see whats going on.
Most Commercial Descalers use Sulfamic Acid, Maleic Acid and Citric Acid, you can use cirtic acid by itself in solution as a descaler in commercial and domestic machines with no problems, its non-toxic and you can taste it so you know when its all flushed from the system.