National Electrical Code Article 110 Requirements for Electrical Installations

Guarding live parts against accidental contact. (50-1000 volts)

(1) Locating equipment in a room, vault, or similar enclosure that is accessible only to qualified persons. (2) By permanent, substantial partitions or screens arranged so that only qualified persons have access to the space within reach of the live parts. Any openings in such partitions or screens shall be sized and located so that persons are not likely to cone into accidental contact with the live parts or to bring conducting objects into contact with them. (3)by location on balcony, gallery, or platform elevation and arranged so as to exclude qualified persons. (4)By elevation above the floor or other working surface.

Outdoor installation requirements

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

Working Space Requirements for condition 3

0-150 volts- 3ft, 151-600 volts-4 ft, 601-1000 volts 5 ft

Working space requirements for condition 2

0-150 volts-900mm (3ft), 151-600 volts- 1 meter (3.5 ft), 600-1000 volts-1.2 meters (4 ft)

Working space requirements for Condition 1

900mm (3ft) for 0-1000 voltage to ground

Conductor Size is measured in

American Wire Gauge (AWG) or circular mils.

Entrance to and egress from working spaces minimum requirements

At least one entrance of sufficient area shall be provided to give access to and egress from working space about electrical equipment.

Electrical Connections.

Because of the 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 shall be properly installed and used.

Wiring Integrity means

Complete wiring installations shall be free of short circuits, ground faults, or any connections to ground other than as required or permitted elsewhere in this code.

Splices

Conductors shall be spliced or joined with splicing devices identified for the use or by brazing, welding, or soldering with a fusible metal or alloy. Soldering splices shall first be spliced or joined so as to be mechanically and electrically secure without solder and then be soldered.

Mounting Electrical Enclosures

Electrical equipment shall be firmly secured to the surface on which it is mounted. wooden plugs driven into holes in masonry, concrete, plaster, or similar materials shall not be used.

Arc-Flash Hazard Warning

Electrical equipment, such as switchboards, switchgear, panel boards, industrial control panels, meter socket enclosures, and motor control centers, that is in other than dwelling units, and is likely to require examination, adjustment, servicing, or maintenance while energized, shall be field or factory marked to warn qualified persons of potential electric arc flash hazards. the marking shall meet the requirements in 110.21 (b) and shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.

Interrupting Rating

Equipment intended to interrupt current at fault levels shall have an interrupting rating at nominal circuit voltage with at least equal to the current that is available at the line terminals of the equipment.

Working space condition 1 definition

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 are effectively guarded by insulating materials.

Unused current transformers

If associated with potentially energized circuits shall be short circuited.

OSHA

Occupational Safety and Health Administration

Unused openings in electrical equipment

Shall be closed to afford protection substantially equivalent to the wall of the equipment. Where metallic plugs or plates are used with nonmetallic enclosures that shall be recessed at least 6mm (1/4 in) from the outer surface of the enclosure

Vault doors are required to be equipped with locks

True

Modifications to electrical installations.

When modifications to the electrical installation occur that affect the maximum available fault current at the service, the maximum available fault current shall be verified or recalculated as necessary to ensure the service equipment ratings are sufficient for the maximum available fault current at the line terminals of the equipment.

Electrical vault doors

each doorway leading into a vault from the building interior shall be provided with a tight fitting door that has a minimum fire rating of 3 hours. The authority having jurisdiction shall be permitted to require such a door for an exterior wall opening where conditions warrant.

Tunnel installations over 1000v Grounded and Bonded

All non current carrying metal parts of electrical equipment and all metal raceways and cable sheaths shall be solidly grounded and bonded to all metal pips and rails at the portal and at intervals not exceeding 300m (1000 ft) throughout the tunnel.

Dedicated equipment space requirements

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

Terminal requirements

Connection of conductors to terminal parts shall ensure a thoroughly good connection without damaging the conductors and shall be made by means of pressure connectors (including set screw type), solder lugs, or splices to flexible leads. Connection by means of wire-binding screws or studs and nuts sthat have unturned lugs or equivalent shall be permitted for 10 AWG or smaller conductors.

Identification of Disconnecting Means

Each disconnecting means shall be legibly marked to indicate its purpose unless located and arranged so the purpose is evident. The Marking shall be of sufficient durability to withstand the environment involved.

Tunnel Ventilation system controls

Electrical controls for ventilation systems shall be arranged so that the airflow can be reversed.

Electrical equipment cooling.

Electrical equipment provided with ventilation openings shall be installed so that walls or other obstructions do not prevent the free circulation of air through the equipment. For equipment designated for floor mounting, clearance between top of surfaces and adjacent surfaces shall be provided to dissipate rising warm air.

