1 LBNL Electrical Equipment Build Standard V6.pdf

LBNL Electrical Equipment Build Standard Revision 6

1 Introduction The design and fabrication requirements in this document are derived from many sources, including American National Standards Institute (ANSI) standards, National Fire Protection Association (NFPA) standards, the Occupational Safety & Health Administration (OSHA), the National Electrical Code (NEC) and LBNL Electronics Engineering Division best engineering practices. These design and fabrication requirements are intended to cover most electrical equipment but cannot be expected to comprehensively cover all equipment and all existing standards. Underwriters Laboratories (UL) standards are cited in many places and have been chosen to serve as best engineering practices because of their appropriateness and UL’s status as an NRTL accepted by OSHA. Where there are conflicts between this document and the National Electrical Code, the NEC take precedence.

1.1 Purpose

The purpose of these requirements is to identify a broad set of general design elements and principles that incorporate safe electrical design—that is, reduce the risk of electric shock and fire. These requirements are a consensus set of requirements that come from the sources listed above and approved by the Electronics Engineering Division Leaders and Department Head.

The requirements in this document cover many aspects of electrical design and fabrication, including:

a) Guarding of live parts

b) Adequate wire size

c) Grounding and bonding

d) Component selection and mounting

e) Equipment installation

These requirements are conservative in order to assure safety throughout the lifetime of the equipment, under varying conditions, and during fault conditions.

1.2 References

References to standards and codes used in this document can be found in the References section of this document. Works cited are denoted by a number in brackets, ie. [1].

1.3 Additional Information

This standard addresses many electrical safety issues that may be encountered during the engineering and assembly of electronic equipment. Additional information can be found in the appendices of this document.

1.4 Issues

Design issues that are not covered adequately by the requirements in this document shall be resolved by applying good engineering processes. In other words, the design shall be reviewed with the appropriate level of formality graded by the risk in the system.

Personnel requiring assistance should contact the Engineering Division for help.

1.5 Scope

This document provides safety criteria for equipment which is designed / built for research use which may include the modification of new, used, and donated equipment, at all LBNL laboratories, field sites, and outpost locations. This standard shall be applied to ensure the safety of all faculty, staff, and students, freedom from recognized hazards, and suitability for use. Equipment, which as a complete unit has obtained a UL® label, or similar listing from a nationally recognized testing laboratory (NRTL) is outside the scope of this document.

This document does not apply to the LBNL electrical distribution infrastructure.

1.6 General

1.6.1 Origination Area and Responsibility

The origin and maintenance of this document is the responsibility of the LBNL Engineering Division.

1.6.2 Authorization

This document was approved and adopted by the LBNL Engineering Division through a collaboration with the EH&S Electrical Safety Officer.

1.6.3 Compliance

Compliance with this document is the responsibility of the equipment owner. All applicable new equipment shall be inspected through the EESP program prior to use.

1.6.4 Deviation

Any deviation from the requirements of this document must have prior approval from the AHJ for research and scientific electronic equipment. Deviations must not pose a risk to the safety of faculty, staff, or students, or result in noncompliance with any legal requirements.

1.6.5 Requirements

The requirements of this document are supplementary to the referenced external standards (found in the References section). Compliance with this document does not guarantee conformance with any external standards. Equipment shall comply with applicable portions of the latest revisions of the National Electrical Code© (NEC) and the Occupational Health and Safety Administration (OSHA) standards.

1.7 Terms and Definitions

Approved: Acceptable to the Authority Having Jurisdiction (AHJ).

Authority Having Jurisdiction (AHJ): Generally, an organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure.

Cable Tray System: A unit or assembly of units or sections and associated fittings forming a structural system used to securely fasten or support cables and raceways.

Critical Components: Electrical components or assemblies used in a power or safety circuit whose proper operation is essential to the safe performance of the system or circuit.

EESP: A program for examining and approving electrical equipment and installations at LBNL. For more information, see PUB 3000, Chapter 14, Electrical Equipment Safety Program.

Conditions of use: Documented requirements for use of electrical equipment and components that must be met for the listing to be valid.

Listed: Electrical utilization equipment and components are “Listed” if it is of a kind mentioned in a list that is published by a Nationally Recognized Testing Laboratory (NRTL) that (1) makes periodic inspection of the production of such equipment and (2) states that such equipment meets nationally recognized standards or has been tested and found safe for use in a specified manner.

Live part: A part that can be energized to 50 V or greater during any phase of equipment operation.

May: Statements are generally used in statements that implement a “shall”, “must” or “should” but have additional option for further action or steps. It may also be used to indicate allowable alternatives.

Metal Wireways: Sheet metal troughs with hinged or removable covers for housing and protecting electrical wires and cable and in which conductors are laid in place after the wireway has been installed as a complete system (NFPA 70, 376.2).

Must: Statements implement LBNL policy. Exemption could be granted by the AHJ for research and scientific electronic equipment.

NRTL: Nationally Recognized Testing Laboratory. One of several organizations accepted by OSHA to inspect and approve electrical equipment. UL is the largest of the NRTLs.

Raceway: An enclosed channel of metal or nonmetallic materials designed expressly for holding wires, cables, or busbars. Raceways include, but are not limited to, rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, liquidtight flexible conduit, flexible metallic tubing, flexible metal conduit, electrical nonmetallic tubing, electrical metallic tubing, underfloor raceways, cellular concrete floor raceways, cellular metal floor raceways, surface raceways, wireways, and busways.

