Data centre for a telco. Needs No-break installed. Generator shed gets built, stonking big diesel genny gets carted in and the guys from Perkins (or whoever manufactured that beast) gets the thing chugging. They listen, probe, do a few adjustments, listen some more, consider it Fine, let it run some more and figure it's time to push the Engine Stop button, sign off on the job and hand it over to the sparkies to let them do their bit. Alas, the Engine Stop button didn't., as it apparently wasn't yet hooked up. "OK, maybe it's that other button".
That didnt't stop the engine either, but it did stop the computer room.