GJ
The reason I suggested checking the down stream load is I once had a simular problem. A 4000 amp service had 14 runs of 500MCM to it. Kept burning cables. Not a good thing in an ethonal plant. We repulled the 500 MCM making sure all cables were the same length. When we turned the service back on amp readings were scary less than 200 on 2 or more cables over 600 on others with a range of readings in between. The engineers and the rest of us went nuts trying to find the problem.
While the plant was down because of this another crew did some repair of some computer controlled equipment and rebalanced the various loads at some sub panels.
After repulling the 14 runs of 500 MCM again,reterminating and checking every thing else back on the service came. Same problem different cables. Back to tests, discussion-sometime heated- meetings etc.
Other crew comletes their tasks using only enough power to test each individual subpanel.
Management want more tests full power run-- problem disappeared.!!!!!
What caused it is still an arguement something downstream probably causing a harmonic imbalance. What was never agreed to. When we left all 14 500 MCM / phase 3 phase 480 cables were within 4% of each other.
Hope you have better luck and actually find a cause.
