Instrument and Electrical Control Panels and Equipment

Table of Contents

Purpose

Scope

2. Instrument and Electrical Control Panels and Equipment

2.1 This article applies to all instrument and electrical control enclosures 220V / 120 VAC and below located and used in plants and equipment. For sale of equipment, the instrument/electrical designer shall verify these requirements with the customer’s representatives before proceeding with facility or equipment design.

2.2 This standard is intended for use International Level.

2.3 Contract drawings shall supersede any paragraph in this standard.

2.4 Pressure in a control panel application shall be limited to 150 psig.

2.5 If there are potential retrofit implications, paragraphs are designated by an (M) are Mandatory for all applications, both new designs and existing facilities. Exceptions to mandatory items require a FAR analysis and approval by Process Safety Engineering. Paragraphs that are marked with an (R) are Recommended and will generally be included on new facilities and should be reviewed by Operations/OPHR teams for possible application to existing operating facilities.

3. RELATED DOCUMENTS

3.1 Engineering Articles

Copper Tubing, Brass Fittings, and Valves for Instrument Service Copper Tubing, Brass Fittings, and Valves for Instrument Service.

Painting and Corrosion Protection of New Construction for Design Temperatures to 649°C (1200°F)

Standard Clean (Class SC) Inspection and Acceptance Requirements

Process Clean (Class B) Inspection and Acceptance Requirements

Oxygen Clean (Class AA) Inspection and Acceptance Requirements

Fluorine Clean (Class AAAA) Inspection and Acceptance Requirements

Electronic-Grade Stainless Steel Piping Systems

Standard Nameplates; Blank Sizes and Engraving Details

Standard Wire and Cable Types

3.2 EH&S Article

Selection of Cleaning Agents and Methods for Equipment Used in Oxygen Service

3.3 National Fire Protection Association (NFPA)

NFPA 70 National Electric Code (NEC)

3.4 Underwriters Laboratories Inc.

UL 489 Safety Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit-Breaker Enclosures.

UL 1077 Supplementary Protectors for Use in Electrical Equipment.

3.5 American National Standard Institute (ANSI)/NEMA

ANSI Z535.4 Product Safety Signs and Labels.

4. Manufactured Enclosures

4.1 Prefabricated enclosures shall always be the first consideration as outlined in paragraph 4.3. Custom-fabricated enclosures shall be used only when standard prefabricated sizes are not available to accommodate design requirements.

4.2 Enclosures shall be selected for the proper environment based on the following:

Rating	Description	Application
Type 1	Indoor use to provide protection from contact with enclosed equipment and from falling dirt.	Office, Control Rooms, Lab Equipment
Type 2	Indoor use to provide protection from contact with enclosed equipment and from a limited amounts of falling water and dirt.
Type 3	Outdoor use to provide a degree of protection from windblown dust and rain; undamaged by the formation of ice on the enclosure.
Type 3R	Outdoor use to provide a degree of protection from falling rain; undamaged by the formation of ice on the enclosure.
Type 4	Indoor or outdoor use to provide protection against windblown dust, falling rain, splashing water, hose-directed water, and undamaged by the formation of ice on the enclosure.	Noncorrosive process plants, Sumps, Steam out pits
Type 4X	Indoor or outdoor use to provide protection against corrosion, windblown dust, falling rain, splashing water, hose-directed water, and undamaged by the formation of ice on the enclosure.	Corrosive process plants, Sumps, Steam out pits
Type 6	Indoor or outdoor use to provide protection from occasional submersion to a limit depth; undamaged by the formation of ice on the enclosure.
Type 12	Indoor use to provide protection against dust, dirt, dripping water, flying fibers, dripping noncorrosive liquids, and external condensation.	Noncorrosive process plants
Type 13	Indoor use to provide protection against dust, spraying of water, oil, and noncorrosive liquids.	Machine shops

4.3 Generally Rittal, Hoffman, Hammond type or equal manufactured standard enclosures shall be used for petrochemical or other projects. When specified sizes are not available or delivery issues are encountered, alternates shall be approved.

4.4 All enclosures are preferred to be of a straight face design, having no cantilevered shelves or work area, and a maximum height of 2300 mm (90 in) including floor stands. Enclosure width and depth will vary with the amount and size of instruments and control devices.

4.5 All control enclosures shall have hinged doors.

4.6 All internal equipment (for example, relays, timers, or terminal blocks) shall be installed on mounting panels internal to the enclosure. Mounting panels can be installed on the side and on the inside of the door of metal enclosures only. Preferred mounting method of side and door panels is stud welding. Self-clinching studs are acceptable if the panel will be painted after installing the studs. Side walls and doors are acceptable mounting surfaces for external equipment.