Recognized: An electrical component or piece of equipment that has been determined by UL or other Recognized NRTL to be acceptable provided it is used in accordance with conditions of acceptability.

Risk: The quantitative or qualitative expression of possible loss that considers both the probability that a hazard will cause harm and the consequences of that event.

Shall: Statements implement applicable regulation from standards and codes.

Shock hazard: Exposure during any phase of operations, normal and off-normal, to 50 V or greater.

Should: Statements are generally considered to be management directives, best practices or safest methods at the time the implementing document was developed. Exemption may require written technical justification.

2 Design Requirements

2.1 Diagrams

Electrical systems diagrams shall be provided. They should include but are not limited to the following information.

2.1.1 Conductors

Drawings shall show:

a) All conductors and wire size

Drawings should show:

a) Conductor color and identification (may follow applicable code standard).

b) Multiconductor cables with color code used, the number of conductors used, and the AWG or Metric size, e.g., 20 / #18.

2.1.2 Components (Devices)

Components shall be:

a) Identified on the drawing to match the equipment.

b) Shown with all wiring connections.

Note: Internal wiring of subassemblies may be shown on separate drawings.

2.1.3 Terminals

Terminal boards and terminal connections shall be identified.

2.1.4 Contacts

Where switches, relays, contactors, motor starters, etc., are used, their contact position (normally open, normally closed, etc.) with all utilities off shall be indicated.

2.1.5 Thermal Overloads

A thermal overload is a device to protect an electrical device like a motor/generator from catching fire/burning out due to excessive heat produced during operation. The thermal overload location in power and/or control circuits, including size and rating should be shown.

2.1.6 Breakers

The location of breakers or power feeds, including size and rating should be shown.

2.1.7 Function

The function of all switches and control devices shall be shown.

2.1.8 Motors

Size (watts/horsepower) and function shall be indicated.

2.1.9 Power Requirements

Supply voltage, phase, frequency and amperage shall be shown.

2.1.10 Symbols

The symbols shown in electrical systems diagrams should be National Equipment Manufacturers’ Association (NEMA) electrical symbols or ANSI/IEEE 315.

Unique symbols shall be identified and explained.

2.1.11 Component Specifications

All components (circuit breakers, transformers, fuses, etc.) shall indicate applicable values, e.g., current interrupt capacity, amperage, voltage, kVA.

2.1.12 Convenience Outlets

Convenience Outlets should be represented by a NEMA configuration indicating voltage, amperage, and grounding. If located in a potentially wet area, it shall be GFCI Protected.

2.1.13 Grounding (EARTH)

The main grounding conductor and all component grounding conductors shall be shown.

2.1.14 Calibration Points

All test points requiring power for tests or adjustments shall be shown.

2.2 Arc Flash

Personal Protection Equipment (PPE) exists to provide heat protection from an arc flash up to 40 cal/cm2. PPE is unable to protect a worker above this level. Any potential arc flash hazard above 40 cal/cm2 represents an extreme danger. Engineering solutions must be employed to provide the greatest margin of safety to personnel and reduce the arc discharge duration for any arc flash hazards to the lowest potential achievable.

Refer to the Arc Flash Hazard chapter of the LBNL Electrical Safety manual located in PUB 3000, Chapter 8, Electrical Safety Program.

2.2.1 Incident Energy Analysis

The incident energy analysis is the calculation of arc flash incident energy by competent engineering persons for a circuit, panel, or system. An incident energy analysis shall be performed for electrical panels whenever a new electrical service is provided or whenever the electrical load changes with respect to a previous arc flash calculation.

IEEE 1584 std shall be used to calculate incident energy and arc flash protection boundary for: 208V to 15kV; 3 phase; 50 Hz to 60 Hz; 700A to 106,000A short circuit current; and 13mm to 152 mm conductor gaps.

The “table method” of NFPA 70E-2012 Article 130.7(C)(15) shall not be used.

2.2.2 Electrical Disconnect

Equipment should be designed so that the equipment has an arc-flash rating of

1.2 cal/cm2 or less at the electrical disconnect.

2.2.3 Maximum Arc Flash Hazard

Electrical panels shall be designed in such a way as to minimize arc flash hazards and specifically eliminate any panels with arc flash hazards above 40 cal/cm2.

2.2.4 Energization Validation & Authorization Package (EVAP)

Required for all systems capable of producing an arc flash hazard. Refer to table 2.3.3 in the Electrical Safety Program.

To establish readiness for energization, a set of Energization Validation & Authorization Package (EVAP) documents must be assembled by the Responsible Individual (RI). This Work Planning and Control document package is required before new or modified equipment is energized. Each EVAP must be reviewed and approved by all applicable Electrical AHJs: Safe Work Practices, Safe Installations, and Safe

Equipment. The EVAP is required for minor to complex work with adherence to LBNL’s Integrated Safety Management (ISM) policy and PUB 3000.

The RI must provide Facilities Department an estimate of the expected load to identify the source of power for the equipment to be installed. The Facilities Department will provide the RI with single line drawing that includes the breaker identification and panel schedules to be documented in the electrical schematics.

