NEC3 ECC: Can delay damages be applied to Key Dates?

No - delay damages under X7 are applicable to sectional completions if you have them (under X5) and the overall Completion Date. Key Dates are separate and if you have them identified within contract data 1 then the liability if the Contractor misses this date is what ever cost the Employer incurs under clause 25.3. This could be minimal cost or very significant cost and potentially worse than delay damages depending on the ramifications.

Employers should only introduce them where they really need them to manage a 3rd party interface (as the Contractor will now price associated risk) and the Contractor needs to manage them very closely on the programme.