Section 3: Requirements for Electrical Installations

3.1 Examination, Identification, Installation, and Use of Equipment
3.2 Installation and Use
3.3 Interrupting Rating
3.4 Electrical Connections – Temperature Limitations
3.5 Arc Flash Hazard Warning
3.6 Arcing Parts
3.7 Identification of Disconnecting Means
3.8 Available Fault Current
3.9 Depth, Width and Height of Working Space
3.10 Large Equipment
3.11 Height of Working Space and Illumination
3.12 Dedicated Equipment Space
3.13 Enclosure Selection
3.14 Over 600 Volts. Entrance and Access to Work Space
3.15 Over 600 Volts, Working Space

3.1 Examination, Identification, Installation, and Use of Equipment
Equipment is required to be marked indicating its suitability for use.

Equipment is designed for a specific purpose and it must be installed for that purpose.  Panelboards are designed to house circuit breakers and are not designed to be used as junction boxes, unless adequate space is provided.  Indoor enclosures are designed for dry locations and cannot be used outdoors, exposed to the weather.  Disconnects used as service equipment must be suitable for use as service equipment.  Luminaries used inside a paint booth where combustible liquid is sprayed must be designed and listed for a Class 1 Division 1 Classified location.

Equipment must be installed to meet the purpose and intended design of the manufacturer.  Equipment is classified by type, size, voltage, current capacity and specific use.  The suitability of a piece of equipment for a particular application is shown by listing or labeling of the equipment by a third party testing agency, like Underwriters Laboratories.

When a testing agency examines equipment they look for qualities such as strength and durability, wire-bending and connection space, electrical insulation, and heating effects under normal and abnormal conditions.  They also check enclosures for electrical equipment to be sure there are not exposed parts that can be touched or reached by someone using the equipment.


Review Question Section 3.1

15. When a third party testing agency examines electrical equipment, which of the following is not included in the examination?


3.2 Installation and Use

Installing equipment according to the NECî means installing it in accordance with the manufacturer’s listing and labeling.  When manufacturers submit their equipment for evaluation and listing, the equipment is submitted with specific requirements for installation.  These installation instructions them become part of the listing; and the NECî requires the equipment to be installed per the instructions.

Inspection departments require listing and labeling because inspectors do not have the standards, tools, time, or expertise to examine equipment in the detail required to make a thorough evaluation.  Listing and labeling is therefore necessary to assure equipment is safe for its intended use.

Sometimes, the manufacturer’s instructions for listed equipment exceed the minimum requirements of the NECî.  For example, if the nameplate of an HVAC unit specifies a minimum circuit ampacity of 40-amps and calls for a minimum circuit conductor size of No. 6 AWG copper, then a No. 6 copper conductor is required to meet Code.  Because No. 6 copper is part of the listing it is the smallest conductor that is permitted to be used.


Review Question Section 3.2

16. Which of the following statements about equipment installation instructions is true?

Equipment shall be installed and used in accordance with its listing & labeling.

3.3 Interrupting Rating
The interrupting rating of a device cannot be less than the available fault current.

Circuit breakers are rated according to their trip setting. They are also classified according to their interrupting rating at the voltage available at the line terminals of the equipment.

The interrupting rating of a device is the amount of current it can take without blowing up. Most branch circuit type breakers have an interrupting rating of 10,000-amps. This means the circuit breaker can withstand that much fault current without causing an explosion.

If a 20-amp circuit breaker took a 10,000-amp fault it probably could not be put back in service. But the interrupting rating does not mean the device has to ever work again. It just means the breaker cannot explode and create a hazard to anyone in the area.

Whenever overcurrent devices are exposed to current levels above their interrupting rating the arc flash and arc blast pose a serious threat to electrical workers. It is very important that the interrupting rating of overcurrent devices is not less than the available short circuit current in order to protect equipment and personnel.

If the utility company installs larger capacity transformers, or if a distribution system is expanded and enlarged, it is possible the short circuit current available at the terminals of fuses and circuit breakers is greater than the interrupting rating of those devices. This can be a very dangerous situation and is a clear Code violation.


Review Question Section 3.3

17. The available short circuit current at the terminals of a 100-A circuit breaker is 15,000 -amps. What is the minimum value required for the interrupting rating of the breaker?


3.4 Electrical Connections – Temperature Limitations

In general this section is above the general knowledge needed for inspectors and thermographers.