The EVAP package must be reviewed and approved prior to energization and must include the following documents:

a) Required field test procedure, third-party test results and factory test documents with recorded results pertinent to the equipment to be energized.

b) A statement of record from the subcontractor or Berkeley Lab performing craft shop certifying that the work is complete, is in compliance with code and subcontract, and is safe to energize.

c) Required field inspection reports, which shall include verification of an NRTL listing or label, or field examination (Electrical Equipment Safety Program survey) is complete; equipment identification numbers and protective devices are set; and appropriate arc-flash labels are applied.

d) Legible electrical schematics and Facilities Department single-line drawing(s) marked to reflect the equipment to be energized with breaker identification and panel schedules pertinent to the equipment to be energized in accordance with planning the work.

e) A procedure to control hazardous energy in a step-by-step Method of Procedure (MOP) written to detail the steps applied to isolate (shut down)/deactivate and activate when energizing new or modified electrical wiring and equipment installations.

f) Work authorizations for Lockout/Tagout (LOTO) as applicable to energize the electrical equipment, and safety trainings for performing the work.

g) A validation memorandum from the Compliance Engineer that the aforementioned documents are complete and crosschecked for accuracy; test and inspection results are acceptable; and equipment is ready to energize.

The RI is responsible for requesting the services of a Compliance Engineer or Inspector of Record (IOR). Access the Facilities website and start a work order by requesting a service and selecting “Electrical Installations Inspections”. The Facilities WPC Planner will determine the need for an IAHJ Review document given the project scope definition. An IOR will be assigned to respond to the work order submitted by the RI.

The request for the inspection should be made at least 1 week prior to expected energization.

The details of the EVAP process can be found as a reference in PUB3000, Chapter 8, Electrical Safety Program, Reference Documents, Safe Electrical Installations Policy or in the LBNL Requirements and Policies Manual (RPM) under the Safe Electrical Installations Policy, IJHA Processes.

2.3 Components

2.3.1 Component Selection

a) Whenever possible, components should be NRTL-listed.

b) Recognized components are acceptable also. Recognized components must be used in accordance with the conditions identified in the listing.

c) Conditions of usage include factors such as temperature, environment, available fault current, and so forth. These conditions will be included in the documentation for the component.

d) Components that are not listed or recognized shall be evaluated for their safety and suitability. If the application involves a significant safety hazard or function, then the suitability of the component should be documented in a Safety Note.

e) Critical components must be listed or protected by a fuse. Critical components or assemblies include but are not limited to the following:

(1) All electrical components acting as protective device to interrupt current in an abnormal condition, such as circuit breakers, circuit protectors, fuses, and overload or thermal relays

(2) All components and wiring for the emergency stop system, including power supply, emergency stop contactor, or interrupting device and pushbuttons

(3) All hardware or firmware components and wiring for safety interlock circuits

(4) All devices that are in an area that is classified as a Hazardous Location with the appropriate rating for the area, such as Class I, Division 1 or Class I, Division 2, unless listed as intrinsically safe

(5) Those components that upon evaluation present a risk of fire or shock in their use or application

Note: It is possible and understood that like components can exist on equipment where one is required to be approved (listed) since it is used in a safety circuit or other device as described in the preceding list, and the other is not used in such a circuit. In these cases, like components are treated differently.

2.3.2 Electrical Disconnect

Equipment should be designed so that the contribution of all equipment at the electrical disconnect has an arc-flash rating of Category 0.

3 Fabrication Requirements

3.1 General Construction

3.1.1 Enclosures

Enclosures must be of substantial construction so as to avoid the likelihood of damage during normal use. Guidance on case thickness is found in UL Standard 508, Table 6.1 for steel and Table 6.2 for aluminum.

In addition, the following criteria should be considered, as appropriate:

a) Provide adequate conductivity to minimize shock hazard for maximum credible ground fault current. Alternatively, enclosures can be insulated to eliminate the shock hazard.

b) Contain explosive concussion and shrapnel resulting from arc blast or structural failure of electrical components. A capacitor failure is an example.

c) Provide the appropriate protection for the environment where the equipment will be used, e.g., outdoors, with explosive gases, in a corrosive atmosphere, etc.

d) Enclosures must be free of sharp edges.

e) No parts that can be contacted by the user should be sharp enough to cause injury.

f) No parts that are in areas likely to be serviced and are easily contacted by service persons should be sharp enough to cause injury.

g) No sharp edges, burrs, threads, etc. should be in contact with conductors.

Additional protection may be applied to conductors to protect insulation [1].

h) Wood or other combustible material should not be used as a mounting surface for electrical components.

Equipment intended for outdoor use must be enclosed in a NEMA 4X enclosure and must be labeled “For Outdoor Use”.

3.1.2 Penetrations

a) Enclosures must not have open knockouts or holes that allow workers to contact energized parts.

b) Holes that are 1/4 in. diameter or smaller provide adequate protection from energized parts. For openings larger than 1/4 in. refer to Openings in Enclosure in UL508 or Accessibility of Live Parts in UL508A.

3.2 Mechanical Assembly

3.2.1 Mounting

Components shall be mounted in accordance with the following requirements:

a) Components shall be located for ease of maintenance.

b) Components requiring periodic adjustments shall be readily accessible without disassembly.

c) Components requiring adjustment, calibration, testing, or service with power on shall have external test points, insulated potentiometer extensions, etc. to minimize exposure.

d) Switches, lamp holders, and the like shall be securely mounted.

e) All keyed devices shall be correctly seated in keyways.

