NEC Code Tips

Article 110 – General Requirements Part 1 of 2

February, 2000

Approval of Equipment [110-2]

The authority having jurisdiction, which is generally the electrical inspector, must approve all electrical equipment prior to installation. The principal basis for the approval of equipment by the inspector is listing and/or labeling by Nationally Recognized Testing Laboratories (NRTL) [90-7].

Note: Listing or labeling does not mean the inspector will automatically permit the equipments use.

Examination, Identification, Installation, and Use of Equipment [110-3(b)]

Electrical equipment must be installed, and/or used according to its listed and labeled instructions and the failure to follow manufacture instructions, such as torque requirements, conductor sizing, etc, is a violation of this Code rule.

Because equipment is listed with specific conditions of use, operation, or installation, it is important that equipment be installed according to the instructions. Example: Air-conditioning equipment nameplates often include the following “Maximum Fuse Size”. This means that the equipment must have overcurrent protect by the use of fuses, and circuit breakers are not suitable.

Voltages [110-4]

Equipment must be installed on a nominal voltage system that does not exceed the voltage rating of the equipment and in addition, electrical equipment must not be connected to a nominal voltage source that is less than the equipment rated [110-3(b)].

Copper Conductors [110-5]

When the Code refers to a conductor size, it's in reference to the material of copper (CU), unless aluminum is specifically specified in the rule.

Conductor Sizes [110-6]

Conductor sizes in the Code are expressed in American Wire Gauge (AWG) or circular mils, except for conductor larger than No. 4/0 AWG, which are identified in kcmils (thousand circular mils). Example: 250 kcmils or 250,000 circular mils.

Conductor Insulation [110-7]

All electrical wiring must be installed so that when its completed, it will be free from short-circuits, and improper grounds. The most common violation of this rule is the intentional or accidental bonding of the neutral conductor to the equipment grounding conductor in violation of Section 250-142.

Note: When a conductor is no longer used (has been abandoned), the end of the conductor must be covered with an insulation equivalent to that of the conductors or with an insulating device identified for the purpose, such as a twist-on wire connector [110-14(b)].

Wiring Methods [110-8]

Only the wiring methods listed in Articles 318 through 384 are considered suitable for the installation of electrical systems. This would include but (not limited to): armored cable, nonmetallic sheath cable, EMT, rigid and/or flexible metal and/or nonmetallic conduit. An example of a common Code violation is the use of sprinkler piping and fitting for electrical wiring.

Interrupt Protection Rating [110-9]

Overcurrent protection devices, such as circuit breakers and fuses, are intended to open the circuit at very high fault current levels. Therefore overcurrent protection devices must have an interrupting ampere rating sufficient for the maximum possible fault-current available on the line terminals of the overcurrent protection device. If the overcurrent protection device is not rated for the available fault-current, it could explode while attempting to clear the fault, and/or the downstream equipment could suffer serious damage, causing possible hazards to people.

DANGER: If the available fault-current exceeds the controller’s short-circuit current rating, the controller could literally explode endangering persons and property. To solve this problem, a current-limiting protection device (fast-clearing fuse) can be used to reduce the let-thru energy to less than 5,000 ampere.

Note: For more information and spreadsheet calculators on this subject, go to

The above tips were extracted from the book Understanding the 1999 National Electrical Code written by Mike Holt. This book can be ordered over the Internet or by calling Mike Holt Enterprises, Inc., 1-888 NEC CODE (632-2633).

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