1b Appendix B Electrical Equipment Fabrication.pdf

Engineering Division Electronic Equipment Build Standard Appendix B, Electrical Equipment Fabrication Revision 1

B.1 General

B.1.1 Scope

This specification sets forth the minimum requirements for the fabrication of single voltage source electronic equipment. This specification applies to new equipment fabricated after the current revision date. Users must be aware that older equipment built to previous revisions of this specification may not conform to all current requirements.

B.1.2 Quality

The Laboratory’s intent is to obtain the highest quality of materials and workmanship found in the best custom electronic equipment fabrication. Constructive suggestions for improving quality are welcome and will be given prompt consideration.

B.1.3 Materials

Only new parts of current manufacture shall be used.

Only components listed or recognized by a Nationally Recognized Testing Laboratory

(NRTL) shall be used, e.g., UL, CSA-NRTL, ETL, etc. CE is not an NRTL. Equipment and components marked only with CE must be inspected and approved by the AHJ for research and scientific electronic equipment.

An updated list of NRTL marks can be found at:

http://www.osha.gov/dts/otpca/nrtl/nrtlmrk.html

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

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

Assemblies subject to high fault currents (>10,000 A) must either be rated to withstand the fault or appropriately protected with fast-acting fuses.

Recognized components must be evaluated within the context of their component category.

No substitutions may be made without the approval of the AHJ for research and scientific electronic equipment.

B.1.4 Vendor Information Feedback

All changes agreed to between an external vendor and LBNL shall be marked on one set of documentation, dated, and initialed. The preferred colors are red for deletions and green for corrections and/or additions.

The marked-up set of documents shall be returned to LBNL with the first “equipment” shipment (partial or complete).

B.1.5 Order of Precedence

In case of conflict, the fabrication package documents shall take precedence in the following descending order:

1) Statement of Work

2) Equipment performance specification

3) Schematic circuit diagram

4) Parts list

5) Other drawings in package

6) This and other specifications referenced herein

7) Product data sheets

8) Prototype or sample unit

9) Photographs

B.2 Marking

B.2.1 General

All markings shall be positioned for maximum readability.

Markings shall be legible and neat in appearance and shall display uniformity of style, size, spacing, and alignment of characters. Unless otherwise specified, marking height will be a minimum of 2.54 mm (0.100 inch) and a maximum of 4.0 mm (0.156 inch).

Black ink shall be used on light backgrounds and white ink on dark backgrounds.

Function titles should be marked below a component as shown in Figure B.1.

Figure B.1, Marking locations for function titles

The preferred location of a component reference designation marking (as indicated on the schematic) is above the mounted component for both chassis plates and the outside of rear panels.

See Figure B.2. When a component goes through the chassis plate, the component reference designation should be marked on both sides of the chassis plate. Typically, component reference designations do not appear on the outside of front panels.

Figure B.2, Marking location for component reference designation (rear panel, outside)

For the inside of both front and rear panels, the component reference designation markings above the chassis plate or front panel centerline shall be located above the component. Component reference designation markings below the chassis plate (or printed board assembly, shield, or other item that is mounted perpendicular to the front and rear panels) may be located below the component such that the designation marking may be read right side up when the chassis is upside down. When there is no chassis plate, the front panel centerline may be used as reference for marking orientation. See Figure B.3.

Figure B.3, Marking locations for component reference designations (front and rear panels, inside)

When the component reference designation marking cannot be placed below the component, marking may be adjacent to the component. See Figure B.4.

Figure B.4, Component reference designation marking

Multichannel circuits within the same chassis shall be marked to read left to right from the operating face, as shown in Figure B.5.

Figure B.5, Multichannel circuit marking

B.2.2 Front Panel

Markings on the outside of the front panel shall be silk-screened.

The title of the chassis unit shall be as shown in the title block of the schematic.

The identification number of the chassis unit shall be as follows:

o For Document Control Center numbering, the number will be composed of the drawing number (7 characters) as shown on the assembly, if one exists. Otherwise, the schematic number shall be used. Note: Revision level is omitted.

o For drawings not stored in the Document Control Center system, the number must be a unique identification number matching that of the schematic used to assemble the unit.

The title, drawing number, and serial number (S/N) shall be positioned as follows for a standard 19-in., rack-mounted chassis (see Figure B.6):

1. Top of lettering shall be 2.54 mm (0.1 in.) from top edge of panel.

2. Chassis title is centered on the panel.

3. Drawing number is centered below the chassis title.

4. Serial number is 50.80 mm (2.00 in.) from right edge of panel.

Figure B.6, Positions of markings on the front panel

B.2.3 Chassis Plates and Other Panels

Markings on other than the outside of the front panel may be applied with silk-screen, rubber stamp, or labels, and covered with protective coating if necessary.

