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Wiring and the NEC

wiring - tech
An electrical technician connects circuits in a junction box. (Photo: What Took You So Long? Productions)

Building electrical systems are designed to safely distribute electricity to various locations in a building in order to power electrical loads.  The proper design and installation of such systems is critical to ensuring the safety and reliability of electricity supply.  This is especially true in medical facilities, where safety and reliability are of exceptional importance.

Electricity is distributed using electrical wire, which physically connects electrical outlets and other loads to a building’s electrical supply.  Wires are conductors (they are able to carry electrical current), and in the case of most building installations, are made of copper covered in plastic insulation.

A number of other components are also essential to building electrical systems, including: electrical panels, switches, junction boxes and receptacles.  Wiring connects these various components to create electrical circuits with specific voltage and current characteristics, depending on the type of loads they support.

In most places, electrical codes are used to ensure safety and reliability.  Those codes prescribe specific criteria which must be met before a building’s electrical system is considered acceptable.  In the United States, the National Electric Code (NEC) is the predominate code, often being adopted by local authorities who then enforce the code through certified electrical inspectors and permitting processes.

This page discusses some of the technical aspects of building electrical systems – appropriate wiring types and other essential components, as well as some good wiring practices as given in the National Electric Code.  Emphasis will be given to health facility electrical systems including backup or alternative power systems, with IHFI electrical installations in Haiti used as examples.

 

IHFI Experience 

USAID’s Improving Health Facility Infrastructure (IHFI) Project has been working with Haiti’s Ministry of Health to install and refurbish electrical systems and backup power systems in clinics and hospitals around the country.  This work has focused on the installation of battery-based backup power systems designed to support critical healthcare loads and sensitive laboratory equipment.  IHFI’s work has also been extended to the upgrade of electrical infrastructure in key hospitals, including the country’s main teaching hospital in Port-au-Prince, Hôpital de l’Université d’Etat d’Haïti (State University Hospital of Haiti), or HUEH.  See examples of IHFI’s electrical installations:

Regardless of the nature of the electrical installation, IHFI has strived to institute the guidelines of the National Electric Code with respect to the design, materials and workmanship employed in each installation.  As electrical wiring in most Haitian hospitals lacks many fire hazard safeguards, IHFI has placed an emphasis on standard wiring techniques – e.g. proper organization, labeling and color designations – as well as standard design components – e.g. conduit, safety switches and junction boxes.

This critical approach has also been applied to IHFI’s own electrical work.  A recent review of previous IHFI battery backup systems made a number recommendations for improvement in-line with NEC standards, everything from system design to labelling and location.

Finally, IHFI has integrated modules on the National Electric Code into its technician training program.  This is an important factor in ensuring that electrical installations improve on a broad and long-term basis.  IHFI's NEC training materials may be found here.

 

Wiring 

Wiring Construction

The basic purpose of wiring is to carry electrical current.  The wiring sizes and ratings outlined in later sections are necessary considerations when choosing the proper wiring. Different wire sizes and ratings are designed to meet the demands of a wide range of applications, voltages and environments.  This diverse range of properties ultimately stems from the materials and construction of the wire.  Electrical codes and wire standards strive for a balance of safety, cost and efficiency when defining appropriate wiring types.

 wiring - solid  wiring - stranded
Solid conductor  Stranded conductor

Wires are constructed of a conductor surrounded by various layers of protective material.  Conductors may be either a single strand of metallic material or a number of strands together.  A simple representation of this basic solid vs. stranded design is shown in the adjacent figure.  These two basic types of construction can be used interchangeably; the cost of manufacturing is the main consideration when choosing solid vs. stranded construction.  For a given conductor material, it is the cross-sectional area of wire that determines its current-carrying capacity.  In this case of a stranded wire, it is the total area of the individual strands (not including gaps between strands) that determines carrying capacity.

The main components of an electrical wire are identified and described in the following figure and table.  The essential component is the conductor, which carries the electrical current.  The remaining components are in place to reduce the risk of fire or electrical shock and to protect the conductor from physical damage and oxidation.  For most low-voltage wiring, only a layer of insulation is required.  Medium voltage wires also require shielding and jackets.

 wiring - LV  wiring - MV
 Typical low-voltage (0-600V) wire construction Typical medium-voltage (2-35kV) wire construction 

 

