requirements for electrical installations

2Requirements for Electrical Installations

2.1.1 Description of Fuse Class Designations2.1.2 Maximum Peak Let-Through Current (Ip-Amperes) and Clearing I2t(Amperes-Squared-Seconds)2.2.1 Working Spaces [NEC Table 110.26(A)]2.2.2 Examples of Conditions 1, 2, and 3 (Working Spaces)2.2.3 Example of Exception 1 (Working Spaces)2.2.4 Example of Exception 3 (Working Spaces)2.2.5 Required 30-In-Wide Front Working Space (Working Spaces)2.2.6 Required Full 90-Degree Opening of Equipment Doors (Working Spaces)2.3.1 NEC Section 110.26(C), Basic Rule, First Paragraph (Access to Working

Space)2.3.2 NEC Section 110.26(C), Basic Rule, Second Paragraph (Access to Working

Space)2.3.3 Example of an Unacceptable Arrangement of a Large Switchboard (Access

to Working Space)2.3.4 Example of Exception No. 1 (Access to Working Space)2.3.5 Example of Exception No. 2 (Access to Working Space)2.4.1 Working Space and Dedicated Electrical Space2.4.2 Working Space in Front of a Panelboard as Required by NEC Section 110.262.4.3 Dedicated Electrical Space Over and Under a Panelboard2.5.1 Minimum Depth of Clear Working Space at Electrical Equipment2.5.2 Elevation of Unguarded Live Parts Above Working Space

Section

2.1

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2.1.1 Description of Fuse Class Designations

2.2 Section Two

TABLE 2.1.1

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Requirements for Electrical Installations 2.3

2.1.2 Maximum Peak Let-Through Current(Ip-Amperes) and Clearing I 2t(Amperes-Squared-Seconds)

TABLE 2.1.2

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2.2.1 Working Spaces

2.4 Section Two

Exception No. 1. Working space shall not be required in back or sides ofassemblies, such as dead-front switchboards or motor control centers, wherethere are no renewable or adjustable parts, such as fuses or switches, on theback or sides and where all connections are accessible from locations otherthan the back or sides. Where rear access is required to work on deenergizedparts on the back of enclosed equipment, a minimum working space of 30 in(762 mm) horizontally shall be provided.

Exception No. 2. By special permission, smaller spaces shall be permittedwhere all uninsulated parts are at a voltage no greater than 30 V rms, 42 Vpeak, or 60 V dc.

Exception No. 3. In existing buildings where electrical equipment is beingreplaced, condition 2 working clearance shall be permitted between dead-front switchboards, panelboards, or motor control centers located across theaisle from each other where conditions of maintenance and supervisionensure that written procedures have been adopted to prohibit equipment onboth sides of the aisle from being open at the same time and qualified per-sons who are authorized will service the installation.

TABLE 2.2.1

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2.2.2 Examples of Conditions 1, 2, and 3 (Working Spaces) Distances are measured from thelive parts if the live parts are exposed, or from the enclosure front if live parts are enclosed. If any assemblies, such as switchboardsor motor-control centers, are accessible from the back and expose live parts, the working clearance dimensions would be required atthe rear of the equipment, as illustrated. Note that for Condition 3, where there is an enclosure on opposite sides of the workingspace, the clearance for only one working space is required.


2.2.2

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2.2.3 Example of Exception 1 (Working Spaces)

2.6 Section Two

2.2.4 Example of Exception 3 (Working Spaces)

2.2.3

2.2.4

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2.2.5 Required 30-In-Wide Front Working Space (Working Spaces) The 30-inch-wide frontworking space is not required to be directly centered on the electrical equipment if it can be ensured that the space is sufficient forsafe operation and maintenance of such equipment.


2.2.5

2.2.6 Required Full 90-Degree Opening of Equipment Doors (Working Spaces)Equipment doors are required to open a full 90 degrees to ensure a safe working space.

2.2.6

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2.3.1 NEC Section 110.26(C), Basic Rule, First Paragraph (Access to WorkingSpace) Section 110.25 (C), Basic Rule, first paragraph. At least one entrance is required to provide access to the workingspace around electrical equipment. The installation shown on the bottom would not be acceptable if the electrical equipment was aswitchboard over 6 feet wide and rated 1200 amperes or more.

2.8 Section Two

2.3.1

2.3.2 NEC Section 110.26(C), Basic Rule, Second Paragraph (Access to WorkingSpace) Section 110.26 (C), Basic Rule, second paragraph. For equipment rated 1200 amperes or more and over 6 feet wide, one entrance not less than 24 inches wide and 6-1/2 feet high is required at each end.

2.3.2

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2.3.3 Example of an Unacceptable Arrangement of a Large Switchboard (Access toWorking Space) Unacceptable arrangement of large switchboard—a person could be trapped behind arcing electrical

equipment.


2.3.3

2.3.4 Example of Exception No. 1 (Access to Working Space) The equipment location

permits a continuous and unobstructed way of exit travel.

2.3.4

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2.3.5 Example of Exception No. 2 (Access to Working Space) If the working space requiredby Section 110.26 (A) is doubled, only one entrance to the working space is required.

2.10 Section Two

2.3.5

2.4.1 Working Space and Dedicated Electrical Space The two distinct indoor installation spacesrequired by Section 110.26 (A) and 110.26 (F), that is, the “working space” and the “dedicated electrical space.”

2.4.1

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2.4.2 Working Space in Front of a Panelboard as Required by NEC Section 110.26The working space in front of a panelboard as required by Section 110.26. This illustration supplements the dedicated equipmentspace shown in Figure 2.4.3.


2.4.2

2.4.3

2.4.3 Dedicated Electrical Space Over and Under a Panelboard The dedicated electrical

space over and under a panelboard, as required by Section 110.26 (F) (1).

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2.5.1 Minimum Depth of Clear Working Space at Electrical Equipment [NEC Table 110.34(A)]

2.12 Section Two

TABLE 2.5.1

2.5.2 Elevation of Unguarded Live Parts Above Working Space [NEC Table 110.34(A)]

TABLE 2.5.2

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requirements for electrical installations

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