4.7 All fully assembled instrument and electrical control enclosures over 70 lbs in weight shall be equipped with lifting lugs.

4.8 All enclosures containing safety/interlock circuits will be equipped with pad lockable hasps.

5. Modular Enclosure

5.1 Modular enclosures shall be designed for the environment in which the enclosure shall be located.

5.2 All modular enclosures shall be specified by manufacturer (for example, Rittal or Hoffman type or equal).

5.3 All enclosures are preferred to be of a straight face design except for a keyboard shelf and a maximum height of 2290 mm (90 in) including plinth, cable base, mobile base, or mounting feet. The width of a modular panel may vary with the amount and size of instruments and control devices.

5.4 A maximum length of 2540 mm (100 in) can be connected together for safe transportation. If width is more than 2540 mm (100 in), check with Corporate Transportation and installation site as to acceptability of dimensions and weights. Check with enclosure manufacturer if enclosure stiffeners are needed.

5.5 All modular enclosures shall have front and/or rear access with three-point latched hinged doors.

5.6 Modular enclosure side walls, tops, doors, and bottoms, are supplied with earthing lugs and shall be effectively bonded together to the frame. Various components on modular enclosures are supplied with foam gasketing and attached to the frame via nylon nuts for the mounting bolts. This attachment method can create metallic parts, which are unearthed if not properly bonded to the frame. It is recommended that the earthing straps be purchased from the manufacturer supplying the enclosure.

6. FABRICATED PANEL

6.1 Carbon and Stainless Steel

6.1.1 The panel shall be fabricated from 14-gauge, 2.667 mm (0.075 in) cold-rolled steel plate minimum thickness, uncoated. Interior angle framing, if required, shall be 1/8 in minimum thickness. Other than the front on the enclosure, each side top, bottom, and rear shall be constructed of a continuous sheet. The unit shall be assembled using all welded construction. All top and side exterior seams shall be continuous welds and shall be ground smooth. The fabricator is responsible for selection of materials, framing, and bracing as required to produce a structurally sound rigid unit that may be lifted, shipped, and installed without any resulting frame distortion.

6.1.2 All exterior panel doors shall be fabricated from a minimum of 12-gauge cold-rolled steel plate with internal stiffeners included, as required. The design shall be such that doors are flush with the panel surface unless otherwise detailed on the panel drawings. The door recesses shall be fully gasketed to provide a weathertight enclosure. The edges of the doors shall be formed to provide adequate gasket bearing surface. Fixed door posts shall be provided between multiple rear of panel access doors if required on the panel drawings. Each door shall be equipped with full-length stainless steel continuous hinges and a three-point latching unit. A locking device will be installed when specified on contract drawings.

6.1.3 Each panel over 70 lbs in weight shall be equipped with lifting lugs if possible. Lifting lugs shall penetrate the interior mounting angles. If panels are unable to accept lugs due to equipment such as ducts, provisions should be made for a fork truck. The lifting lug holes shall be used to attach the roof or canopy if required. If the lifting lugs are permanent, they should be welded or screwed and gasketed.

6.1.4 The panel supplier shall provide additional case support brackets, as required, for all face of panel instruments. Support brackets will not interfere with maintenance or removal of instruments and will be free of sharp edges.

6.1.5 The panel supplier shall install a 10 in x 12 in print pocket on inside of right rear door per panel drawings, if required.

6.1.6 The panel supplier shall provide items such as mounting brackets and plates, to mount all rear of panel instruments. Brackets shall be constructed to provide easy access and removal of instrumentation. Welding utility boxes (used for receptacles and light switches) to the panel structure will not be permitted.

6.1.7 Internal mounting plates shall be a minimum of 12-gauge steel. Plates shall be secured to internal surfaces by welded mounting channel or stud welding. No holes shall be drilled through exterior panels for fastening mounting plates.

6.2 Aluminum

6.2.1 The panel shall be fabricated from type 5052 for bending. Minimum thickness shall be 0.090 in, uncoated. Other than the front on the enclosure, each side top, bottom, and rear shall be constructed of a continuous sheet. The unit shall be assembled using all welded construction. All top and side exterior seams shall be continuous welds and shall be ground smooth.

