---
id:
aliases:
  - nec-110
tags:
  - authorship/other
  - destiny/uncertain
  - status/incomplete
  - topic/construction/electrical
  - type/media
  - exclude-from-word-count
title: "NEC Article 110: Requirements for Electrical Installations"
---
# NEC Article 110: Requirements for Electrical Installations

## Part I. General

### 110.1 Scope.

This article covers general requirements
for the examination and approval, installation and use,
access to and spaces about electrical conductors and equipment;
enclosures intended for personnel entry;
and tunnel installations.

> [!info] Informational Note:
> See Informative Annex J for information regarding ADA accessibility design.

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### 110.8 Wiring Methods

Only wiring methods recognized as suitable
are included in this Code.
The recognized methods of wiring
shall be permitted to be installed
in any type of building or occupancy,
except as otherwise provided in this Code.

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### 110.14 Electrical Connections.

Because of different characteristics of dissimilar metals,
devices such as pressure terminal
or pressure splicing connectors and soldering lugs
shall be identified for the material of the conductor
and shall be properly installed and used.
Conductors of dissimilar metals
shall not be intermixed in a terminal or splicing connector
where physical contact occurs between dissimilar conductors
(such as copper and aluminum or aluminum and copper-clad aluminum),
unless the device is identified for the purpose and conditions of use.
Materials such as solder, fluxes, inhibitors, and compounds,
where employed, shall be suitable for the use
and shall be of a type that will not adversely affect
the conductors, installation, or equipment.
Connectors and terminals for conductors more finely stranded
than Class B and Class C stranding as shown in Chapter 9, Table 10,
shall be identified for the specific conductor class or classes.

#### 110.14(C) Temperature Limitations.

The temperature rating associated with the ampacity of a conductor
shall be selected and coordinated so as not to exceed the lowest
temperature rating of any connected termination, conductor, or device.
Conductors with temperature ratings higher than specified for
terminations shall be permitted to be used
for ampacity adjustment, correction, or both.

##### 110.14(C)(1) Equipment Provisions.

The determination of termination provisions of equipment
shall be based on 110.14(C)(1)(a) or (C)(1)(b).
Unless the equipment is listed and marked otherwise,
conductor ampacities used in determining equipment termination provisions
shall be based on Table 310.16 as appropriately modified by 310.12.

* (a) Termination provisions of equipment for circuits rated 100 amperes or less,
    or marked for 14 AWG through 1 AWG conductors,
    shall be used only for one of the following:
    * (1) Conductors rated 60°C (140°F).
    * (2) Conductors with higher temperature ratings,
      provided the ampacity of such conductors
      is determined based on the 60°C (140°F) ampacity of the conductor size used.
    * (3) Conductors with higher temperature ratings
      if the equipment is listed and identified for use with such conductors.
    * (4) For motors marked with design letters B, C, or D,
      conductors having an insulation rating of 75°C (167°F) or higher
      shall be permitted to be used,
      provided the ampacity of such conductors
      does not exceed the 75°C (167°F) ampacity.

* (b) Termination provisions of equipment
  for circuits rated over 100 amperes,
  or marked for conductors larger than 1 AWG,
  shall be used only for one of the following:
    * (1) Conductors rated 75°C (167°F)
    * (2) Conductors with higher temperature ratings,
      provided the ampacity of such conductors
      does not exceed the 75°C (167°F) ampacity of the conductor size used,
      or up to their ampacity if the equipment is listed and identified
      for use with such conductors

##### 110.14(C)(2) Separate Connector Provisions.

Separately installed pressure connectors shall be used with conductors at the ampacities not exceeding the ampacity at the listed and identified temperature rating of the connector.

Informational Note:
With respect to 110.14(C)(1) and (C)(2),
equipment markings or listing information may additionally restrict
the sizing and temperature ratings of connected conductors.

#### 110.14(D) Terminal Connection Torque.

Tightening torque values for terminal connections
shall be as indicated on equipment
or in installation instructions provided by the manufacturer.
An approved means shall be used to achieve the indicated torque value.

Informational Note No. 1:
Examples of approved means of achieving the indicated torque values
include torque tools or devices such as shear bolts
or breakaway-style devices with visual indicators
that demonstrate that the proper torque has been applied.

Informational Note No. 2:
The equipment manufacturer can be contacted
if numeric torque values are not indicated on the equipment
or if the installation instructions are not available.
Informative Annex I of UL Standard 486A-486B, Standard for Safety-Wire Connectors,
provides torque values in the absence of manufacturer's recommendations.

Informational Note No. 3:
Additional information for torquing threaded connections and terminations
can be found in Section 8.11 of NFPA 70B-2019, Recommended Practice for Electrical Equipment Maintenance.

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## Part II. 1000 Volts, Nominal, or Less

### 110.26 Spaces About Electrical Equipment.

Access and working space shall be provided and maintained about all electrical equipment
to permit ready and safe operation and maintenance of such equipment.

#### 110.26(A) Working Space.

Working space for equipment operating at 1000 volts, nominal, or less to ground
and likely to require examination, adjustment, servicing, or maintenance while energized
shall comply with the dimensions of 110.26(A)(1), (A)(2), (A)(3), and (A)(4)
or as required or permitted elsewhere in this Code.

Informational Note:
NFPA 70E-2018, Standard for Electrical Safety in the Workplace,
provides guidance, such as determining severity of potential exposure,
planning safe work practices including establishing an electrically safe work condition,
arc flash labeling, and selecting personal protective equipment.

