JCT and NEC4 aren't interchangeable — they're built around different philosophies of who manages risk and when.
JCT is more traditional: clearer allocation of risk at the outset, familiar mechanisms for extensions of time and loss and expense, and widely understood by contractors and subcontractors across the market. NEC4 is built around active, collaborative risk management through early warnings and compensation events — better suited to projects where scope or conditions are likely to change as the work progresses.
Neither is inherently better. The wrong one for the project, though, tends to generate more disputes than either would on its own.
