In this article, I mentioned that a small change in the later stages of the project execution has a massive impact in cost and schedule. Another good example is what I am going to tell you.
A cable length of more than 200 meters is not unusual in the hydrocarbon or mining industry. A cable about this lentgh is used to supply the a distillate shipping pump rated abou 600kW. The pump area is basically Zone 2 as it enclosed, naturally ventilated.
The project requirement is more stringent that usual, the safety margins are much higher than what is required by the standards. Steady-state volage drop for motors is only 2%. Standards requirements are higher than that.
Cable sizing was done. Cables and the pump were purchased and delivered to site.
During the installation, the construction crew noticed that the cable entry and terminals of the motor were 1-size smaller than the cable. It might have been an oversight by the equipment package engineer.
Modification of the motor terminal is not an option as it will invalidate that certification of the motor. Replacing the cable with a smaller size would not meet the project design basis requirement. The only solution, install a certified junction box between the motor control center and the motor.
The 200 m cable will be terminated at the junction box, then a smaller size cable suitable for the motor cable box will be installed between the junction box and the motor. The solution is easy (that was what the construction crew said). I agreed with them as they were only looking at one perspective of the issue. If taken at a different perspective, it is a different story. That is what we need to analyze.
Looking at the whole picture of the modification, there are 4 x 600kW shipping pumps affected. The modification required 4 additional tag numbers for junction boxes and 4 tag numbers for the cable between the junction box and the motors. That was a total of 16 new tag numbers.
This change has affected about a hundred drawings and documents. Drawings redrawn, documents updated, went for quality check, to document control before it ws finally issued for construction.
The process took almost a month to implement. This has delayed the commissioning and completion of the project. It was only due to an small oversight.