Component/PurposeDescription
Conductor
  • carries electrical current
Copper is the most common material used in wire conductors.  Copper is advantageous because it has a very high electrical conductivity (low resistance) and is durable.  Aluminum is lighter weight and less expensive than copper, but will expand and contract with temperature changes, which can sometimes pose a fire hazard.  While both are generally accepted under electrical codes, copper is the more common choice for electrical installations.  For high-voltage, long-distance power transmission, aluminum is preferred due to its light weight and relatively low cost.
Coating/Plating
  • reduces oxidation in high heat
Copper wire may be coated or plated with another metal, commonly tin, silver or nickel.  While copper has a number of advantages that make it an excellent choice of conductor in wiring, certain applications may require wire with a slightly different set of properties.  The main purpose of plating a copper wire is to increase its resistance to oxidation, the degrading effect of air on bare wire, when used in a high-temperature environment.  Proper wiring designations for plated wire are specified in the NEC for certain applications.
Insulator
  • electrically isolates wire
  • reduces fire hazard
Wire insulators are plastic coverings that keep the conducting material electrically isolated, preventing short circuits, and inhibiting fires by limiting the amount of heat leaving the conductor.  Insulators are made of one of two types of plastics: thermoplastics or thermosets – compliant wiring will be marked with a designation of the insulation type.
Jackets
  • protects from physical and chemical damage
Jackets are an outer covering to the wiring insulation that provides enhanced protection against the environment, which may include: physical, chemical, fire and ultraviolet damage.  One or more insulated wires may be held in a jacket.  Jackets are also made of either a thermoplastic or thermoset.
Shielding
  • confines electrical field
Shielding is used in medium voltage (2-35kV) wiring to confine the conductor’s electrical field.  Shielding is made of a semi-conducting material and is placed between the cable’s conductor and insulation.  For cables rated over 5kV, an additional semi-conductor/metallic shielding layer is applied to the outside of the insulator.

 

Wiring Color

In an electrical circuit, various wires are used to serve different purposes.  For instance, in a single-phase AC circuit, three wires are used: a positive, a neutral and a ground wire.  The color of a wire’s insulation is used to designate its purpose in such a circuit; for example, ground wires are normally green or green-yellow.

Standard wire colors are partially determined by electrical codes.  Most codes, however, allow for alternative colors or do not specify a color for certain wires categories.  Furthermore, customary color designations vary locally.  Thus, there is no universal standard for wire color codes.

Wire color coding is a safety measure, meant to ensure that wires are properly identified when being handled.  For example, current carrying wires must be distinguished from grounding wires because a grounding wire is critical to preventing electrical shock.  The NEC distinguishes three basic categories of circuit wire (see the following table): grounding (leading to ground – protective earth), grounded (connected to a grounding wire - neutral) and ungrounded (not grounded or grounding – current carrying).

CategoryNEC colorExample
 Grounding  Green, green with yellow stripes or bare 800px-Wire green.svg800px-Wire green yellow stripe.svgColor wire bare copper.svg
 Grounded White, grey or white stripes 800px-Wire white.svg800px-Wire gray.svg800px-Wire gray white stripe.svg
 Ungrounded  Not specified 800px-Wire black.svg800px-Wire red.svg*

*typical convention in the United States

Wiring Size

The thickness of a wire, often referenced by its diameter, cross-sectional area, or “gauge”, is the central characteristic to determining the load, in amperes, that it can safely carry.  Thicker wiring can safely handle more amperes (i.e. more power) than thinner wiring.  This is why utility grid wires are thicker than household wiring, and why a refrigerator or air conditioner has a thicker cord than a lamp.

This is due to a basic physical property of conductors, called resistance.  Resistance is a measure of the amount of electrical energy that will be converted to heat as it moves through a conductor; wiring with lower resistance generates proportionally less heat than wiring with higher resistance.  As the cross-sectional area of a wire increases, its resistance decreases.

Undersized wiring is therefore a fire hazard, as thin wire carrying high amperage will generate a dangerous amount of heat.  In order to minimize the possibility of overheating, wiring sizes are standardized for specific amperage thresholds.  Two systems of measurement are used to specify wiring: the American Wire Gauge (AWG) and metric.

AWG

wiring - gauge size
Relative size of wires under the AWG sizing system.

The American Wire Gauge is a system developed and used primarily in the United States.  Wiring thickness is termed by its “gauge” and is referenced by a number from 0 to 40, with lower gauges having a greater cross-sectional area.  Note that even larger wires, those below guage 0 (1/0), are designated as 00 (2/0), 000 (3/0), 0000 (4/0).  For instance, a building’s service entrance (its electrical connection to the grid) usually requires 0, 1/0 or 2/0 gauge wire, while typical in-building branch circuits use 10 to 14 gauge wire.

