One person cannot be culpable for the failure of a test program to verify this equipment would function as intended. Testing is baked into the engineered procedures to design and install this system, and their work controls dictate that they be reviewed and approved. It's obvious you know little regarding electrical distribution and protection, in addition to not rtfa.
He or she is culpable if they put the wrong values in for the operating parameters. If this had gone the other way and caused a fire or worse, then there would be criminal negligence charges. Engineers get paid to do the job correctly. Where safety is at sake, they shouldn't be putting their name on something unless it has been properly verified. I can understand an engineer wanting to be conservative in these values so that a problem will tend to be a false positive rather than a failed safety, but it doesn't change the fact that there is a narrow "correct" range for these operating values that will allow the device to operate correctly without causing false positives. The fact that the values were not within that range indicates that the responsible engineer did not know what that range was, and consequently had not done his/her job.