6.2.2 All exterior panel doors shall be fabricated from type 5052 for bending minimum thickness of 0.090 in, uncoated. The design shall be such that doors are flush with the panel surface unless otherwise detailed on the panel drawings. The door recesses shall be fully gasketed to provide a weathertight enclosure. The edges of the doors shall be formed to provide adequate gasket bearing surface. Continuous hinges are preferred on doors with a latching device.

6.2.3 Self clinching studs shall be used to for mounting plates, DIN rails, or channels. Welding of studs for mounting plates or channels is not permitted.

7. Face of Plant Layout

7.1 All face of panel instruments shall be located for ease of operation. Any instrument (for example, controllers, recorders, and indicators) that requires constant operation/observation shall be installed at a maximum elevation of 1680 mm (66 in) and minimum elevation of 915 mm (36 in).

7.2 When an annunciator unit is installed on the face of the enclosure, it may be located above the maximum elevation of 66 inches, because constant operation is not required. If the annunciator is located above 66 inches, the acknowledge, reset, and test pushbuttons for the annunciator shall be located below the 66 inches.

7.3 Location of instruments on the face of the enclosure should consider the location of the required AC and DC wiring for the instruments on the internal side of the face of the enclosure such that segregation of AC and DC wiring is maintained. AC and DC shall only cross each other at 90 degrees when necessary. Device spacing should consider the requirements for wiring and maintaining such devices. Related devices shall be grouped together and each device shall be functionally identified using a descriptive nameplate. See Section 24 for nameplate.

8. AC Power Distribution

8.1 The designer shall confirm the required type of voltages and frequencies (for example, regulated, non regulated, UPS, or other) before starting any panel work. This information will be obtained from the Process Control or Electrical Engineer. Interrupting rating of disconnect may also need to be verified.

8.2 A disconnecting means shall be provided for each incoming supply circuit, and the disconnecting means shall open each unearthed conductor. When two or more disconnects are provided for multiple supply circuits, they shall be grouped in one location of the enclosure. The feeders shall be sourced from a circuit breaker panelboard, which will provide for both wire protection and circuit isolation. If multiple circuits are fed from the same panel board, they must be from the same phase bus to limit the voltage between phases.

8.3 When the enclosure is supplied with power, a “caution” nameplate shall be located on the enclosure access. Nameplate shall be yellow (106) background with black lettering according to ANSI Z535.4 and contain the highest voltage level in the panel. If known, panel and breakers supplying power should be added. This label is not needed for sale of equipment if the customer will be supplying their own label at time of installation.

8.3.1 When the enclosure is supplied by more than one source, such that more than one disconnect switch is required to disconnect all power within the enclosure, the wording “More than one disconnect is required to de-energize this enclosure” shall be inserted and the additional circuits added. Nameplate shall be yellow (106) background with black lettering according to ANSI Z535.4 and contain the highest voltage level in the panel. If known, panel and breakers supplying power should be added. This label is not needed for sale of equipment if the customer will be supplying their own label at time of installation.

8.3.2 According to section 110.16 of the NEC, if the enclosure requires periodic examination, adjustment, servicing, or maintenance while energized, it shall be marked to warn qualified persons of potential electric or arc flash hazards. The marking shall be located on all accesses to the enclosure that would typically be used to perform energized work. The nameplate shall be Orange (161) background with black lettering according to ANSI Z535.4 and say:

8.4 Supplementary protectors, circuit breakers type UL 1077, are permitted to be used as the main disconnect/over current protection for the enclosure as long as it is fed from a source that is protected via a listed type UL 489 primary protection device. It is not permitted to feed a sub-enclosure from the main enclosure via a supplementary protector unless the sub-enclosure has a type UL 489 protector as its main disconnect/over current protection.

8.5 One circuit breaker can protect several devices; however, devices may need to be protected individually for maintenance. For higher reliability, redundant power shall be confirmed by the designer. Common mode failure and reliability of the plant design must be accounted for.

8.6 For protection of individual circuits or instruments in the enclosure, circuit breakers are preferred. If the appropriate trip characteristic or size cannot be obtained via the circuit breaker, use fusible switch blocks with the appropriate fuse size and characteristic (very fast-acting, fast-acting, slow blow).

8.7 All disconnect switches/circuit breakers shall indicate whether they are in the “off” or “on” position and if mounted vertically shall have the up position as “on”.

8.8 All disconnect switches must be labeled, either on the device or back panel, to match the assigned label from the enclosure drawing.

8.9 When an instrument is furnished with a power cord, a dedicated receptacle shall be mounted close to the instrument. A nameplate shall be installed as close to it as practical and shall denote the ampere rating of the over current protective device and the intended use for the receptacle. In no case shall the plug be cut from the cord and hard wired to terminal blocks. Cutting the cord will negate the UL listing of the device.

