Poor Leadership

I was appointed as an Mechanical and Electrical Manager to several upgrading and renovation works.   The M&E works were the air conditioning and mechanical ventilation (ACMV), electrical distribution, uninterruptible power system and generator.  
We engaged external Mechanical and Electrical Consultants to design and draft the specifications.
All works were tendered out and awarded to the lowest tenderers that comprised to the design and specifications.
I was assisted by an Engineer and a Technical Officer in the coordination, testing and commissioning of all the M&E system.
During the last December School holiday, I approved both their annual leaves, about two weeks.
I pull in my maintenance team, a Senior Technical Officer to cover the project works.
My Senior Technical Officer recommended a variation order to modify the electrical protection system that was necessary to prevent a nuisance tripping due to surging of current.   The recommendation was supported as it makes logical sense.
About a month later, the contractor hand over the renovated premise.   Testing and commissioning were carried out and no sign of defect was noted.
The entire Mechanical and Electrical system went live the following week.   My Engineer, Technical Officer and myself attended the opening ceremony.
Half way through the ceremony, we experienced power tripping in some equipment.   We investigated and it was caused trigger by a spill drink on an equipment.   However, the tripping caused more than ten percent of the equipment to trip, which was abnormal.  
My team immediate ran thru the entire electrical protection system.   We discovered, there an over design of protection system that was approved by me a month ago.
We immediately bypass the protection system and were able to supply power back to the equipment.  
The tripping was a bad experience it was an official opening ceremony where all the bosses attended.  
What cause the over design was due to change of design was not...