Multichannel circuits within the same chassis shall be marked to read from right to left on the outside of the rear panel. See Figure B.5B.

All schematic component reference designations should be marked below the referenced component mounted on a chassis plate. When space is restricted, marking may be adjacent to the component. Component reference designations shall be in accordance with IEEE 200-1975. The marking shall be readable after assembly of components and wiring.

All markings on the top of chassis plates or top covers shall be readable from the front of the chassis.

All markings on the bottom of chassis plates or bottom covers shall be readable from the rear of the chassis.

B.2.4 Component Marking

Circuit breaker current ratings shall be marked on the back of the panel and be visible after chassis assembly (see Figure B.7).

Figure B.7, Location of markings for circuit breaker current ratings

Terminal strips shall have the first and last contacts, and every fifth contact in between, marked on the panel. If the terminal strip is mounted through the chassis, marking shall appear on both sides.

Fanning strips, when used with a terminal strip, shall be marked in the same manner as a terminal strip.

Variable transformer swinger fuses shall be marked with the transformer component number and fuse rating.

All fuses shall have their amperage value and the words “SLO BLO” (if applicable) marked (see Figure B.8).

Figure B.8, Marking for fuses

Chassis with 250 V or more shall have a “CAUTION” or “DANGER” label attached or marked with the appropriate multicolored legend. See Appendix A for more details.

All components mounted through a panel with leads or connections extending through the panel shall have their reference designations marked on both sides of the panel.

All components used for operating and maintaining equipment shall have their descriptive function (e.g., ON, OFF, Start, Stop, Voltage Adj., etc.) marked on the front (operating) side of the panel and the reference designation marked on the opposite side of the panel.

B.3 Assembly

B.3.1 General

Components marked with values and ratings shall be mounted so that they can be easily read.

When it is not possible to mount a small component (such as a diode) to show both the part identification and polarity, the unit shall be mounted so the part identification marking is visible.

Equipment designed for use in areas other than a typical laboratory environment may call for additional fabrication requirements not included in this specification. Example environments include:

public areas, high temperatures, cleanliness, vibration, and corrosive or explosive atmospheres.

Design documentation shall be carefully reviewed to determine if there are any additional fabrication requirements.

Fastening hardware should be of the locking/captive type. Split or internal-tooth lock washers should be used when self-locking screws or nuts are not available.

Bolted or screwed electrical connections shall not depend on any insulating material to maintain contact pressure.

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

When using threaded hardware, there shall be at least one thread visible beyond the front of the nut.

A flat washer shall be placed between the head of the screw and any non-metallic materials and over a slotted hole.

B.3.2 Component Mounting

Components with a mounting key slot, such as switches or potentiometers, shall be positioned with the slot on the bottom.

Chassis receptacles shall be mounted so that the key-way and/or first numbered or lettered terminal will be on the 12 o’clock position.

The ground pin of an ac receptacle should be oriented in the “up” position when mounted.

When heat sinks are specified for components, thermal heat sink compound or silpad should be used unless otherwise specified.

Control knobs and shaft couplings shall have metal inserts and be secured with two Allen-head set screws that are set at 90 degrees to each other.

When mounting an open-backed terminal strip on a metal surface, an insulating sheet 1 mm (0.04 in.) to 2 mm (0.08 in.) thick shall be used between the terminal strip and metal surface.

Semiconductors requiring lead trimming shall be sheared to the required length, not clipped with diagonal-jaw cutting pliers. Lead lengths shall be such that, when the device is fully inserted in the socket, there will be approximately 1 mm of space between the body of the device and its socket (see Figure B.9).

Figure B.9, Appropriate amount of length for semiconductor leads

Knobs shall be positioned on a shaft in accordance with manufacturer’s specifications, or as shown in Figure B.10.

Figure B.10, Knob positioning on shaft

Fuse holders shall have a rubber washer between the fuse holder body and the panel.

Fan Assemblies shall have finger guards installed on the inside and outside of the chassis.

Multi-Deck Switches or potentiometers should have the “A” section of the switch or the lower “R” number closest to the mounting surface, as shown in Figure B.11.

Figure B.11, Proper marking order for Multi-Deck Switches or potentiometers

Component leads shall extend beyond the component body at least 2 mm (0.08 in.) before any bend is made. There shall be at least 4 mm (0.156 in.) length between the component and the soldered connection.