Two types of units unique to wiring are a “mil” and a “circular mil”.  A mil is 1/1000 (0.001) inches, and is used to define the diameter of a wire.  A circular mil is a measure of the cross-sectional area of a wire, which in the case of a solid wire is simply the diameter (in mils) squared.  Note that a circular mil is not equivalent to the actual cross-sectional area in mils, but is an expedient way to reference the size of a wire.  Under the AWG system, wires larger than 4/0 gauge are specified in terms of circular mils.

Metric

Metric wiring designations are either the wire diameter in millimeters (mm), or the gauge, which is 10 times the diameter in mm (e.g. 2 mm, or 20 gauge).

Wire Ratings

Wiring standards use letter designations to indicate various characteristics of the wire, such as the insulation material and heat rating.  The following table presents a selection of some of the more common designations relevant to hospital wiring.  Note that there are many designations that are not listed here, as well as designations used only for particular standards, certifications and compliance codes.

Letter designationMeaning
T Thermoplastic insulation (e.g. PVC)
R Thermoset insulation (e.g. rubber)
H Rated to 75°C
HH Rated to 90°C
N Nylon jacket
W Moisture resistant

 

Rating typeDescription
Temperature Rating Temperature ratings are made separately for dry and wet conditions, with some wiring having the same temperature rating for both.  Unless marked otherwise, standard compliant wiring is rated to 60°C, although a 75°C rating is common.  A greater temperature rating is warranted when the environmental conditions necessitate, or when specified by local codes.  90°C is the highest wet rating, while dry ratings can reach 250°C.
Moisture Rating Moisture resistant wires are typically marked with a “W”.
Sunlight Resistance Wiring is not normally marked for sunlight resistance, although many wiring types are evaluated for their resistance to UV radiation.  Any wire with an overall metallic covering is suitable for exposure to sunlight.
Outdoor Use Wires rated to withstand outdoor conditions may be marked in a number of different ways.  In some cases ratings for sunlight resistance and wet conditions is enough to prove applicable to outdoor use.
Voltage Voltage ratings very widely depending on the application, as dictated by the NEC.  Many low-voltage wires, however, are rated at either 300VAC or 600VAC.  Medium-voltage wires are between 2.4kVAC and 25kVAC.
Cable Tray or Direct Burial Wires laid in cable trays or directly buried in the earth have special requirements in terms of moisture and fire resistance.  While certain wire types are rated specifically for such applications, they are generally not marked as such.

 

Building Circuits 

In building electrical systems, the term ‘branch circuits’ is used to describe the wiring that runs from the building’s electrical panel to outlets and other electrical loads around the building, connecting the utility or generator to the end-use devices.  These branch circuits must be designed to support the loads to which they are connected, which will dictate the rated ampacity of the wiring and circuit breaker.

Circuits must therefore be designed with the size and type of loads they power in mind.  Some circuits may power individual loads, such as air conditioners, washing machines and driers.  Larger loads such as these typically require a higher voltage, and those circuits must have a higher amperage capacity.  Most normal branch circuits are 15 or 20 amps.

Load Designation

Circuits that support sensitive electronic loads, such as computers or medical equipment, may require protection from an uninterruptable power supply (UPS) or other power conditioning equipment.  If such a device is hard wired into the circuit, that circuit is designated a no-contact circuit.  

Only sensitive equipment in need of protection from power quality problems should be placed on a no contact circuit, as unnecessary loading could over-load the device and take up valuable clean power from other sensitive equipment.  Labeling of outlets or receptacle color on a no contact circuit is useful to ensure that contact loads are not placed on the circuit.

Essential Components

A number of different components are needed to safely and efficiently distribute electricity in buildings.

