What is the difference between JCT and NEC?

The practical difference is when things get decided. JCT and NEC are the two main families of ready made construction contract, and they handle change and money in opposite directions. JCT works after the fact: the work proceeds, then valuations and certificates follow, a certificate being a formal statement from the contract administrator confirming how much is due or that a stage is complete, and disagreements are often argued out after the event. NEC works in advance: extra time or cost is handled through compensation events, the NEC name for anything that entitles you to more money or time, each notified, quoted and agreed as it arises, priced against a programme, the live project timetable, kept updated. Depending on the edition and any amendments, its notification deadlines can act as time bars, so a late notice can reduce or wipe out your entitlement. Neither family is safer in the abstract: a JCT job punishes weak records at the final account, an NEC job punishes slow paperwork week by week. What decides your risk is rarely the logo on the cover, it is the schedule of amendments behind it.

Picture the same groundworks firm running two jobs at once. On the JCT job they hit unexpected rock and press on, keeping loose records, planning to argue the extra cost at the final account months later; thin records leave them fighting to prove what the delay cost. On the NEC job the same rock is a compensation event that must be notified within a set number of weeks and quoted against the live programme; miss that window and, depending on the edition and any amendments, the entitlement can be reduced or lost entirely. Same contractor, same rock, two different disciplines: the JCT job rewards good records at the end, the NEC job rewards fast paperwork in the moment. The cover told them little; the machinery inside told them everything.