ECN Forum Forums General Topics of the Trade General Discussion Area Engineering Supervision

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?

probably with some long winded explanation of natural grey....

The engineering supervision exception allows parallel neutrals for a wire size smaller than the usual 1/0 minimum for parallelled conductors. It does not allow for increased condiut fill. An additional #2 THW in this conduit will exceed the allowable fill. 1 1/4" conduit allows .598 sq.in. fill. It currently is filled to .533 sq.in., and therefore maxed out for #2. This is a good example of someone following the minimum code requirements. 1 1/2" conduit would of been easier on the pull, also. But, hindsight is 20-20, and I can't say I blame the installer.
Is this a theoretical, or real instance?

Sparky:

Yes, I agree, you are probably correct, and the new 2002 NEC removes the word "natural" wherever it described the grounded conductor.

Redsy:

Just a scenario, and yours was a good reply -- and the first one that gives us a good reason to be concerned about "who" does the supervising!

Also, Chapter 9, Table C1 on page 585 in the 1999 NEC shows where only 4 THW are allowed in the 1-1/4 inch EMT, and where 6 are allowed in the 1-1/2 inch EMT.

There would not be this 'engineering conflict' to simply upsize the noodle....

Better yet, there would be little concern if it were in fact fed via 1 ph.

Joe brings up a good question. What constitutes "Engineering Supervision"?

Every project I work on here at work is under the direction of a Registered Professional Engineer. I call that engineering supervision. However, if I were out there pulling wires, etc. as some of you are, then what is engineering supervision? Inspectors aren't required to be Registered Engineers in this state, perhaps in other states. As a field person, do you need to hire an engineer when necessary? How do you confirm that you have done so? Does the engineer sign off on something?

Just a few questions that come to mind.

As a daytime employee of a chemical plant, I report directly to a chemical engineer. I have never used the "Engineering Supervision" clause, and the assumption could be made that an E.E. is required. However, chemical engineering seems to encompass many physical disciplines, and I have discussed many electrical & code issues with him.