The foreman for a group of electricians wiring an industrial facility sent me an e-mail asking a number of installation questions based on the National Electrical Code (NEC). According to the foreman, the engineering firm, the contractor and authority having jurisdiction (AHJ) disagreed on the application of the Code. I usually don’t answer this many questions at one time, mainly because I don’t like to get between designers, installers and the AHJ. I’m making an exception this time because the foreman is a reader of Electrical Contractor, so I’ll give my personal interpretation on these questions in the order that they were asked.
A circuit breaker protecting conductors is run from a substation switchgear and terminated to a main located in an industrial facility distribution center. Is this installation considered a feeder or service?
The run of conductors are considered a feeder as the definition indicates in Article 100 of the 2008 NEC.
If considered a feeder, can more than six mains be installed in the facility distribution center?
Generally no, but more than six mains can be installed as long as the installation complies with the Exception No. 1 of 225.32 of the NEC.
If a number of control circuits are run to orderly shutdown the operation of various types of equipment, do switches have to be installed to disconnect these conductors?
No, but the installation must meet the provisions of 225.32, Exception No. 2 and Article 685.
Since a grounding electrode is installed at the substation switchgear, does the Code require an electrode to be installed at the distribution center located in the facility?
Yes, the NEC requires a grounding electrode to be installed at the distribution center as outlined in 250.32 (A), 250.32(B) and 250.32(D).
If classified a feeder, can the grounded conductor in this installation be used as a neutral, bonding jumper and equipment-grounding conductor?
No, see 250.32(B) and the accompanying exception.
Is there a section in the Code that installers can use as a guide to list instructions on the proper methods of terminating the neutral and equipment-grounding conductor?
Yes, find these requirements in 408.40.
Can 4,160-volt cables without shields be used for feeder conductors?
No, see 310.6, Exception No. 1.
Are there sections in the Code that specifically cover the requirements for shields and the grounding of shields?
Yes, 310.6, 300.40 and 310.60(C)(1) cover requirements for grounding and bonding shields.
When preparing conductors for splicing, does the Code have a method that electricians could apply in cases where the manufacturer’s specifications have been misplaced?
Yes, see the last sentence of 300.39.
Is there a procedure in the Code that covers the requirements for installing high-voltage conduits and cables?
Yes, use 310.50, Figure B.310.2 and refer to Tables B.310.5 through B.310.10 and be sure to consult with the AHJ on correct application of the figure and its companion tables.
The electrician foreman had a number of questions on the installation and use of metal cable trays and the associated wiring methods installed. Questions are as follows.
Will the Code allow an elevation or directional change in a metal cable tray run without the use of a manufactured fitting?
Yes, such a change without installing a fitting manufactured by a cable tray company is permitted as long as the requirements of 392.6 and 392.7 are complied with.
Can a number of control circuits be routed with the power circuits where all the circuits are electrically associated? In other words, if one motor or compressor is lost, the entire equipment process fails to operate.
Yes, refer to the requirements outlined in 725.48(B)(4) and 392.8.
When installing many current-carrying conductors in cable tray runs, to obtain the allowable ampacity of each conductor, can electricians select the ampacity of each conductor per Table 310.16 and based on the installation, derate each conductor’s ampacity by the percentages in Table 310.15 (B)(2)(a)?
No, when installing cables and conductors in cable trays, Table 310.15(B)(2)(a) is not always used, electricians must apply the requirements per 392.11 based on single conductors, multiconductors or a combination of both types.
Are there any recommended standards that electricians can use as a guide when installing cable tray systems?
Yes, I have always found that NEMA-VE 1, Metal Cable Trays Systems, and NEMA-VE 2, Metal Cable Tray Installation Guidelines, were very helpful for electricians installing cable tray systems.
STALLCUP is the CEO of Grayboy Inc., which develops and authors publications for the electrical industry and specializes in classroom training on the National Electrical Code and other standards, including those from OSHA. Contact him at 817.581.2206.