Discussion:

1999 NEC, Section 310-4, Exception No. 4: Under engineering supervision,
grounded neutral conductors in sizes No. 2 and larger shall be permitted to be run in
parallel for existing installations.

FPN: Exception No. 4 can be utilized to alleviate overheating of neutral conductors in
existing installations due to high content of triplen harmonic currents.

This Question is for any engineer who can give the steps needed to accomplish Code
compliance:

Please give the answer to a situation where an existing EMT, using 4 #2 AWG THW
Copper conductors will require a larger neutral, such as another #2 AWG THW added
to make 5 wires in an existing 1-1/4 inch EMT.

How will your supervision be applied to this type of installation?


Joe Tedesco, NEC Consultant