ComponentDescription
Service entrance The service entrance is the point where the utility lines connect to the building’s electrical system.  This typically consists of high-amp, low-gauge wires running between the power line, the electricity meter and the building’s electrical panel.
Electricity meter A device that measures the amount of electricity, in kWh, used by a facility.  Normally owned by the electric utility, they are placed before the building’s main distribution panel.  Sub-metering is also possible, where in individual branch circuits are metered for their electricity consumption.
Wires (conductors) Wiring, or conductors, transfer electricity from one point to another, physically linking power supplies and loads.
Circuit breaker (C/B) A circuit breaker is a type of switch that allows for manual connect/disconnect of circuit loads as well as an automatic disconnect which is tripped when incoming power passes a specific amperage.
Branch circuit Branch circuits are the wiring between two or more electrical loads (e.g. outlets, lighting fixtures) and a circuit breaker or fuse.  Buildings typically have multiple branch circuits serving loads based on location, equipment type or power requirement (i.e. contact/no-contact loads).
Electrical panel or load center The electrical panel distributes the incoming power supply to branch circuits and also houses the circuit breaker or fuse protecting each (it may also be referred to as the breaker box or fuse box).  Electrical panels are usually located after the utility meter and are the first component interior to the building.
Bus bar A bus bar consists of a series of copper bars or tubes designed to distribute current to multiple branch circuits.  The advantage of a bus bar is flexibility and adaptability; because a bus bar is essentially a bare, rigid conductor, distribution components such as circuit breakers or fuses can be added, relocated or removed with ease.  Such components may attach to any point along the length of the bus bar’s structure, making electrical connection with the copper conductors.
Fuse Fuses, like circuit breakers, are designed to protect circuits from excess current.  The maximum amount of current any circuit can carry is dictated by the wiring gauge of that circuit; excess current may damage the wiring and is a fire hazard.  Fuses are designed to break when they are exposed to too great a current, thus protecting the circuit.  Unlike circuit breakers, fuses can only be used once and must be replaced.
Junction box A junction box is a metal or plastic enclosure used to protect wiring connections.  Junction boxes vary in their size and configuration depending on their purpose, although some common uses include electrical outlets and wall switches.
Switch

A switch is a simple device used to complete, or break a circuit.  A small conductor will physically connect two wires to complete a circuit, allowing current to flow, when the switch is on.  When off, the conductor physically disconnects from one of the wires, stopping the flow of electricity.

Switches serve many purposes in a building electrical system.  Wall switches are used to turn lighting on and off, for instance.  Circuit breakers are switches that control entire branch circuits, and safety switches may be used for many reasons at various points in a building’s electrical system.

Electrical outlet (receptacle) Electrical outlets provide connection points for various types of electrical devices, which are plugged into the outlet’s receptacles.  Standards for plug configuration differ worldwide.  
Conduit Conduits are a type of piping used to provide structure and protection to electrical wiring.  Conduits are typically made of metal or PVC plastic and may be rigid or flexible, depending on their application.  Use of wiring conduit is an important part of electrical safety and good practice, as well as code compliance.
Cable tray A cable tray is an open tray or rack that is designed to distribute building wiring while allowing easy access for repair, maintenance or addition.  Cable tray systems are usually attached to walls or ceilings.  Wiring used in a cable tray must be specially rated for fire protection.
Grounding system A grounding system comprises all of the components, mostly conductors, needed to properly ground or “earth” an electrical system and its non-current-conducting components (e.g. metallic junction boxes).  Components of the grounding system include:
  • grounding electrode – typically long copper rod driven into the ground, providing an electrical connection to the earth.
  • grounding electrode conductor – the wiring used to connect various parts of the electrical system or its non-current-carrying components to the grounding electrode
  • grounding conductor – a  conductor within the electrical system or circuit that is connected to ground.  In an AC system, this is the neutral wire.

 

wiring - meter wiring - load center wiring - jbox
Electricity meters continuously track power consumption - most utilities provide meters as they are essential to proper billing. (Photo: What Took You So Long? Productions) Electrical panels range in size depending on the number of branch circuits found in the building.  Seen here are the circuit breakers protecting each branch circuit. (Photo: What Took You So Long? Productions) A junction box is a simple housing used to protect electrical splices and connections, in this case an electrical outlet. (Photo: What Took You So Long? Productions)

 

 

Single-line Diagrams

A single-line diagram (or, one-line diagram) is a graphic representation of a facility’s electrical distribution system that shows how all electricity consuming equipment and distribution components are connected to the power supply.  Such diagrams are referred to as single-line diagrams because a single line is used to represent all the wiring of an AC or DC system (usually 3 to 5 wires).

Single-line diagrams are a standard format for designing and contracting electrical work.  A complete single-line will show all equipment used in the distribution and consumption of power, including ratings (e.g. circuit breakers/amp ratings).  As a means to facilitate additions and repairs to the distribution system, an up-to-date single-line diagram of a facility’s power system is an important part of the facility’s management and maintenance.

Single-line diagrams may also show only a portion of a power distribution system, as in the following figure, which shows a battery inverter system installed at an IHFI site in Haiti.

wiring - single line
This single-line diagram of an IHFI backup power system in Haiti is useful for identifying connections between major components.