8.10 When appropriate, a GFCI receptacle can be installed in the enclosure for maintenance use, as long as the power source is properly protected and will not cause a current overload, which would lead to tripping of the enclosure main circuit protection. A nameplate shall be installed as close to it as practical and shall denote the ampere rating of the over current protective device if the overcurrent device is less than 15A.

8.11 Devices requiring 220 / 120 VAC power usually require an earthing conductor. This earth wire will be green or green with a yellow stripe and run directly to enclosure’s ac earth bus. When multi-devices are used, “jumpering” of the earth wire is not permitted.

9. DC POWER DISTRIBUTION

9.1 All 24 Vdc power shall be generated with a power supply. For ease of installation, DIN rail mountable is preferred. Linear or switching power supplies are acceptable as long as ripple is less than 100 mV peak to peak. Switching power supplies are generally much smaller and are preferred for smaller panels. If there are multiple power supplies, it is preferred that analog devices are powered from one supply and discrete devices are powered from another. Discrete power supplies can be regulated or unregulated. Power supplies shall be rated for the temperature and area classification of the enclosure. The common/0 Volt output terminal of the power supply shall be tied to chassis earth unless specific equipment requires floating DC power.

9.2 For a higher reliability installation, such as a Programmable Electronic System (PES) enclosure, a power supply with built-in redundancy or multiple supplies with an automatic switching unit shall be used. Redundant connected power supplies shall have DC “OK” indication as well as contacts for remote DC “OK” indication back to the PES. Redundant power supplies shall be fused separately and may need disconnecting terminals on the outputs if the power supplies are required to be replaced with the plant energized. Separate the power source to the power supplies if necessary. Other equipment such as ambient analyzers and emergency indication lights may also need redundant power and should be confirmed with the process controls engineer.

9.3 The designer shall size or confirm the power supply size by determining the total amount of amps required in the panel. This information should be determined jointly between design and the process control engineer. Sizing should consider inrush and future additions.

9.4 For multiple 24 Vdc users, the (+) and (-) distribution shall be through terminal blocks on a common terminal strip. Separate blocks may need to be supplied to meet reliability goals of the design. Fusible switch blocks with LED blown fuse indicator with appropriate fuse size and characteristic (very fast-acting, fast-acting, slow blow) are preferred to be used for all (+) wiring. For high reliability installations, a fuse shall be installed for each device. Fuses should be checked by someone knowledgeable in circuit protection. Circuit breakers are permitted but will cause a voltage line loss that may not be acceptable to instruments being fed with the circuit breaker.

9.5 All fusible switches must be labeled, either on the device or back panel, to match the assigned label from the enclosure drawing and control schematics.

9.6 All fusible switches if mounted vertically shall have the up position as “on”.

10. Earthing

In this paragraph, we will discuss about earthing techniques and requirements for instrument and electrical panels.

10.1 All AC earthing shall terminate at an earth lug, earthed terminal block, or earth bus bar which is mechanically attached to the DIN rail. The bolting of the DIN rail to the enclosure back panel shall be considered the earthing path to the main enclosure earthing lug. When such mechanical connection of the DIN rail cannot be ensured, it will be required to run a properly sized earth jumper from a earthed terminal block to the main enclosure earth lug or earth bus bar.

10.2 DC wiring shields shall be terminated to isolated terminal strips and then “jumped” together with the final terminal having a earth wire tied to the main enclosure earth lug. Acceptable methods of “jumpering” are to use terminal blocks with center connectors or insertion bridges, earth terminal blocks on DIN rail, or bus bar with correct connection terminal. The DIN rail or bus bar must be isolated from the panel using insulated supports. This is incorporated to ease in the troubleshooting of earth loops in the wiring circuits. If the single wire to earth is removed and an ohm reading is taken between it and earth, an infinite reading on the meter will indicate no earth loops exist.

10.3 At connections where the shield is not terminated, the shield and drain wire shall be cut back and insulated so that the wire cannot come in contact with any item.

10.4 Shields that pass through enclosures shall not terminate but be landed on terminals with no disconnects. All landed shield drain wires shall be insulated with clear heat shrink tubing for their entire exposed length to prevent accidental contact with any item.

10.5 Enclosures supplied with removable metal non-current-carrying parts that are to serve as earthing conductors shall be effectively bonded to ensure electrical continuity, and the capacity to conduct fault currents likely to be imposed on them, according to the NEC section on Grounding and Bonding.