B.4 Wiring

B.4.1 General

Tools used to shape leads shall not damage the leads. The use of round-nosed pliers or automatic lead-forming machines is recommended.

Interconnection leads should be provided with a service loop at the wiring termination unless identified by “D” on line of the schematic, in which case the wiring shall be as short as possible, but not taut.

Figure B.12, Service loops, ties and clamps

Wires shall be arranged to prevent abrasion of the insulation. Long runs of wire shall be secured with ties or clamps.

All wiring connections should be accessible for maintenance.

Transparent tubing or shrink tubing should be used over wiring connections for inspection purposes.

Wiring of circuits greater than 1000 V shall have a minimum air clearance to ground and/or adjacent components of 25 mm (1.00 in.) per 10 kV. The voltage rating of separating insulation may be used to determine a reduced clearance. See Table B.1 for minimum clearance spacing for circuits having 51V to 600V.

From

To

Via

Rating, V Minimum Spacings, in. (mm)

51–150 151–300 301–600 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) 1 (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

1 (25.4) 1 (25.4) 1 (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 1, Summary of clearance/creepage distances

B.4.2 Terminations Through Plastic

Terminations that pass through plastic (Lucite, Bakelite, etc.) are acceptable when two locknuts capture the electrical connection between two washers on either side of the plastic, as seen in Figure B.13. The screw stud that passes through the plastic must be held in place by a washer and a locknut on either side of the plastic. Care must be taken when tightening the stud in place to avoid cracking or plastic cold -flow creepage.

Figure B.13, Terminating Through Plastic

B.4.3 Grounding and Bonding

“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.

Bonding wires must be securely terminated. All grounding and bonding wires shall be attached by dedicated means. The hardware used for grounding or bonding shall not have any other purpose. A grounding conductor that enters the equipment shall be terminated in a pressure wire connector that is clearly marked as a grounding connection. Only one conductor may be terminated in the connector. Solder connections or sheet metal screws shall not be used for grounding or bonding purposes.

All metal not carrying a current must be properly bonded. All exposed metal parts must be positively bonded to one another. 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. Metal surfaces that are securely bolted together are considered bonded if:

o Sufficient area between the surfaces is clean of paint and other coatings to ensure good metal-to-metal contact.

o Bolt heads and nuts/washers are fully in contact with clean, uncoated metal surfaces.

Any enclosure intended for access by the user shall have an internal copper bonding wire installed between the access panel and a bonded surface. A hinge does not constitute bonding unless it is listed by an NRTL or recognized for this purpose. Connections dependant on friction are not acceptable for grounding or bonding.

Where there are removable or hinged portions of a box or chassis with components, a separate bonding wire is required between the removable or hinged portion and the box or chassis to ensure a proper ground. There shall be a ground screw assembly located and labeled with the symbol for earth ground or “EG” on the chassis plate. See Figure B.14. The sole purpose of this assembly is to establish an earth ground. The area on the chassis plate where the ground screw assembly is installed shall be clean of paint, anodizing, and other coatings to ensure metal-to-metal contact.

Apply a light coat of an oxide inhibitor, such as Penetrox, in the corrosion area before installing ground screw hardware.

Figure B.14, Ground Screw Assembly Options (Minimum hardware size is #10)

For tightening torque required for connecting hardware, i.e., ground screw assembly, see Table B.2.

Screw or bolt size Tightening torque

Metric (SAE) N×m (lbf×ft)

M6

M10

M12

(No. 8 or smaller)

(No. 10)

(1/4 in.)

(5/16 in.)

(3/8 in.)

(7/16 in.)

(1/2 in.)

(9/16, 5/8 in. or larger)

(1.5)

(2.0)

(6)

(11)

(19)

(30)

(40)

(55)

Table B.2, Tightening torque for connecting hardware

B.4.4 Wire Termination

Terminal connectors (lugs) shall be closed-ring and have the proper stud size and wire gauge. The barrel of the lug shall be filled with solder or crimped.

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

Only one wire is to be used per terminal connector unless the connector is designed for more than one wire.

No more than three terminal lugs shall be attached to a bolt or screw.

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

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

Wires shall not be spliced. The insulation on a wire shall be continuous between terminations.

Unused component wire leads, such as a transformer center tap, shall be terminated at tie points.

A tie point shall be used for the junction of two or more wires and/or the termination of single component leads.

Unused terminals on any component shall not be used as tie points.

When solid wire is specified, the wire may be terminated with a lug or soldered to a terminal.