 

The National Electric Code 

The National Electric Code is a standard electrical code used primarily throughout the United States.  The code is adopted by states and municipalities, either in its entirety or in a modified form.  The NEC is issued by the National Fire Protection Agency (NFPA) and is updated every three years.  The goal of the NEC, or any electrical code, is to reduce the hazards associated with electrical installations, such as fires and electrical shock, and to ensure the reliability of those installations.

While the NEC is not implemented universally, it does address the fundamental principles of safe electrical installations.  It is therefore generally in line with the International Electrotechnical Commission’s standard for electrical installations in buildings, IEC 60364.  Like the NEC in the United States, IEC 60364 is commonly used throughout Europe as a model which can be adapted to create local standards.

The NEC generally covers all electrical installations in buildings and outdoor areas such as parking lots, as well as any connection to an electrical supply.  Furthermore, the NEC addresses specific wiring and safety issues for a variety of specialty applications.  Discussed in greater detail below are three such applications that are directly relevant to healthcare and remote power.

Healthcare Facilities

The NEC’s requirements for healthcare facilities include general wiring guidance as well as special treatment for healthcare-specific applications like inhalation anesthetizing locations or x-ray installations.  Much of this section, however, covers essential electrical systems – those serving critical loads – emphasizing the importance of these two concepts in medical facilities.  

An essential electrical system comprises one or more alternative power sources (e.g. generators and battery banks) and the distribution network connecting them to their loads.  Such a system is required to provide continuous power to lighting and other loads essential for life safety during a power loss.  In fact, the NEC further subdivides the essential system’s loads into two separate systems – an equipment system that serves equipment deemed necessary to basic building operation, and an emergency system for loads critical to health and safety and patient care (called the “critical branch”, and the “life safety branch”, respectively).

The NEC guidance on essential electrical systems has been very important to IHFI installations in Haiti, especially those based on battery storage systems.  As most of IHFI’s installations are dedicated to providing backup power to critical loads, many represent the first instance of an essential electrical system being utilized at the facility.  Important features of these installations, as outlined in the code, include: electrically separate branch circuits for critical loads, mechanical protection through metal conduits for all essential systems, and identification of receptacles served by the backup power system.

wiring - wireinstall wiring - conduit wiring - contact
Electrical wiring is bundled together and labeled during installation. (Photo: What Took You So Long? Productions) Metal conduits and junction boxes are used to run all wiring throughout the facility.  The NEC requires metal conduit for wiring of "essential systems" in health facilities.  (Photo: What Took You So Long? Productions) Recepticals connected to circuits serving critical loads should be labeled to ensure that only designated equipment is suppored by the backup power source. (Photo: What Took You So Long? Productions)

 

Battery Systems

wiring - Inverters and batteries
Proper battery storage requires adequate ventilation and enough space to perform maintenance. (Photo: Kim Domptail)

NEC requirements regarding battery systems are relatively minimal and commonly refer to other Articles of the code with respect to wiring and over-current protection.  Much of the material under the Storage Batteries article covers battery storage and housing.  For example, the code lays out the electrical insulation requirements for different battery types and voltages.  Most significantly, the code mandates that battery banks are housed in racks and placed in well-ventilated locations that provide adequate room for service.  IHFI utilizes a standard battery rack design which protects the batteries, leaves room for ventilation, and raises them off of the floor (placing batteries on the ground depletes their charge).

PV Systems

As a PV module will produce power as long as it receives sunlight, it presents a special hazard to electrical technicians performing maintenance or repairs on connected circuits or electrical distribution networks.  Thus the NEC sets forth a number of requirements designed to isolate PV systems when necessary, to select and size fuses, breakers and conductors, and to accommodate the variable nature of their power output.

In the first place, the NEC provides standard definitions of PV system components (e.g. module, inverter) and configurations (i.e. AC module, interactive, hybrid, and stand-alone).  General safety guidelines regarding installation and labeling of PV system wiring and components are also presented.

As with any type of electrical installation, choosing appropriately sized components (e.g. conductors, fuses, switches) is essential to safety and efficiency.  Components are sized in terms of their rated voltage and amperage, and the code specifies how these voltage and amperage levels should be calculated and applied to various parts of the PV system.  For example, when determining a PV system’s maximum voltage, a temperature correction factor, specified by the code, is applied to the rated open circuit voltage of the panels based on the lowest expected ambient temperature.  A number of additional safety factors may be applied to this voltage, depending on which part of the system is under consideration.