3.2.2 Fastening

All components must be securely fastened. Observe the following fastening guidelines:

a) Do not depend on gravity or friction to keep components in place.

b) Devices shall not easily loosen by hand.

c) Fastening hardware should be of the self-clinching, self-locking or captive type.

d) Devices that are position-dependent, such as toggle and rotary switches must not rotate out of position.

e) Ceramic and ceramic-coated parts shall be mounted with nylon or fiber washers in contact with the ceramic surfaces. Resilient washers are used whenever brittle materials are bolted in an assembly.

f) There should be at least one thread visible beyond the front of a nut when threaded hardware is used.

g) Split or internal-tooth lock washers should be used when self-locking screws or nuts are not available.

3.2.3 Corrosion protection

Corrosion protection must be considered in all environments to maintain electrical integrity. Examples of environmental conditions where corrosion protection must be considered include high humidity and presence of corrosive vapors or other water sources within 6’ of assembly.

3.2.4 Marking

a) Electronic equipment should be marked with the following information

(1) Product name

(2) Manufacturers name (LBNL)

(3) The electrical schematic drawing number

(4) Serial number

(5) Electrical ratings

(6) Mechanical ratings (as applicable)

b) Component designation shall be plainly indicated with the same designation as shown on the diagram on the back plate of the assembly and must not be removable or located on the components.

c) Emergency Shutoff (EMO) devices shall be red with a mushroom head with a yellow background and be of the latching type. EMO devices shall be marked “Emergency Off” or “Emergency Shutoff” and must be able to be actuated with the palm of the hand.

d) Terminal boards and junction boxes located on units outside recognized power compartments, with potentials greater than 50 V, shall be labeled to clearly indicate the voltages present.

3.2.5 Recommendations

Enclosures should have:

a) A removable noncombustible panel for component mounting.

b) Hinged doors that swing horizontally and open a minimum of 165 degrees.

c) The depth of the working space in the direction of live parts shall not be less than 36”. The work space shall be clear and extend from the grade, floor, or platform to a height of 2.0 m (61⁄2 ft) or the height of the equipment, whichever is greater.

3.2.6 Restrictions

Enclosures shall not have any:

a) Components mounted on hinged doors or removable covers.

EXCEPTION: Control circuit components for operator use such as indicators, push buttons, etc.

b) Piping containing air, gas, or liquids.

EXCEPTION: Assemblies requiring liquid cooling may contain piping to carry the coolant to the components.

c) Unused or ineffectively closed openings.

3.2.7 Access

Enclosures shall be provided with access covers or doors that meet the following requirements:

a) Covers or doors that allow access to hazardous potentials shall require a tool to open or shall be interlocked and must have a Hazard Warning label installed.

b) Covers or doors with an area of more than 3 ft2 should be hinged.

3.2.8 Main Electrical Control Enclosure

When equipment geometry dictates a need for more than one power and power control device enclosure, the main electrical control enclosure shall:

a) Contain main supply circuit disconnecting means.

b) Contain all components and circuits that have hazardous potentials after the operation of the EMO switch(es).

c) Require a tool to open or be mechanically or electrically interlocked, or both, with the control enclosure doors so that none of the doors open unless the power is disconnected. Interlocking shall be reactivated automatically when all the doors are closed. A general electrical panel key alone is not acceptable.

3.2.9 Shields

a) Shields shall be of sturdy construction and should be provided with holes for inserting probes.

b) Shields shall not support combustion. Plastic is an acceptable material when temperatures will not deform the shield.

c) Shields shall be easily removed and replaced by service personnel.

d) Shields shall be securely mounted independently of components, i.e., removal of a shield shall not loosen components or devices.

e) Electrical shields shall not be conductive.

f) Lacquer, enamel, sealing compounds, paper, or cotton shall not be used in place of a shield.

g) Shields shall not be in contact with electrical conductors.

3.3 Bonding/Grounding

“Equipment grounding” generally refers to the connection of the equipment to the electrical system equipment-grounding conductor. “Bonding” generally refers to the practice of establishing electrical continuity between all exposed metal surfaces such that there is no potential between any two surfaces.

3.3.1 Grounding requirements

a) Only one conductor shall be terminated in a grounding connector.

b) All grounding and bonding wires shall be attached by dedicated means.

c) The hardware used for grounding or bonding shall not have any other purpose.

d) A grounding buss is recommended with individual grounding points.

e) The main grounding conductor shall be secured to a single designated termination point that will not be disturbed by any other conductor terminations.

f) A grounding conductor that enters the equipment shall be terminated in a pressure wire connector that is clearly marked as a grounding connection.

g) When terminal lugs are used for grounding, they shall be a ring lug type.

h) Sheet metal screws or connections that depend solely on solder shall not be used for grounding or bonding purposes.

Exception: The ground terminal on a power inlet module may be soldered provided that the terminal was designed for a solder connection and the wire connection to the soldering post is mechanically secure before soldering.

i) All grounding circuits within equipment shall ensure a resistance of one tenth ohm (0.1 W) or less at any point.

j) Grounding conductors shall be green, green with a yellow tracer, or bare copper wire or braid or have a clear jacket over copper.

k) All grounding conductors shall be stranded copper wire.

l) Grounding conductors and connectors shall be compatible in current rating to the associated ungrounded conductors and connectors.

m) The grounding conductors shall be unspliced and continuous from termination to termination.

n) Equipment ground must be run with circuit conductors ie. electrical cords.

o) All grounded equipment shall have the equipment ground conductor contained in the same raceway or cable as the ac circuit supplying the equipment.

p) It is permissible to have additional grounding electrode connections to equipment as long as all conditions listed in this subsection are met. It is not permissible to ground equipment only to a driven rod or other electrode and disconnect the ground from the ac branch circuit.

q) Grounds are not allowed to be daisy chained.

