Came into work this morning, and none of the imacs would power on.
Tested the electricity trunking, all fine. It turned out they all needed the power cutting for 10 seconds, then they'd power on fine after that.
Would a power spike cause that?
They were all asleep and you didn't give them enough time to 'wake'?
Your wiring is faulty and not enough power was being received to power the machines after they had shut down due to perhaps a power cut, when you reset the power it supplied the correct load. Check your wiring for faults?
Thats my best guesses
It's too much load powering all on at once.
When we do computer rooms you need to install a breaker to take a large start up current.
They definately weren't asleep..... I've been looking after macs for a long long time.
Wiring is fine, we've had an electirican out to check it all...
Im guessing there was a power spike over the weekend.
I'd reset the SMC. To make things easier, can the OP stagger the time the Macs come on? This way, the initial inrush of everything starting (inrush current to spin up HDDs and fans) isn't hitting the circuit all at once.