? Will Fitting a Rebate Set Invalidate the British Standard Rating on a Mortice Lock?
Not necessarily — but it depends on the lock and the rebate set you use.
✅ When It Won’t Invalidate the BS Rating: All of these must be true.
If the rebate set is specifically designed and tested for use with the BS-rated mortice lock (e.g. BS3621 or BS8621)
Most reputable lock manufacturers (like Yale, Union, Era, etc.) sell matching rebate kits for their BS-rated mortice locks.
The use of the lock and the rebate kit have been approved by the home owner's insurance company.
⚠️ When It Could Invalidate the Rating:
If you use a non-compatible or third-party rebate kit that hasn’t been tested with the lock.
If the rebate kit alters the fitting or function of the lock in a way that affects its integrity (e.g. affects bolt throw, alignment, or door/frame engagement).
If the installation is poor, leaving the lock misaligned or insecure.
It has not been approved by the insurance company.
? Important for Fire Doors:
If the door is a fire door, using non-approved hardware, including rebate kits, can invalidate fire certification — even if the lock itself is rated.
✅ Best Practices:
Always use a rebate set supplied or approved by the lock manufacturer.
Check with the home owner's insurance company.
Consider using a multipoint French door lock kit.