Circuit breakers and fuseholders have terminals to attach wires to the circuit breaker or fuseholder. The overcurrent device is the beginning of the branch circuit or feeder and there must be a terminal to connect the conductor. In fact, a circuit breaker is an assembly which includes the tripping mechanisms and the means to attach a conductor. A fuseholder is also an assembly which is made to hold a fuse of a certain voltage and current rating and the means to connect a conductor. If the terminal gets overheated it can adversely affect the operation of the fuse or circuit breaker.

To prevent overheating at the terminals, Section 110.14(C) requires the rating of the wire to be equal or greater than the rating of the terminal. The UL marking guide for Molded Case Circuit Breakers explains: All circuit breakers rated 125A or less are marked for use with 60 degree C, 60/75 degree C, or 75 degree C only wire. This marking indicates the proper wire size for termination in accordance with Table 310.15(b)(16) of the NEC. It is acceptable to use wire with a higher insulation rating if the ampacity is based on the wire temperature rating marked on the breaker.

Most terminals today are marked 60/75 degree C or 75 degree C. This means that whatever the ampere rating of the overcurrent device, the 75 degree C rating of the wire, taken from Table 310.15(b)(16), can be used to select the conductor. If the terminal is marked for 60 degree C conductors, the ampacity of the conductor must be selected from the 60 degree column of Table 310.15(B)(16) even if the conductor is rated for 90 degrees.

In general, the 90 degree C ampacity ratings for conductors is only used in de-rating for ambient temperature and when there are more than 3 current carrying conductors in conduit. The 90 degree C ampacity ratings of conductors cannot be used because in wiring for 1000 volts and below there are no overcurrent devices with 90 degree C rated terminals.

Mountain View


Review Question Section 3.4

18. What is the minimum size THHN, 90 degree C conductor for a 100-amp circuit breaker with 75 degree C rated terminals.

The terminal temperature rating of the equipment is used to select the conductor ampacity.

3.5 ARC Flash Hazard Warning
Labels applied to the outside of electrical equipment provide an arc flash hazard warning.

Many commercial and industrial types of equipment require arc flash hazard warning labels, including:

  • Switchboards
  • Switchgear
  • Panelboards
  • Industrial control panels
  • Meter socket enclosures
  • Motor control centers

Arc Flash hazard warnings are not required for equipment installed in dwelling units.  Arc Flash hazard warnings in commercial locations must (1) Use standardized colors and language.  (2) Be permanently attached to the equipment and cannot be handwritten.  (3) The label must be suitable for the environment involved.  NEC Article 110.21 applies to labels.

An arc flash can cause serious damage to equipment and injury to personnel.  The explosion from electrical faults rapidly vaporizes the conductors and metals involved in the fault and melted metal is blown with extreme force in all directions by the explosion.

Individuals injured in arc flash accidents are often severely burned or killed.  Only personnel who have completed training is safe work practices, as outline in NFPA 70E, are qualified to work on equipment marked with an arc flash hazard warning label.  NFPA 70E training covers safe work practices and the selection of various types of Personal Protective Equipment (PPE) required when working on or near energized equipment.


Review Question Section 3.5

19. Which types of electrical equipment do not require an arc flash warning label?


3.6 Arcing Parts

The NEC states that, “Parts of electrical equipment that in ordinary operation produce arcs, sparks, flames, or molten metal shall be enclosed or separated and isolated from all combustible material.”

Fuses and circuit breakers must be installed in enclosures so that under fault conditions if an arc occurs it will not cause injury to anyone in the vicinity.  Luminaries installed over Class 1 Division 11 hazardous (classified) locations are required to be of the totally enclosed type to prevent sparks from reaching flammable material or gases.  Motors that arc while in operation must be enclosed to protect adjacent material from catching fire.  Switches can produce an arc and must be installed in an enclosure to guard the live parts and shield personnel and  other equipment from the danger of arcing parts.


Review Question Section 3.6

20. Parts of electric equipment that in ordinary operation produce arcs shall be enclosed or separated and isolated from all ________ material.

Enclosures contain arcs from electrical equipment and prevent persons from contacting energized parts.

3.7 Identification of Disconnecting Means.
The labels on these disconnects clearly indicate their purpose.

Each disconnecting means shall be legible marked to indicate its purpose unless located and arranged so the purpose is evident.  What is evident is a judgment call.