3.3.2 Bonding requirements

a) Bonding wires must be securely terminated.

b) All metal not carrying a current must be properly bonded.

c) All exposed metal parts must be positively bonded to one another.

d) Surface contact of anodized aluminum is not acceptable for grounding and bonding. The anodizing must be stripped away to allow adequate electrical contact, or a bonding wire must be installed between anodized surfaces.

e) An external tooth lock washer may be installed between the grounding lug and surface to be grounded to maintain the position of the lug and to insure effective penetration through any dirt or corrosion on the contact surface.

f) Metal surfaces that are securely bolted together are considered bonded if:

(1) Sufficient area between the surfaces is clean of paint and other coatings to ensure good metal-to-metal contact

(2) Bolt heads and nuts/washers are fully in contact with clean, uncoated metal surfaces

g) Any enclosure containing electrical conductors shall have an internal copper bonding wire installed between the panel intended for access by the user and a bonded surface.

h) A hinge does not constitute bonding unless it is listed by an NRTL or recognized for this purpose.

i) Connections that depend on friction are not acceptable for grounding or bonding.

Exception: Listed pressure connectors such as an insulated female wire disconnect (aka, Push-on terminal, FASTON) may be used to terminate wires on a power inlet module when the module is designed for such use.

j) Bonding Self Taping Screws are not allowed to be used as a grounding point. A Bolt with washer and Nut must be used or a Grounding Buss Bar installed.

k) If a control panel has any Human Interfaces (buttons, switches or lamps) the control panel must be grounded.

3.4 Accessibility of Live Parts

a) No parts intended to be accessible to unauthorized employees shall be energized to >50 vac or >100 VDC and >5 mA or 10 J stored energy. This applies to holes in a chassis, connectors where conductors are not sufficiently recessed, and panels that may be opened without tools.

b) Shrink tubing cannot be used as a primary barrier for exposed voltages >50 V unless it has been listed for that purpose.

c) Electrical equipment should be designed so that routine maintenance can be done without having workers exposed to live parts. A Lock Out point may be required and must be identified.

d) If an enclosure employs a cover that can only be removed with a tool, and if live parts are accessible when the cover is removed—that is, when the cover is not interlocked—then the cover shall be so marked.

e) Enclosures accessible without using tools shall either be interlocked so that live parts are de-energized when the enclosure is opened or there must be no exposed live parts.

f) Interlocks may be implemented in software provided failsafe design principles are followed.

g) Failsafe means that loss of power, power supply failure, broken or disconnected wires, communications failure, CPU failure, and so forth should all be interpreted as unsafe conditions and the hazardous conditions eliminated.

h) Communications and CPU failure often require specific design features such as watchdog timers. The methods used to assure failsafe performance are examples of topics that should be included in a Safety Note.

i) Front panels shall be electrically dead, including during fault conditions

3.5 Indicator Lights and Lighted Switches

Indicator lights and lighted switches shall meet the following requirements:

a) Indicator lights and lighted switches shall be restricted to 120 V, maximum.

b) Should be installed in 24 V circuits or have voltage reducing devices in the light assembly that limits the bulb voltage to 24 V maximum.

Exception: Neon lights.

c) Where multiple bulb socket assemblies are used, the bulbs should be rated for not more than 24 V and should be connected in parallel.

d) Two-terminal lamp sockets shall be wired with the shell terminal connected to the grounded conductor.

e) Indicators and switches shall be labeled for their function.

f) Exposed parts, including mounting hardware, shall be grounded, of insulating material, or be adequately covered by insulating material.

g) Indicator light circuits used for warning or danger lights shall be fitted with facilities to check the operability of these lights.

h) Indicators must comply with the colors in Table 1

(1) The use of red, yellow, green or blue indicators for functions other that what is specified in Table 1 must be documented in a Safety Note and archived in the Document Control Center.

(2) Other indicators may be any other color.

(3) Green may be used when white is not available.

(4) Flashing indicating lights may be used when the application requires a more compelling indication.

Color Safety of Persons or

Environment Condition of Process State of Equipment

Red Danger Emergency Faulty Yellow (Amber)

Warning/Caution Abnormal Abnormal

Green Safe Normal Normal Blue Mandatory Action Mandatory Action Mandatory Action

White No specific meaning assigned No specific meaning assigned

No specific meaning assigned

Table 1, Machine Indicator Lights and Icons (NFPA 79, table 10.3.2)

3.6 Internal Wiring

3.6.1 Conductors

a) Conductors shall be selected for the operating conditions and external influences that can exist.

b) Conductors shall be compatible with the device terminal(s), and the conductor size shall not exceed the range recommended by the device manufacturer.

c) The ampacities of conductors shall not exceed the corresponding temperature values given in Table 2 before any correction factors for ambient temperature or adjustment factors for the number of current-carrying conductors have been applied.

d) Conductor Ampacity given in Table 2 Based on Copper Conductors with 60°C (140°F), 75°C (167°F), and 90°C (194°F) Insulation in an Ambient Temperature of 30°C (86°F).

e) Where ampacity derating is required for ambient temperature correction for other than 30°C (86°F) or adjusted for more than three current-carrying conductors in a raceway or cable, the factor(s) shall be taken from Table 3 and Table 4. Sizing of conductors within control enclosures in wiring harnesses or wiring channels shall be based on the ampacity in cable or raceway. These factors shall apply to NFPA 70, Article 725, Class 1, control conductors, only if their continuous load exceeds 10 percent of the conductor ampacity.

