With this issue of Electrical Contractor, we're pleased to introduce a new monthly column. "Code Question of the Month" is based on Code Question of the Day (CQD), a free daily online feature presented jointly by Electrical Contractor magazine and the National Electrical Contractors Association's Codes and Standards Committee. Each weekday morning, Code users receive a practical mini-lesson in how to apply the requirements of the 1999 National Electrical Code on the job, delivered automatically to their e-mail addresses.
In the two years that we have operated CQD, our free subscription list has grown to more than 4,000 contractors. That's not bad, but Electrical Contractor magazine reaches nearly 90,000 readers with every issue. That's why we have decided to make the practical, job-related expertise of Code Question of the Day available to a broader audience.
Each month, CQD author Charles M. Trout will expand on a selection of his past daily online questions dealing with a particular subject or problem, using more solid Code-based technical information and his own strong opinions based on decades of practical electrical construction and Code experience. We hope you enjoy this new monthly feature. (To subscribe to our daily online Code Question of the Day, see the box at the end of this article.)
About our author: Charles M. Trout has been an electrical contractor for many years, and is currently associated with Maron Electric Co. in Skokie, Ill. He is chairman of National Electrical Code-making Panel No. 12, a member of the NECA Codes and Standards Committee, and a member of the Western Section of the International Association of Electrical Inspectors.
Brooke Stauffer, director of Codes and Standards
National Electrical Contractors Association
This month's Code question deals with querries submitted by Code Question of the Day subscribers concerning the installation of nonmetallic-sheathed cable. Properly installing nonmetallic cable is not easy. It takes a concerted effort by the installer, who must have knowledge of the requirements of the 1999 National Electrical Code. Following the basic Code requirements will produce an installation "essentially free from hazard" but will most certainly not result in an installation that is "efficient, convenient, or adequate for good service or future expansion of electrical use."
Question: I am wiring a 2,200-square-foot house. It will have about 36 circuits. How am I supposed to route approximately 30 NM cables into the top of a 40-circuit recessed service panel? The way I do it is by installing a 2-inch PVC connector into the top of the panel and feeding the cables through it. That way I save the other knockouts for the larger cables. Is there another way?
Answer: That must be a remarkable sight-30 cables entering a panel enclosure through a 2-inch knockout! I wonder if we might have a conflict with Section 373-8, which does not permit conductors to fill the wiring space at any cross-section to more than a percentage of the cross-sectional area of the space? In addition, attention must be paid to Section 336-18 that requires securing each cable in place within 12-inches of every cabinet. The requirements are not easy to accomplish but they are quite simple to understand.
Section 373-5(c) requires that each cable be secured to the cabinet. For starters, you could run a few multiwire circuits. That would cut you down to about 15 cables. Duplex connectors would knock off a few more. Then you could use the side and bottom knockouts for cable entries. The important thing to remember is that the Code contains the minimum requirements for safety. (That is not minimum safety, but the minimum required for safety.) Don't fight it.
Our second question this month deals with a similar situation, except this panel is surface-mounted. This seemingly simple change requires us to take a nearly opposite view of the technical problem of securing the cables to the panel.
Question: I have a 40-circuit surface-mounted panel set up in the garage of the house I am wiring. I intend to bring all my NM cables through a 2-inch PVC connector in the top of the panel. There will be about 20 cables entering the panel. Is this installation permitted by the National Electrical Code?
Answer: No, but only because the connector you are using does not meet the length requirements for a nonflexible raceway. There are many things to take into consideration. This type of installation could be performed according to a new exception to Section 373-5(c) in the 1999 National Electrical Code.
The basic rule in Section 373-5(c) that each cable must be secured to the panel has been modified by this exception, which applies only to "cables with entirely nonmetallic sheaths" entering the tops of surface-mounted enclosures. Nonmetallic cables may now enter the top of a surface-mounted enclosure through one or more nonflexible raceways not less than 18 inches, or more than 10 feet in length. The new exception to Section 373-5(c) has several conditions that must be followed. It requires:
(a) Each cable to fastened within 12 inches of the outer end of the raceway;
(b) That the raceway extend directly above the panel and not penetrate a structural ceiling;
(c) That there be a fitting on each end of the nonflexible raceway to protect the cables from abrasion, and these fittings must remain accessible after installation;
(d) The raceway must be sealed or plugged at its outer end using an approved means to prevent access to the enclosure through the raceway;
(e) The cable sheath should be continuous through the raceway, and extend into the enclosure not less than 1/4 inch;
(f) The raceway must be fastened at its outer end and at other points in accordance with the Code article applying to that particular wiring method;
(g) The nonflexible raceway conductor has to be filled in accordance with Table 1, Chapter 9, and Section 310-15(b)(2).
Again, be aware of Section 373-8 and do not fill the wiring space in the panel to more than 40 percent of the cross-sectional area of the wiring space. In a future column, we will answer questions relating to the proper support of NM cables in stud spaces, accessible attics, or roof spaces, and what direct bearing Section 110-12 on "Mechanical Execution of Work" has to do with NM cable installations.
But be careful: If you exceed 24 inches in length, then you are subject to the derating required by Section 310-15(b)(2)(a) and its exception No. 3. However, none of these conditions apply in the case you've described, because your PVC connector does not meet the minimum 18-inch requirements of Section 373-5(c) for a nonflexible raceway. The surface-mounted panelboard installation you have described would not be permitted by the 1999 National Electrical Code.
Code Question of the Day: Free Online Newsletter for Code users
Code Question of the Day is a daily online feature for NEC users, presented jointly by Electrical Contractor magazine and NECA Codes and Standards Committee. (Each question also includes the answer to the previous day's question.)
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