Two components critical to the safety of a PV system are the disconnecting means and the grounding electrode.  

A disconnect switch is typically used to either a) disconnect power from a building’s branch circuits, or b) disconnect power to individual system components for maintenance.  The NEC sets forth specific requirements for the placement of disconnect switches in a PV system based on the system’s configuration.  Generally speaking, a disconnect switch is required on either side of the inverter (thus a DC disconnect and an AC disconnect are necessary).  This allows for inverter maintenance as well as a means to cut the PV power source from the building’s electrical panel.  Note that other system components such as batteries and generators also require separate disconnect switches.

Grounding requirements may be separated into two categories: equipment grounding (grounding non-current-carrying equipment such as PV module frames and racks and metallic equipment enclosures), and system grounding (grounding of the system’s electrical conductors).  Equipment grounding, otherwise known as safety grounding or protective earthing, is required by the NEC, but with a number of exceptions or additional guidelines for specific situations.  In general, all non-current-carrying metallic equipment must be grounded.  Methods for establishing such a grounding connection differ depending on the equipment type.  Most certified enclosures (such as for a disconnect switch, for example) provide a terminal or other means for connecting a grounding wire.  Module frames and racks should also be connected to the grounding system using a certified grounding devise (such as a grounding bolt).

 

Standards 

The standards listed below conform to the National Electric Code.  These standards, while not required explicitly by the NEC, are designed to ensure that their respective components meet NEC requirements.  While other international codes, such as IEC electrical codes, may differ in their requirements, these standards may still be viable.  Ultimately, the local electrical code will have final authority over which codes and standards are applicable.

 

Underwriters Laboratory (UL)
CategoryStandard
Wire/cable    UL 4: Standard for Armored Cable
Conduit UL 1: Standard for Flexible Metal Conduit
Other components UL 857: Busways
Wire/cable UL 83: Thermoplastic-Insulated Wires and Cables
Wire/cable UL 44: Thermoset-Insulated Wires and Cables
Enclosures UL 514A: Metallic Outlet Boxes
Conduit UL 514B: Conduit, Tubing, and Cable Fittings
Enclosures UL 514C: Standard for Nonmetallic Outlet Boxes, Flush-Device Boxes, and Covers
Enclosures UL 514D: Cover Plates for Flush-Mounted Wiring Devices
Conduit UL 651: Standard for Schedule 40 and 80 Rigid PVC Conduit and Fittings
Conduit UL 651A: Type EB and A Rigid PVC Conduit and HDPE Conduit
Conduit UL 1242: Standard for Electrical Intermediate Metal Conduit - Steel
Conduit UL 797: Standard for Electrical Metallic Tubing - Steel
Conduit UL 797A: Standard for Electrical Metallic Tubing - Aluminum
Conduit UL 1653: Electrical Nonmetallic Tubing
Conduit UL 6: Electrical Rigid Metal Conduit - Steel
Other components UL 924: Standard for Emergency Lighting and Power Equipment
Enclosures UL 50: Standard for Enclosures for Electrical Equipment
Wire/cable UL 62: Flexible Cords and Cables
Other components UL 20: General-Use Snap Switches
Other components UL 934: Standard for Safety for Ground-Fault Circuit-Interrupters
Other components UL 467: Standard for Grounding and Bonding Equipment
Conduit UL 2239: Hardware for the Support of Conduit, Tubing, and Cable
Other components UL 1741: Standard for Inverters, Converters, Controllers and Interconnection System Equipment for Use With Distributed Energy Resources
Other components UL 1047: Standard for Isolated Power Systems Equipment
Conduit UL 1660: Liquid-Tight Flexible Nonmetallic Conduit
Conduit UL 360: Standard for Liquid-Tight Flexible Metal Conduit
Other components UL 248 (Parts 1-16): Low-Voltage Fuses
Other components UL 60601-1: Medical Electrical Equipment, Part 1: General Requirements for Safety
Other components UL 67: Standard for Panelboards
Other components UL 231: Standard for Power Outlets
Wire/cable UL 1581: Reference Standard for Electrical Wires, Cables, and Flexible Cords
Wire/cable UL 854: Standard for Service-Entrance Cables
Other components UL 1008: Standard for Transfer Switch Equipment
Other components UL 486A-B: Wire Connectors

 

American Society for Testing and Materials (ASTM)
CategoryStandard
Terms ASTM E772 - 11: Standard Terminology of Solar Energy Conversion
Test ASTM E2848 - 11: Standard Test Method for Reporting Photovoltaic Non Concentrator System Performance

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