A sound mechanical connection of all wires to a terminal point should be made before applying solder.

Thermocouple wire that terminates at a screw may be terminated by looping wire around the screw three-quarters to seven-eighths of a turn in a direction that will tighten the loop when the screw is tightened.

B.4.5 Wire Routing

Grommets shall be used to protect wires passing through metal surfaces.

Wires within a wire harness should be parallel with a minimum of crossover. The harness shall be routed to eliminate interference with components, contact with heat-dissipating items, or abrasion on sharp or rough edges. Special consideration should be given to routing wire harnesses within a chassis that contains a combination of digital signal, relay control power, ac voltage, and high voltage.

Tie-wraps or nylon lacing shall be used for bundling wires. Ties at breakouts should be made as close as possible to each side of the breakout and as close to each side of the bend without placing the tie in the bend itself. Sufficient tie-down clamps must be used to secure all wiring harnesses to chassis.

Terminal blocks for power circuits shall be grouped separately from control circuits. Internal ac power conductors are to be segregated from other conductors.

B.4.6 Wire Types and Sizes

All internal wiring must be either Listed or Machine Tool Wiring (MTW). All internal wiring must be copper, except thermocouple or special-purpose wire. Insulation must be rated for the highest voltage on any adjacent (bundled) wire.

Hook-up wire shall be per MIL-DTL-16878G, Types M16878/2, /18, or M16878/3, /19 for vinyl and NEMA HP 3 for Teflon. Wire-wrap wire shall be Kynar (polyvinylidene fluoride) insulated. All chassis hook-up wire shall be sized as indicated in Table B.3. The preferred chassis wiring size and type is 18 AWG Teflon or larger.

Maximum Current (A) AWG Vinyl AWG Teflon

3 22 24 4 20 22 5 18 20 7 16 18 10 14 16 15 12 – 20 10 – 30 8 –

Table B.3, Sizes of chassis hook-up wire

B.4.7 Color Code

MIL-STD-104 style color values may be used to color code the function of wires.

Chassis hook-up wire may be coded as shown in Table B.4.

Color Function

Green Grounds, grounded elements, ac ground Brown Heaters or filaments Red Primary power supply, B+

Orange Screen grids clock Yellow Cathodes and transistor emitters, high logic Black Control grids and transistor bases, ac “hot” Blue Anodes (plates) and transistor collectors, control Violet Primary power supply—minus voltage White ac neutral

Table B.4, Chassis hook-up wire color codes by function

Chassis wiring for dc power may be coded as shown in Table B.5.

Wire Color Voltage (V)

Red +151 to +500 White/Red +61 to +150 White/Brown/Red +26 to +60 White/Red/Orange +7 to +25 White/Red/Yellow +2 to +6 Violet –26 to –60 White/Violet –11 to –25 White/Violet/Yellow –2 to –10 Green Ground

Table B.5, DC power coding for chassis

Color-coding, as listed in Table 11.3-6, shall be used for ac power wiring.

Service Phase A Phase B Phase C Neutral Ground

115V 60 Hz 1f Black — — White Green 208V 60 Hz 3f “Y” Black Red Orange or Blue White Green 230V 60 Hz 3f delta Black Red Orange or Blue — Green 115V 400 Hz 3f delta Black Red Orange or Blue — Green 208V 400 Hz 3f “Y” Black Red Orange or Blue White Green 480V 3f Brown Yellow Violet White Green

Table 6, Color coding for ac power wiring (100 V and greater) for single and three phase systems

Color-coding, as listed in Table 11.3-7, shall 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 B.7, Color-coding used to indicate polarity

B.4.8 Miscellaneous

AC wiring shall be twisted unless otherwise specified. Preferably, ac wiring will be routed on the underside of the chassis plate and/or routed separately from other wires.

Potentiometers and variable resistors shall be wired so that “CW” or an arrow designates clockwise rotation as viewed from the shaft end.

Any voltage-dropping resistance used with an indicating light shall be connected between the light and the “hot” or primary voltage source (see Figure B.15).

Figure B.15, Typical resistor connection to indicating light

For ac power input circuit configurations, it is recommended that the line fuse be installed adjacent, and as close as practical, to the input power switch which is wired to the power entry point using minimal internal chassis wiring (see Figure B.16).

