Long-lead item
A component whose manufacturing lead time is long enough to set the schedule of the project that needs it.
A long-lead item is a component that has to be ordered far ahead of the work it belongs to, because the time to make it exceeds the time available once construction starts. In large infrastructure these are typically heavy forgings, pressure vessels, large power transformers, switchgear and similar items made by a small number of qualified plants.
They matter disproportionately because they are where scarcity concentrates. A component with three qualified producers worldwide is a schedule risk before it is a cost risk, and the useful question is not who could make it but who is qualified to make it and has capacity in the window the project needs - which is usually a sole source question in disguise.
The category expanded recently rather than changing in nature. Transformers and switchgear became long-lead items when data center demand arrived at plants sized for grid replacement work, which is a demand shock rather than a manufacturing failure - and it is why a compute schedule and an energy schedule now share the same constraint.
Evidence that keeps pace with the decision.
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