Working space condition 2 definition

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

Working space Illumination

Illumination shall be provided for all working spaces about service equipment, switchboards, switchgear, panel boards, or motor control centers installed indoors, control by automatic means only shall not be permitted. Additional lighting outlets shall not be required where the work space is illuminated by adjacent light source.

Equipment Markings, Equipment ratings

Markings indicating voltage, current, wattage or other ratings shall be provided as specified. The marking or label shall be sufficient durability to withstand the environment involved.

Conductors

Normally used to carry current. Shall be of copper or aluminum unless otherwise provided in this code. Where the conductor material is not specified, the sizes given in this code shall apply to copper conductors. Where other materials are used, the size shall be changed accordingly.

High-Leg Marking

On a 4 white, delta connected system where the midpoint of one phase winding is grounded, only the conductor or busbar having the higher phase voltage to ground shall be durably and permanently marked by an outer finish that is orange in color or by other effective means. Such identification shall be placed at each point on the system where connection is made if the grounded conductor is also present.

Listing

Product testing, evaluation and listing (product certification) shall be performed by recognized qualified electrical testing laboratories and hall be in accordance with applicable product standards recognized as achieving equivalent and effective safety for equipment installed to comply with this code.

Reconditioned equipment markings

Reconditioned equipment shall be marked with the name, trademark, or other descriptive marking by which the organization responsible for the reconditioning of the electrical equipment can be identified, along with the date of the reconditioning.

Available Fault Current, Field Marking

Service equipment at other than dwelling units shall be legibly marked in the field with the maximum available fault current. the field marking shall include the date the fault-current calculation was performed and be of sufficient durability to withstand the environment involved. The calculation shall be documented and made available to those authorized to design, install, inspect, maintain or operate the system.

Electrical vaults floors.

The floors of vaults in contact with the earth shall be of concrete that is not less than 102mm (4in) thick, but where the vault is constructed with a vacant space or other stories below it, the floor shall have adequate structural strength for the load imposed on it and a minimal fire resistance of 3 hours.

Equipment Markings, manufacture identification requirements.

The manufacturer's name, trademark or other descriptive marking by which the organization responsible for the product can be identified shall be placed on all electrical equipment.

Field-Applied hazard Marking

The marking shall warn of the hazards using effective words, colors, symbols, or any combination thereof. Label shall be permanent affixed to the equipment or wiring method and shall not be handwritten and the label shall be able to withstand the environment involved.

Voltage ratings for equipment

The voltage rating of electrical equipment shall not be less than the nominal voltage of a circuit to which it is connected.

Electrical vault walls and roofs

The walls and roof shall be constructed of materials that have adequate structural strength for the conditions, with a minimum fire rating of 3 hours. for the purpose of this section, studs and wallboard construction shall not be permitted.

Width of working space (in front of equipment, requirements)

The width of the working space in front of the electrical equipment shall be the width of the equipment or 762mm (30 in), whichever is greater. In all cases, the work space shall permit at least a 90 degree opening of equipment doors or hinged panels.

Height of working space requirements

The work space shall be clear and extend from the grade, floor, or platform to a height of 2.0 meters (6 1/2 ft) or the height of the equipment, whichever is greater. Within the height requirements of this section, other equipment that is associated with the electrical installation and is located above or below the electrical equipment shall be permitted to extend not more than 150mm (6in) beyond the front of the electrical equipment.

Personal door requirements

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

Separation from High Voltage equipment

Where switches, cutouts, or other equipment operating at 1000 volts, nominal, or less are installed in a vault, room, or enclosures where there are exposed live parts or exposed wiring operating over 1000 volts, nominal, the high voltage equipment shall be effectively separated from the space occupied by the low-voltage equipment by suitable partition, fence, or screen.

Working space condition 3 definitions

exposed live parts on both sides of the working space (a) where equipment is installed above a lay-in ceiling there shall be an opening not smaller than 22in x 22in, or in a crawl space there shall be an accessible opening not smaller than 22in x 30in, whichever is greater. (b) the width of the working space shall be the width of the equipment enclosure or a minimum of 30in, whichever is greater. (c) All enclosure doors or hinged panels shall be capable of opening a minimum of 90 degrees. (d) The space in front of the enclosure shall comply with a depth requirement of table 110.26(a)(1). The maximum height of the working space shall be the height necessary to install the equipment in the limited space. A horizontal ceiling structural member or access panel shall be permitted in this space

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, copper 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 and shall be of a type that will not adversely affect the conductors, installation or equipment.