10.6 The ground wire shall be sized per the NEC. However, minimum earth wire size to be used is 18 AWG.

10.7 Earth bonding wire size for Enclosure shall be a minimum size of 12 AWG.

11. Electrical Control Devices

11.1 All control devices shall be rated for the voltage, amperage, and area classification of use.

11.2 All control devices shall be installed per manufacturer’s instructions.

11.3 How to select Relay?

Relay selection shall be based on the coil voltage and frequency (24 V or 220/120 V) and the number of contacts required (2-12). This information can be obtained from the wiring schematics. One spare contact is recommended on all relays specified for possible future use. All 220/120 VAC relays controlled by a PES or programmable device shall have a surge suppressor across the coil. All 24 Vdc relays controlled by a PES or programmable device shall have a Motorola model 1N4005 diode, or equal, across the coil. It is recommended that relays have an indicator. Indicator may be mechanical or a light. If necessary, relays can be specified with manual overrides for maintenance and checkout purposes.

12. Terminal Block and Related Hardware

12.1 Terminal blocks shall be of screw clamp design and be UL recognized, CSA listed, or FM approved. Screw terminal strips are acceptable if the wires have upturned or locking forks added.

12.2 Terminal blocks shall be rated for the voltage, amperage, and gauge of wire being used.

12.3 All terminal blocks shall be numbered consecutively. AC and DC terminal strips shall be segregated within the panel.

12.4 All terminal blocks to be labeled on all levels and both sides, if possible. Terminals assembled at a panel shop shall have the labels typed or pre-printed. If labeled in the field, permanent ink can be used to label the terminals if preprinted labels are unavailable.

12.5 It is recommended that control panels be designed for a minimum of 20 percent spare terminals for future expansion.

12.6 No more than two wires per screw clamp connection. The maximum size of the two wires should be determined by the listed rating of the terminal block.

12.7 Terminal blocks with wiring to the field, shall be divided into the internal side and field side. Internal wiring should not be connected to the field side of the terminal block. Permanent jumpers on the terminals shall be on the panel side of the terminals.

12.8 When jumper bridges are used, they shall be the screw type when terminal block selection provides provisions for screw type jumpers; such as Allen Bradley type 1492-J3 terminals. Plug in jumpers shall be provided on terminals without provisions for screw type jumpers; such as Phoenix Contact Type UT terminals. Plug-in jumpers shall be secure and not readily removable; such as Phoenix Contact type FBS bridges. Partition plates may be required to prevent adjacent bridges from shorting to each other.

13. WIRING

13.1 Wire types and sizes, unless otherwise indicated on contract drawing, shall be as detailed in Standard Wire and Cable Types | Electrical and Instrumentation.

13.2 Internal wiring of components shall be according to the contract drawing and this paragraph. The minimum size of wiring inside the enclosure shall be 18 AWG for a single conductor. The minimum wire size for I/O shall be 26 AWG as part of a cable assembly or 28 AWG if ribbon cable is used. Paired wires shall not be less than 20 AWG. Wire shall always be sized for the load per the NEC. All wiring shall match over current protection.

13.3 The installed wiring shall be stranded soft-annealed copper with a thermoplastic insulation rated for 90°F, rated for 600 VAC, and a NEC type MTW, THHN, or THW rating. Multi-twisted pair cable used for field I/O connections will be a type PLTC rated for 300 VAC minimum. Wiring insulation must meet highest voltage present in the enclosure or raceway.

13.4 Per the NEC AC power and control and DC signal circuits shall be separated. If AC and DC signal circuits need to cross, they will only cross perpendicular to each other, and these crosses will be kept to a minimum and separated by at least 2″.

13.5 Analog signals to a PES, or programmable device shall use shielded cable as much as possible. Discrete signals shall be unshielded cable or individual conductors.

13.6 Intrinsically safe circuits shall be separated from conductors of any non intrinsically safe circuit per the NEC. Intrinsically safe wiring shall be secured to prevent it from coming in contact with other wiring or energized parts. Wiring shall be identified per the NEC section on Intrinsically Safe Systems.

13.7 RTD and thermocouple wire shall not be run or bundled with any AC wire. Thermocouple extension wiring shall be as per Standard Wire and Cable Types | Electrical and Instrumentation and of the appropriate type to match the thermocouple. RTDs shall be a shielded triad as per Standard Wire and Cable Types | Electrical and Instrumentation.