Conductor Size

Conductor Ampacity Based on Copper Conductors with 60°C (140°F), 75°C (167°F), and 90°C (194°F) Insulation in an Ambient Temperature of 30°C (86°F)

(AWG) 60°C (140°F) 75°C (167°F) 90°C (194°F)

30 — 0.5 0.5 28 — 0.8 0.8 26 — 1 1 24 2 2 2 22 3 3 3 20 5 5 5 18 7 7 14 16 10 10 18 14 20 20 25 12 25 25 30 10 30 35 40 8 40 50 55 6 55 65 75 4 70 85 95 3 85 100 110 2 95 115 130 1 110 130 150

1/0 125 150 170 2/0 145 175 195 3/0 165 200 225 4/0 195 230 260 250 215 255 290 300 240 285 320 350 260 310 350 400 280 335 380 500 320 380 430 600 355 420 475 700 385 460 520 750 400 475 535 800 410 490 555 900 435 520 585 1000 455 545 615

Table 2, Conductor Ampacity (NFPA 79, table 12.5.1)

Ambient Temperature

(°C) Correction Factor

Ambient Temperature

(°F) 21–25 1.05 70–77 26–30 1 78–86 31–35 0.94 87–95 36–40 0.88 96–104 41–45 0.82 105–113 46–50 0.75 114–122 51–55 0.67 123–131 56–60 0.58 132–140 61–70 0.33 141–158

Table 3, Ambient Temperature Correction Factors (NFPA 79, table 12.5.5)

Number of Current-Carrying Conductors

Percent of Values in Table 3 as

Adjusted for Ambient Temperature

If Ambient Temperature If Necessary 4–6 80 7–9 70

10–20 50 21–30 45 31–40 40

41 and above 35

Table 4, Adjustment Factors (NFPA 79, table 12.5.5(b))

3.6.2 Terminals

Terminals shall comply with the following:

a) There shall be no unshielded terminals having hazardous potentials or hazardous energy levels external to control enclosures, compartments, or junction boxes.

b) Terminals should be sized and used in accordance with Table 4.

c) Terminals on terminal blocks should be numbered in ascending order from top to bottom or from left to right.

d) There shall not be more than two conductors per lug and two lugs per termination.

e) Terminals shall retain conductor strands without damaging the conductor.

f) Approved terminal lugs shall be used to connect conductors to component terminals which are not equipped with wire clamps, pressure plates or equivalent means of retaining conductor strands.

Screw Size Amperage

(Terminals Per Screw)

Maximum

Conductor

Size Metric NC/NF One Two AWG mm2

M3 — 10.0 7.0 14 1.5

— 5-40 10.5 7.5 14 1.5

M3.5 6-32 14.0 10.0 12 2.5 M4 — 16.0 11.5 12 2.5

— 8-32 21.0 15.0 12 2.5 M5 10-32 35.0 25.0 10 4.0

— 12-24 49.0 35.0 8 6.0 M6 1/4-20 60.0 45.0 3 10.0 M8 5/16-18 100.0 70.0 2 35

Note: Conductor sized do not represent exact dimensional equivalents

Table 4, Maximum Ampacity of Screw Terminals

3.6.3 Wiring Terminals and Leads

a) All internal wiring shall be routed, harnessed, appropriately laced or in plastic wiring ducts.

b) Conductors and cables shall be run without splices from termination to termination.

EXCEPTION: Splices may be used for repairs. Splices may be used when connecting components that have pig-tail wires permanently attached to the component.

Note: A splice is acceptable if it is mechanically bound and soldered, together with a heat shrink covering or spliced using Crimp On type wire nuts. At NO time are Twist-On wire nuts to be used. Butt splices may be used on circuits under 30 vac or 60 VDC.

c) All internal wiring must be either Listed or Machine Tool Wiring (MTW).

d) All internal wiring must be copper, except thermocouple or special-purpose wire.

e) Insulation must be rated for the highest voltage on any adjacent (bundled) wire.

f) Connectors must be sized correctly for wire.

g) Crimp terminals shall be used with stranded wire only, unless the product is specifically designated for solid wire.

h) Solid wire must be wrapped three-quarters to seven-eighths of a turn around wire binding screws in the direction of the tightening screw.

i) Stranded wire may be wrapped around wire binding screws only if the wire is tinned or soldered, or terminals have cupped washers, upturned edges, or other means of capturing all the strands.

j) Only one wire is to be used per terminal connector (ring, fork, and spade) unless the connector is designed and Listed by an NRTL for more than one wire.

k) Two wires are allowed in pressure connectors if the connectors are designed for two.

l) No more than three terminal lugs shall be attached to a bolt or screw which is not used for equipment ground.

m) If crimped on wire nuts are used, they must be the correct size, with no loose wires and no exposed strands and must be challenged once installed.

n) Approved terminal lugs should be crimped using a ratchet style crimper designed for the specific gauge being crimped.

o) Wire must be stripped using a wire stripper for the specific gauge of wire.

3.6.4 AC Power Connections

a) If ac power conductors are field-wired (conduit, flex conduit), they must terminate in approved pressure terminals.

b) If power supply conductors are in flexible cable or cord, they must either enter the assembly in an approved strain relief fitting or plug into a listed power inlet that is mounted flush with the enclosure.

c) In assemblies that are likely to be accessed by the user, the power supply terminals must be substantially guarded against accidental contact.

d) Shrink tubing is not acceptable as a primary barrier for live parts above 50 V unless listed or recognized for use as an insulation material at the higher voltage.