The power switch—line fuse—load combination would provide additional electrical shock protection to the individual checking and/or replacing the line fuse while the equipment is connected to a live branch circuit. In this configuration, the internal wiring—between the branch circuit line power entry point through the switch to the line side of the fuse terminal—will rely on the branch circuit over-current device for ground fault protection. The impedance of the internal chassis wiring and current rating of the power switch is critical for providing sufficient fault current to trip the branch circuit over-current device without causing damage to these components subjected to the branch circuit fault current potential.

When using the branch circuit input power configuration, the power cord and internal chassis wiring shall be no less than 16 AWG and the internal chassis wiring shall be no more than 36 in. in length.

The chassis power switch shall be rated to perform under the anticipated branch circuit fault current conditions.

Figure B.16, Preferred branch circuit input power circuit configuration

The incoming or “line-side” ac wiring shall be connected to components as follows:

Components Connection Switch, single-throw, terminals on each end Top terminal Switch, double-throw (used as single-throw) Swinger

Figure B.17, Single throw and double throw switches

For the alternate branch circuit input power configuration shown in Figure B.18, line fuse—power switch—load combination, it is recommended the line fuse be installed adjacent, and as close as practical, to the input power entry point using minimal internal chassis wiring.

The line fuse—power switch—load combination would provide electrical circuit and fire hazard protection for the line-to-ground-fault condition. In this configuration, there will be minimal internal chassis wiring between the line-power entry point and the line-side fuse terminal. This minimizes reliance on the impedance and rating of the internal chassis line-side wiring and components for line-to-ground-fault protection. With this configuration, the internal chassis fuse rating will be the primary protection device for line-to-ground-fault conditions.

Figure B.18, Alternate branch circuit input power circuit configuration

All exposed ac voltage wiring shall be covered for safety in an appropriate manner, such as with a nonconductive material like Lucite or shrink tubing that is NRTL listed for this purpose.

It shall be verified that the chassis is free of sharp burrs, metal shavings, wire clippings, solder splatter, and other foreign material that could cause electrical shorts.

B.4.9 Busbars

A busbar is a strip or bar of copper, brass or aluminium that conducts electricity within a switchboard, distribution board, substation, battery bank, or other electrical apparatus. Its main purpose is to conduct a substantial current of electricity. Busbars must not function as a structural member.

A busbar must be sufficiently rigid to support its own weight, as well as forces imposed by mechanical vibration and possibly earthquakes, as well as accumulated precipitation in outdoor exposures. In addition, thermal expansion from temperature changes induced by ohmic heating and ambient temperature variations, and magnetic forces induced by large currents must be considered.

Busbars may be connected to each other and to electrical apparatus by bolted, clamped, or welded connections.

Figure B.19 shows the cross sectional ampacity of copper bar. The ampacity of copper bar may be determined by multiplying the cross sectional height and width of the bar times 1000 A/in2.

Figure B.19, Cross sectional ampacity of copper bus bar

B.4.10 Quality Assurance

All equipment must be inspected through the EESP equipment inspection program (PUB 3000, Chapter 14)

Manufacturers shall perform all specified tests and inspection requirements, and shall verify that the materials, dimensions, markings, and workmanship meet requirements.

Manufacturers’ test equipment, inspection methods, and test data shall be acceptable to LBNL. A certificate of conformance shall accompany each shipment of product when specified.

B.5 Applicable Specifications

The latest revisions of the following documents form a part of this specification, to the extent stated herein:

Specification Number Title

ANSI/J-STD-001 Requirements for Soldered Electrical and Electronic Assemblies ASME Y14.5M 1994 Dimensioning & Tolerancing

IEEE 200-1975/ANSI Y32.16-

Standard Reference Designations for Electrical and Electronics Parts and Equipment

IEEE 315-1975/ANSI Y32.2-

Graphic Symbols for Electrical and Electronics Diagrams

MIL-A-8625 Anodic Coatings for Aluminum and Aluminum Alloys (Anodizing) MIL-C-5541 Chemical Conversion Coatings on Aluminum and Aluminum Alloys MIL-STD-104 Limits for Electrical Insulation Color MIL-STD-681 Identification, Coding, and Application of Hook-Up and Lead Wire MIL-DTL-16878 Wire, Electrical, Insulated, General Specification for UL 486A-486B Wire Connectors UL 508A Industrial Control Panels UL 508 Industrial Control Equipment

B.6 Revision Log Date, Revision # Brief Description of Revision / Changes Sec. #, Parag.

9/8/2014 Revision 1

Initial version All

DOCUMENT INFORMATION

Title: Requirements Management Document number Revision number 1 Publication date: 9/8/2014 Effective date: 9/9/2014 Next review date: 7/1/2015 Last Edited By: pbong@lbl.gov

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