NEC ECC: Option C ambiguity in works information

Under an option C contract, in the scenario where the Works Info required a piece of equipment to a particular spec and it has become apparent that the contractors works information for his design is a much lower spec. The employer requires the height spec equipment.

Who is responsible for the uplift in cost for the required equipment spec?

This is an ambiguity created by the Contractor so this would be an instruction to change the Works Information that would NOT be a compensation event and hence Contractor risk. By accepting the design, they are not taking on liability of the submission not complying with the original Works Information. In reality under option C - this would not be a disallowed cost, so the Parties would share the cost of this error (but the target will not change).