3.6.5 Polarity

a) Color coding, as shown in Table 5, should be used to indicate terminal and power cord polarity.

NEC Convention Power Line Terminal AC Connector Terminal Pin Power Cord Wire

US European Energized Hot Brass Black Brown Grounded Neutral Silver/Nickel White Blue Grounding Ground Green (round or U-shaped pin) Green Green with stripe

Table 5, Color coding used to indicate polarity

b) All output terminals or devices identified as neutral must be continuous with the input neutral (except for devices with isolated or floating outputs).

c) On items designed for intermittent exposure—for example, lamp holders—the most accessible parts (the shell) must be connected to the neutral.

d) There is no circumstance where only the neutral conductor is switched or fused, leaving a continuous “hot” wire connected to a load.

e) All devices such as receptacles and connectors are to be connected according to the applicable standard (e.g., National Electrical Manufacturers Association [NEMA] standards, NFPA Standards (i.e. NEC) and manufacturer’s recommendations).

3.6.6 Power Circuit Separation

a) Terminal blocks for power circuits shall be grouped separately from control circuits [2].

b) Terminal blocks for power circuits may be located adjacent to control circuits provided that each group is identified by markings, use of different sizes, barriers or by different colors.

c) Internal ac power conductors are to be segregated from other conductors.

3.6.7 Clearance/Creepage Distances

Table 6 summarizes the general clearance and creepage distances in several standards.

For more detailed specifications, see Reference [3]. For voltages greater than 600 V, distances may be determined using engineering calculations.

From To Via

Minimum Spacings, in. (mm) Rating, V

51–

151–

301–

Reference

Uninsulated live part

Uninsulated live part of opposite polarity or different circuit, or grounded part (not enclosure), or exposed metal part.

Through air

1/8 (3.2)

1/4 (6.4)

3/8 (9.6)

UL 508A, Table E

Over surface

1/4 (6.4)

3/8 (9.6)

1/2 (12.7)

UL 508A, Table E

Uninsulated live part

Walls or fittings of metal enclosure

Shortest distance

1/2 (12.7)

1/2 (12.7)

(25.4)

UL 508A, Table E;

NEC 373;

NFPA79; 12.5.2,

NEC Art. 373

Uninsulated live part

Any uninsulated part of the enclosure door

Shortest distance

(25.4)

(25.4)

(25.4)

NEC 373

Edge of any mounted device

Between the device and the enclosure walls

Shortest distance

1/16 (1.6)

1/16 (1.6)

1/16 (1.6)

NEC 373

Table 6, Summary of clearance/creepage distances

3.6.8 High Temperatures

Any assembly subject to internal temperatures exceeding 60 ºC in normal use must have wiring and components rated for the highest possible temperature to which they will be exposed.

3.6.9 Correct Use of Components

a) All components must be used in accordance with the manufacturer’s intent and instructions and in accordance with NRTL specifications and Listing requirements.

b) All components must be rated for the voltage and current range for which they are used.

c) The available fault current is the highest electric current which can exist in a particular electrical system under short-circuit conditions. It is determined by the voltage and impedance of the supply system. Assemblies subject to high fault currents (>10,000 A) must either be rated to withstand the fault or appropriately protected with fast-acting fuses. Approved components must be evaluated within the context of their component category.

3.6.10 Mechanical Bracing of Conductors

a) Conductors used in high-current applications (>100 A) must be supported against movement that can be induced by magnetic forces.

b) Mechanical bracing can be achieved by using locking plastic ties or other means that will not damage the conductors or present a fire hazard.

3.6.11 Overcurrent Protection

a) Fuse holders with fuses intended to be replaceable by an operator must not present a shock hazard during fuse replacement.

b) If line voltage fuses are provided, they must interrupt power to all components in the circuit path except for the power switch.

c) Combination switch/fuse assemblies are acceptable.

d) Internal components must be protected at not more than their input current rating. Internal wiring must be protected as shown in Table 7.

Control-circuit wire size

Maximum protective device rating

AWG mm2 Amperes 22 0.32 3 20 0.52 5 18 0.82 7 16 1.3 10 14 2.1 20 12 3.3 25

Table 7, Wire sizes and associated protective device rating (NFPA 79, Chapter 12).

e) Guidance for motor overcurrent protection can be found in NEC Article 430 [4].

Some general rules are:

(1) Motors generally must be protected to no more than 125% of the full load rating.

(2) Integral thermal protectors are adequate.

(3) Impedance protection is adequate on motors under 1 hp.

3.6.12 Strain Relief

a) There must be no tension on terminals or connectors.

b) Any cable entering an enclosure must be able to be pulled by hand without imposing any stress on the corresponding electrical termination points.

c) Correct fittings should be used and properly installed.

d) The strain relief fitting must be designed for the application.

e) Only one cable is to be used per fitting unless the fitting is specifically designed for multiple cables.

f) On chassis that are cord-connected to an external terminal strip, the cord can be restrained to the chassis by an adequate clamp at a point near the terminal strip.

g) The terminal strip must be substantially guarded against unintentional contact to live parts and labeled to warn of potential voltages (i.e. Danger 480V).