For example, in some jurisdictions the location is accepted as evidence of purpose when a disconnect is mounted adjacent to a water-heater or mounted on the side of rooftop HVAC equipment.  However, what is evident to an installer may not be evident to an operator.

The requirement for the identification of disconnecting means to be durable does not necessarily require an engraved plastic nameplate.  However, the labeling must be done according to NEC article 110.21 that requires using standardized colors and words or symbols.  The identification label must also be attached to the equipment and cannot be hand written.  The label must be suitable for the environment, so if the equipment is outdoors, the labels must be weatherproof.

Self-adhesive marking labels similar to those used in this illustration are commonly available and comply with Code requirements.

The labels in this illustration comply with the requirements of NEC article 110.22(A) by clearly identifying each load by both function and by horse power.  However, if there was more than one 480-V, 100 HP Compressor or more than one 100 HP Dryer these labels would not be specific enough to clearly identify the loads supplied by the disconnects.


Review Question Section 3.7

21. Each disconnecting means shall be marked to indicate its _________.


3.8 Available Fault Current

NEC Article 110.24 requires the maximum available fault current to be field marked on service equipment, except at dwelling units.  The field marking must be legible and able to withstand the environment where the service equipment is located.  The field marking must include the date when the fault current calculation was performed.

When the service equipment is modified, or when changes are made that might change the maximum available fault current, the fault current calculation must be recalculated and the equipment marked with the new values and the date when the most recent calculation was done.

The maximum available fault current at a service can also be affected by changes made by the utility company. For example, available fault current is usually affected anytime the utility company changes a transformer supplying a facility. However, changes made by a utility remote from a facility such as relocating a substation to change the length of the primary supplying a facility can also affect the available fault current for all of the facilities, supplied by the substation. The only way to ensure that changes made by a utility do not affect a facility is to maintain communication between the facility engineering staff and the utility, and to have engineering calculations done at the facility to determine maximum available fault current when changes are made on either side of the service panel.

An exception allows industrial installations with qualified personnel to skip the field marking requirement.

The available fault current at the terminals of the utility delivery point should be readily available from the utility. Marking it on the equipment with the date will make it easier to confirm the interrupting rating of the equipment is with the range of the available fault current and how long ago the calculation was made.

An Informational Note clarifies that the available fault current is to be used for determining the required short-circuit current ratings of equipment. It is not to be used to establish hazard risk boundaries or the necessary PPE required by qualified persons when working on energized equipment. NFPA 70E, Standard for Electrical Safety in the Workplace, should be used for personnel safety issues when equipment must be serviced while energized.


Review Question Section 3.8

22. Which of the following is an acceptable label to be posted on the service equipment showing the available fault current?

The available fault current must be marked on service equipment at non-dwelling unit locations. (Marking is located at the bottom left of this photo)

3.9 Depth, Width and Height of Working Space
Working space has 3 dimensions. Depth, Width, and Height.

The required minium depth of the working space varies with voltage and in relation to grounded or energized components on the opposite side of the working space.  NEC Table 110.26(a)(1) describes the arrangements of 3 typical installations as conditions 1, 2, or 3.

Table11026

Where the voltage is equal to or less than 150 volts, 3-ft. is the minimum required working depth for all 3 conditions.  But at higher voltages, the depth varies for each condition.  For example, if a worker is exposed to energized parts while testing or servicing 480 volt switchgear and there are no energized or grounded parts on the opposite side of the working space, then it is a condition-1 situation and, the minimum required depth of the working space is 3-ft.

However, if the worker is exposed to bare energized parts on one side of the work space and grounded parts on the other side of the work space, such as a concrete or block wall, it is a condition-2 situation, and the minimum required depth is 3-ft. 6-in.  Brick, tile or concrete walls are considered to be grounded.  But if the worker is exposed to bare energized parts on both sides of the work space it is a condition-3 situation, and, the minimum required depth is 4-ft.

Regardless of the depth of the work space, the width of the work space is required to be at least 30-in. or the width of the equipment, whichever is greater.

The minimum height (headroom) is required to extend from the floor up to a height of 6 ½-ft. or the height of the equipment itself, whichever is greater.  There are two exceptions:  (1) In existing dwelling units, service equipment or panelboards that do not exceed 200 amperes.  (2) Meters that are installed in meter sockets shall be permitted to extend beyond the other equipment.

