OK here's the question:
Existing raceway with 4 wires and grounded conductor is suffering because of high harmonic neutral currents.
How does the engineer apply the following exception to 310.4
Exception No. 4: Under engineering supervision, grounded neutral conductors in sizes 2 AWG and larger shall be permitted to be run in parallel for existing installations.
FPN:Exception No. 4 can be used to alleviate overheating of neutral conductors in existing installations due to high content of triplen harmonic currents.
