Hi 

What is the difference between a bs5839-1 L1 system and a Grade A: LD1 system? 

None. 

The equipment is identical, the main differences are the design criteria:

- Audibility: Different requirements, e.g. Part 1 requires 75dB at the bed head of a bedroom, Part 6 only requires 85dB at the open bedroom door

- Warning for the hearing impaired: Again different requirements, more detailed and stricter in part 1

- Manual Call points: Differing requirements for call point location, not always required and different location requirements in Part 6

- Capacity of standby batteries: Generally greater for Part 6 systems (72 hours instead of 24 hours)

- Radio linked systems: Different requirements (largely similar though)