The minimum working space requirements in NEC Table 110.26(A)(1) are NOT required for the back and sides of equipment like dead-front switchboards, switchgear, or motor control centers where connections and renewable or adjustable components are not accessible from the back or sides of the equipment.


Review Question Section 3.9

23. What is the required work space depth in front of a 480 volt fusible disconnect where the wall opposite the disconnect is concrete block?


3.10 Large Equipment

NEC article 110.26(C)(2) defines Large Equipment as: Equipment rated 1200 amps or more and over 6 ft. wide.

The entrance and egress requirements for large equipment are strict because of the hazards workers face in the event of arc-flash accidents. Having ready access to an unobstructed means of egress (or way out) can be a matter of life or death in the event of catastrophic arc-flash incidents.

The switchgear in this illustration is Large Equipment in terms of both amperage and physical size. It is required to have a means of entrance and egress at each end of the working space unless one of two conditions is met:

  1. The means of egress is unobstructed or
  2. The depth of the working space is twice that required in Table 110.26(A)(1).

Although only one exit is visible in this illustration, another exit door also equipped with a panic bar is behind the camera.  A single exit door would be permitted if the work space in front of the switchgear is doubled.


Review Question Section 3.10

24. Which piece of equipment listed below is classified as large equipment?

Equipment over 6 ft. wide and rated 1200 amps or more is considered to be large equipment, and has special working space requirements.

3.11 Height of Working Space and Illumination
Working space is required to be illuminated and to have a minimum height of 6 1/2 feet.

Illumination of working space is required by NEC article 110.26(D). However, a separate lighting outlet is not required if the working space is illuminated by adjacent lighting. Lighting cannot be controlled by automatic means only, such as an occupancy sensor that does not have a manual override switch.

For example, if the electrical equipment were installed in a room where the work space were illuminated by general lighting in the room then no additional light is required. Regardless of the source of illumination, it is not permitted to be controlled only by automatic means such as an occupancy sensor. In this illustration illumination for the equipment is provided by an overhead fluorescent luminaire.

The minimum height of the working space in front of the equipment is 6½ feet or the height of the equipment, whichever is larger.  In this illustration the height of the workspace exceeds the minimum requirement of 6½ feet.  It is always acceptable to exceed the minimum requirements for work space height.

This illustration shows a large portable fan stored in the equipment room; but the fan is not within the required working space.  The rubber mat in front of the 2 large disconnects provides workers standing in front of the equipment with some insulation from the cement floor and also reminds workers to keep the working space clear of obstructions at all times.  Many facilities now outline the working space on the floor with paint or safety tape.


Review Question Section 3.11

25. What is the minimum height requirement at a 2000 ampere, 480 volt motor control center that 8 ft. tall?


3.12 Dedicated Equipment Space

Dedicated equipment space is a three dimensional space reserved for electrical equipment and dedicated to the installation.  Both indoor and outdoor equipment requires dedicated equipment space.  The length and width of the space is outlined by the footprint of the equipment at floor level or grade.

Dedicated space extends from the floor to a height of 6-ft. above the equipment or the structural ceiling, whichever is lower.  This space is set aside for conduit, cable tray, and other wiring methods to enter the equipment.  No HVAC piping or ductwork, plumbing, or other foreign systems or equipment are permitted to be in or pass through the dedicated space.

If foreign systems or piping are installed immediately above the dedicated space, these systems must include protective equipment to prevent any leaks or drips from entering the dedicated space.

For example, if the footprint of a 7-foot high MCC was 2-feet x 6-feet and the MCC was installed in a room with a 12-foot ceiling, the dedicated equipment space would extend from the top of the MCC, 5-feet to the structural ceiling.  Only electrical equipment associated with the MCC could be installed above the MCC.  However, if the MCC was installed in a high-bay location with 35-foot ceilings, foreign equipment and piping could be installed directly over the MCC provided it was at least 6-feet above the top and included protective equipment to prevent drips or leaks from entering the dedicated space.

As a note:  Drop ceilings are not considered structural ceilings.  Using the example above, if the drop ceiling is located at a height of 12-foot and the structural ceiling at 16-foot, the dedicated equipment space would extend from the top of the MCC, 5-feet to the drop ceiling.  Any foreign equipment as related to HVAC piping or ductwork, plumbing, etc. located in the space between the drop-ceiling and structural ceiling must include protective equipment to prevent drips or leaks from entering the dedicated space between the MCC and drop-ceiling.