3.6.13 Switches and Controls

a) Switches and controls are defined as those circuit elements that provide operator input to the device being operated. If these elements are switching electrical circuitry, they must be rated for the applied voltage and current.

b) If higher voltages (>50 V dc) are being switched, then the switch must be guarded and appropriately rated.

c) If the switch is being used without reference to the ground potential of the chassis, then it must be rated for the common-mode voltage that is being applied.

Rating example

As an example, assume that the element is a potentiometer that controls a 0-to-5-V signal. If the signal is referenced to chassis ground, then the potentiometer needs to be rated at 5 V and no special precautions are necessary. If on the other hand the same 0-to-5-V signal is floating on a 600 V dc voltage with respect to the chassis ground, then the potentiometer must have a voltage rating for continuous duty at 605 V dc.

d) Electromagnetic loads such as motors, inductors, and transformers have large inrush currents. For the motor industry, control elements are given horsepower ratings. This rating must be used to evaluate the load. The motor’s locked rotor current must be less than the rating of the switch. In general, switches must be rated for both the type and size of the load.

e) If switches and control elements are to be used by an operator, they must not require the use of a tool (screwdriver or wrench) to gain access. All switches or buttons must be located on the perimeter surface of the device and accessible to the operator.

f) A control system must be configured so that the electrical drive is not automatically reapplied to a motor load whenever there is power resumption following a power outage or Emergency Stop button reset.

g) There must be a positive action by an operator to reapply power to a motor.

h) There must be a positive action by an operator to reapply power to a high-voltage power supplies (V >600 V dc)

i) There must be a positive action by an operator to reapply power to interlocked devices. If interlocked, the device must be de-energized when the interlock permissive is removed and must remain in that condition—even if the permissive is re-applied—until positive action by an operator.

j) All Human Interfaces (buttons, switches, lamps and other controls) must be identified with their function and their state. For example, a switch could be labeled “Power” for function and “ON” and “OFF” for state.

k) If the switch is energized by its load circuit, it must be labeled as follows:

l) Switches shall be physically located so that gravity will not cause a switch to close and energize the load.

m) Switches shall be wired in such a manner that the controlled device is energized with the actuation handle in the “UP” position.

n) A knife switch shall be connected so that the blade is connected to the load circuit.

o) Separate power switches and fuses shall be connected so that the fuse is de-energized by the switch to allow the operator to change the fuse safely [6].

3.7 External Wiring

3.7.1 General Requirements

a) Conductors shall be the correct size for the current to be carried. See ampacity tables in section 3.6.1 or refer to NEC Article 310 Conductors for General Wiring, or the UL standard appropriate for the equipment type for guidance [7].

b) The conductor insulation must have the correct rating for the voltage to be applied.

c) Wire insulation must be correct for the application and the environment. Some examples are: tray-rated cable, plenum-rated cable, UV resistant cable for outside applications, oil or chemical resistant cable, temperature-rated cable, or cable rated for direct burial.

d) Cables must be rated for the intended application. See NEC Tables under Article 310 for further guidance [8].

e) Connectors must be properly rated for the voltage and current of the application.

f) Materials must be compatible with the environment: watertight or sealed connectors for outdoor applications, sealed for underwater applications.

g) There shall not be a shock hazard while connectors are not made up.

h) Strain relief must be provided at the connectors to prevent cable damage resulting from use, connecting, or disconnecting [9].

i) Wiring must be located where the potential for damage is minimized.

j) Cables must be protected from damage from sharp corners or edges, from being walked on, from being run over or from exposures to other potential damage that may occur.

k) Cables should be separated from external heat sources [10].

l) Cable shields should be grounded.

m) For EMI shielding purposes, cable shields may be grounded at only one end.

n) Cable shields shall not be used as equipment grounding conductors.

o) Cable shields shall not be used to carry voltages greater than 50 V.

p) Cable trays and wire ways shall be properly installed and grounded [11].

3.7.2 Fill

Conductors installed in raceways, wireways, and wiring ducts shall comply with the following:

a) Raceways - The sum of the cross-sectional areas of all contained conductors shall not exceed 25% of the interior cross-sectional area of the raceway.

EXCEPTION: Raceway fill may increase to 40 % when modifying existing equipment.

b) Wireways - The sum of the cross-sectional areas of all contained conductors shall not exceed 20 % of the interior cross-sectional area of the wireway.

c) Plastic wiring ducts - The sum of the cross-sectional areas of all contained conductors shall not exceed 50 % of the interior cross-sectional area of the wiring duct.

d) Ladder or Ventilated Trough Cable Trays Containing Multiconductor Control and/or Signal Cables Only. Where a ladder or ventilated trough cable tray having a usable inside depth of 150 mm (6 in.) or less contains multiconductor control and/or signal cables only, the sum of the cross-sectional areas of all cables at any cross section shall not exceed 50 percent of the interior cross-sectional area of the cable tray. A depth of 150 mm (6 in.) shall be used to calculate the allowable interior cross-sectional area of any cable tray that has a usable inside depth of more than 150 mm (6 in.).[12]

3.7.3 Cords and Plugs

a) Cords must have the correct voltage and current rating for the application and must be Listed by a recognized NRTL. [7].

b) The outer jacket material must be appropriate for the application (e.g., UV resistant for outdoor applications, oil or chemical resistant, and so forth).

c) Cords shall be provided with strain relief where it enters the equipment [9].

d) Power cords must have a grounding conductor of suitable size for the application.

Note: Two-conductor cords may be used for some applications, such as double-insulated tools and equipment.

e) AC power…