Article 300: General Requirements for Wiring Methods and Materials

Part I. General Requirements

300.1 Scope.

300.1(A) All Wiring Installations.

This article covers general requirements for wiring methods and materials for all wiring installations unless modified by other articles in Chapter 3.

300.1(B) Integral Parts of Equipment.

The provisions of this article are not intended to apply to the conductors that form an integral part of equipment, such as motors, controllers, motor control centers, or factory-assembled control equipment or listed utilization equipment.

300.1(C) Metric Designators and Trade Sizes.

Metric designators and trade sizes for conduit, tubing, and associated fittings and accessories shall be as designated in Table 300.1(C).

Table 300.1(C) Metric Designators and Trade Sizes

Metric Designator	Trade Size
12	3/8
16	1/2
21	3/4
27	1
35	1-1/4
41	1-1/2
53	2
63	2-1/2
78	3
91	3-1/2
103	4
129	5
155	6

300.19 Supporting Conductors in Vertical Raceways.

300.19(A) Spacing Intervals -- Maximum.

Conductors in vertical raceways shall be supported if the vertical rise exceeds the values in Table 300.19(A). At least one support method shall be provided for each conductor at the top of the vertical raceway or as close to the top as practical. Intermediate supports shall be provided as necessary to limit supported conductor lengths to not greater than those values specified in Table 300.19(A).

Table 300.19(A) Spacings for Conductor Supports

Conductor Size	Aluminum or Copper-Clad Aluminum	Copper
18 AWG through 8 AWG	100ft	100ft
6 AWG through 1/0 AWG	200ft	100ft
2/0 AWG through 4/0 AWG	180ft	80ft
Over 4/0 AWG through 350 kcmil	135ft	60ft
Over 350 kcmil through 500 kcmil	120ft	50ft
Over 500 kcmil through 750 kcmil	95ft	40ft
Over 750 kcmil	85ft	35ft

300.19(B) Fire-Rated Cables and Conductors.

Support methods and spacing intervals for fire-rated cables and conductors shall comply with any restrictions provided in the listing of the electrical circuit protective system used and in no case shall exceed the values in Table 300.19(A).

300.19(C) Support Methods.

One of the following methods of support shall be used:

Clamping devices constructed of or employing insulating wedges inserted in the ends of the raceways. Where clamping of insulation does not adequately support the cable, the conductor also shall be clamped.
Inserting boxes at the required intervals in which insulating supports are installed and secured in an approved manner to withstand the weight of the conductors attached thereto, the boxes being provided with covers.
In junction boxes, deflecting the cables not less than 90 degrees and carrying them horizontally to a distance not less than twice the diameter of the cable, the cables being carried on two or more insulating supports and additionally secured thereto by tie wires, if desired. Where this method is used, cables shall be supported at intervals not greater than 20 percent of the support spacing in Table 300.19(A).
Other approved means.

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