In this illustration a drip pan is not required because the piping is routed around the dedicated space.


Review Question Section 3.12

26. Which statement best describes dedicate equipment space?

The insulated pipes in the photo are considered as a foreign system and are not permitted in the dedicated space above the switchgear. In this illustration a drip pan is not required because the piping is routed around the dedicated space.

3.13 Enclosure Selection
Match the outdoor or indoor Type of Enclosure to the conditions where the equipment will be located.

Enclosures for electrical equipment not over 600 volts, and not in hazardous locations are selected from NEC Table 110.28.  Equipment such as panelboards, switchboards, motor control centers, transfer switches, enclosed switches, and general-purpose transformers are some of the types of equipment whose enclosures can be selected from NEC Table 110.28.

Enclosures_Outdoor

Enclosures_Indoor

The table is divided into types of enclosures for outdoor use and indoor use.  None of the enclosures in the table are intended to protect against condensation, icing, corrosion, or contamination that may occur with the enclosure or enter via the conduit or unsealed openings.

Enclosure types are identified with numbers and letters, for example 3R, 3S, 4X and 6P.

Outdoor enclosures are intended to protect against such conditions as rain, snow, sleet, windblown dust, temporary submersion or even prolonged submersion.

Indoor enclosures are intended to protect against such conditions as falling liquids and light splashing, circulating dust, lint, fibers, and flyings, or oil and coolant seepage.

To select the right enclosure for the conditions where the equipment is located, find the X in the table that matches the conditions.  For example a type 3R outdoor enclosure will protect against rain, snow and sleet, but not against windblown dust.  A type 2 indoor enclosure will protect against falling dirt and falling liquids and light splashing, but not hosedown and splashing water.


Review Question Section 3.13

27. Which type of enclosure will protect electrical equipment from corrosive agents?


3.14 Over 600 Volts. Entrance and Access to Work Space

For rooms, vaults, or other areas where equipment rated over 600 volts is installed, the doors into the area must be at least 24-inches wide and 6½-feet high.

For Large Equipment (equipment more than 6-feet wide), an entrance is required at each end of the space unless means of egress (the exit path) is unobstructed or the depth of the working space is doubled as permitted in NEC article 110.33(A)(1)(a)&(b).

Personnel door intended for entry into and exit from the working space that are less than 25-feet from the work space are required to open in the direction of egress (the way out) and to be equipped with listed panic hardware that opens under pressure.

For example, the personnel door in this illustration is less than 25-feet from the switchgear work space; it opens in the direction of egress and is equipped with a panic bar rather than a knob.  Listed panic hardware is of critical importance to personnel who may be blinded or have severely burned hands resulting from an arc-flash incident.


Review Question Section 3.14

28. Two doors lead into a room where equipment rated over 600 volts is installed. One door is 18-feet from the work space, the other door is 30-feet from the work space. Which of the following statements is true?

Personnel doors within less than 25-feet of working space are required to have panic hardware.

3.15 Over 600 Volts. Working Space
Working space is required to be illuminated and to have a minimum height of 6 1/2 feet.

The minimum depth of clear working space in front of equipment rated over 600 volts is required when the equipment may be serviced, maintained or tested while energized.  The depth of the working space specified in NEC Table 110.34(A) varies with the voltage and whether or not grounded or energized components are on the side opposite the working space.  The table describes the variable as conditions 1, 2, and 3.

For example, on equipment where the voltage to ground is 2300-V, if there are no energized or grounded components on the opposite side of the working space it is a Condition-1 location. The minimum depth of the working space is 3-feet.

However, if the side opposite the energized components was grounded it becomes a Condition-2 location. The minimum depth of the working space is 4-feet. Note: As it was in Section 3.9 above, the NEC considers brick, tile and concrete walls to be grounded.

And, if both sides of the working space contain bare energized parts, it become a Condition-3 location; and the minimum depth of the working space is 5-feet.

If the voltage to ground for the equipment is rated between 2501 volts and 9000 volts the minimum depth of the working space is 4-feet for Condition-1; 5-feet for Condition-2; and 6-feet for Condition-3.

 


Review Question Section 3.15

29. As described in NEC Table 110.34(A), when there are exposed live parts on both sides of the working space, what is the minimum depth of clear working space in front of a grounded, 3-phase switchboard if the voltage to ground is 2400-V?