What is the difference between single cable flame tests and bunched cable flame tests?

A single cable flame test checks how one cable behaves when exposed to flame.
A bunched cable flame test checks how a group of cables behaves when installed together vertically or in cable trays.
This is important because cables installed in groups create a larger fire load. A cable that performs well alone may behave differently when many cables are bundled together.
For cable trays, risers, electrical rooms, and industrial routes, bunched flame performance is often more relevant than single wire flame performance.