### 110.26(A)(1) Depth of Working Space.

The depth of the working space in the direction of live parts
shall not be less than that specified in Table 110.26(A)(1) unless the
requirements of 110.26(A)(1)(a), (A)(1)(b), or (A)(1)(c) are met.
Distances shall be measured from the exposed live parts
or from the enclosure or opening if the live parts are enclosed.

### Table 110.26(A)(1) Working Spaces

Minimum Clear Distance

| Nominal Voltage to Ground | Condition 1   | Condition 2        | Condition 3   |
| ------------------------- | ------------- | ------------------ | ------------- |
| 0–150                     | 900 mm (3 ft) | 900 mm (3 ft)      | 900 mm (3 ft) |
| 151–600                   | 900 mm (3 ft) | 1.0 m (3 ft 6 in.) | 1.2 m (4 ft)  |
| 601–1000                  | 900 mm (3 ft) | 1.2 m (4 ft)       | 1.5 m (5 ft)  |

Note: Where the conditions are as follows:

* Condition 1 -- Exposed live parts on one side of the working space
  and no live or grounded parts on the other side of the working space,
  or exposed live parts on both sides of the working space
  that are effectively guarded by insulating materials.

* Condition 2 -- Exposed live parts on one side of the working space
  and grounded parts on the other side of the working space.
  Concrete, brick, or tile walls shall be considered as grounded.

* Condition 3 -- Exposed live parts on both sides of the working space.

(a) _Dead-Front Assemblies._
Working space shall not be required in the back or sides of assemblies, such as dead-front switchboards, switchgear, or motor control centers, where all connections and all renewable or adjustable parts, such as fuses or switches, are accessible from locations other than the back or sides. Where rear access is required to work on nonelectrical parts on the back of enclosed equipment, a minimum horizontal working space of 762 mm (30 in.) shall be provided.

(b) _Low Voltage._
By special permission, smaller working spaces shall be permitted where all exposed live parts operate at not greater than 30 volts rms, 42 volts peak, or 60 volts dc.

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#### 110.26(C)(3) Personnel Doors.

Where equipment rated 800 amperes or more that contains overcurrent devices,
switching devices, or control devices is installed
and there is a personnel door(s) intended for entrance to and egress from the working space
less than 7.6 m (25 ft) from the nearest edge of the working space,
the door(s) shall open in the direction of egress
and be equipped with listed panic hardware or listed fire exit hardware.

Informational Note:
For information on panic hardware, see UL 305, Standard For Safety For Panic Hardware.
For fire exit hardware, see UL 305, Standard For Panic Hardware,
and UL 10C, Standard for Safety for Positive Pressure Fire Tests of Door Assemblies.

#### 110.26(D) Illumination.

Illumination shall be provided for all working spaces about service equipment,
switchboards, switchgear, panelboards, or motor control centers installed indoors.
Control by automatic means shall not be permitted
to control all illumination within the working space.
Additional lighting outlets shall not be required
where the work space is illuminated by an adjacent light source
or as permitted by 210.70(A)(1), Exception No. 1, for switched receptacles.

#### 110.26(E) Dedicated Equipment Space.

All switchboards, switchgear, panelboards, and motor control centers
shall be located in dedicated spaces and protected from damage.

> [!important] Exception
> Control equipment that by its very nature
> or because of other rules of the Code
> must be adjacent to or within sight of its operating machinery
> shall be permitted in those locations.

#### 110.26(E)(1) Indoor.

Indoor installations shall comply with 110.26(E)(1)(a) through (E)(1)(d).

* (a) _Dedicated Electrical Space._
  The space equal to the width and depth of the equipment
  and extending from the floor to a height of 1.8 m (6 ft) above the equipment
  or to the structural ceiling, whichever is lower,
  shall be dedicated to the electrical installation.
  No piping, ducts, leak protection apparatus,
  or other equipment foreign to the electrical installation
  shall be located in this zone.

  > [!important] Exception
  > Suspended ceilings with removable panels shall be permitted within the 1.8 m (6-ft) zone.

* (b) _Foreign Systems._
  The area above the dedicated space required by 110.26(E)(1)(a)
  shall be permitted to contain foreign systems,
  provided protection is installed to avoid damage to the electrical equipment
  from condensation, leaks, or breaks in such foreign systems.

* (c) _Sprinkler Protection._
  Sprinkler protection shall be permitted for the dedicated space where the piping complies with this section.

* (d) _Suspended Ceilings._
  A dropped, suspended, or similar ceiling that does not add strength to the building structure shall not be considered a structural ceiling.

#### 110.26(E)(2) Outdoor.

Outdoor installations shall comply with 110.26(E)(2)(a) through (E)(2)(c).

* (a) Installation Requirements. Outdoor electrical equipment shall be the following:

  1. Installed in identified enclosures
  2. Protected from accidental contact by unauthorized personnel or by vehicular traffic
  3. Protected from accidental spillage or leakage from piping systems

* (b) Work Space. The working clearance space shall include the zone described in 110.26(A). No architectural appurtenance or other equipment shall be located in this zone.

* (c) Dedicated Equipment Space. The space equal to the width and depth of the equipment, and extending from grade to a height of 1.8 m (6 ft) above the equipment, shall be dedicated to the electrical installation. No piping or other equipment foreign to the electrical installation shall be located in this zone.

  Exception: Structural overhangs or roof extensions shall be permitted in this zone.

#### 110.26(F) Locked Electrical Equipment Rooms or Enclosures.

Electrical equipment rooms or enclosures housing electrical apparatus that are controlled by a lock(s) shall be considered accessible to qualified persons.