13.8 Wires terminating on terminals shall have the appropriate sized ferrule, or the wire strands shall be tightly hand‑twisted before insertion into the terminal screw connector. If ferrules are used, the ferrule manufacturer’s crimping tool must be used. Terminal screw connectors shall be torqued to the terminal manufacturer’s requirements using a calibrated torquing screwdriver.

13.9 Wires terminating on equipment with screw terminals shall have either insulated forks with upturned ends, spring spades, insulated ring terminals, or insulated spade connectors. Forks and ring terminals shall be sized for the wire and connection screw size. Spade terminals shall be sized for the wire and spade size.

13.10 Conductors entering enclosures shall be protected from abrasion.

13.11 Openings through which conductors enter shall be adequately closed after installation.

13.12 Individual conductors crossing a hinged door or panel shall be bundled together and protected by appropriately sized wire loom. AC and DC conductors shall be bundled separately. Multi-pair cable crossing a hinged door or panel shall be secured to prevent pinching in the hinge.

13.13 All wires to be labeled per the contract drawings. Labels can be pre-printed or heat transfer. All labels utilizing water soluble ink shall have clear heat shrink tubing or a clear covering on the label. Both ends of the wire to be labeled per the contract drawings.

13.14 Wires shall not be spliced between terminal points in the panel. If splicing is necessary such as in a retrofit, refer to this article Electrical Work Technical Specification Petrochemical Plants section (Splices in Wiring).

14. Wire Color Codes

14.1 The following wire color code shall be followed.

Black – Line voltage AC

White – Neutral grounded conductor

Green – Earthed conductor

Red – Controlled or switched AC

14.2 The following wire color code is recommended only. Plant standards, group standards, and pre-manufactured equipment most likely will differ slightly from those listed.

Yellow – Control or power from another source (wiring that remains energized when the individual panel disconnect is in the off position)

Blue – Intrinsically safe

Orange – DC power or controlled DC

Gray – Grounded DC conductor or ungrounded DC common conductor

14.2.1 Other colors normally available from most manufacturers for 10 AWG or less are brown, purple (violet), or pink.

14.3 Analog wire colors, unless noted otherwise on contract drawings, shall be as follows:

Wire Usage Color

Thermocouple Type “J” (+) White (-) Red

Thermocouple Type “K” (+) Yellow (-) Red

Thermocouple Type “T” (+) Blue (-) Red

RTDS Red (White)(Black) | White (Red)(Yellow) | Black (Red)(Yellow)

mV & mA (Instrument Signal) (+) Black (-) White or Clear

Bentley Nevada (-)18 Vdc Red

Proximeters Common Black Signal White or Clear

Note: Normally specify 3-wire RTDs. Typical lead wire color will vary depending on manufacturer. In all cases 3-wire RTDs will have two wires of the same color. Substitute manufacturer’s color coding in the chart above.

15. Enclosure Equipment Installation and Spacing

15.1 A minimum of 25 mm (1 in) clearance must be maintained from the door to any live metal part. As per NEC section on Cabinets, Cutouts Boxers, and Meter Socket Enclosures.

15.2 A minimum of 25 mm (1 in) clearance must be maintained from the back of all door-mounted instruments, including wired connections, from back-mounted panel devices, enclosure walls, or structures when the door is closed. There shall be an airspace of 12.7 mm (1/2 in) between the walls, back, or metal gutter to any exposed energized part of a device mounted in the enclosure.

15.3 AC and DC equipment shall be segregated by distance or via separate mounting panels.

16. Terminal Block and Wire Duct Spacing

16.1 Without Wire Duct

16.1.1 All wiring not in wireways shall be neatly bundled with nylon ties and routed using cable ties secured to the internal structure of the enclosure with epoxy resin or with screws. Adhesive-backed cable tie mounts are not allowed.

16.1.2 The following are minimum recommended distances for wiring connections without wire duct:

- - 2.5 in between the connection and side wall or equipment.
  - 3.5 in between parallel connections or terminal blocks.

16.2 With Wire Duct

16.2.1 Wire duct to be Panduit type F or equal. Wires and cable shall not exceed 40% of the duct inside cross-sectional area at initial design.

16.2.2 The following are minimum recommended distances for wiring connections with wire duct:

- - 2.0 in between the connection or single level terminal and the wiring duct.
  - 1.5 in between multiple level terminal blocks and the wiring duct.

17. Environmental/Purging

17.1 All enclosures with internal heat generating devices (for example, transformers or instruments) shall be studied to verify if such devices produce enough heat to exceed the operating conditions of enclosure equipment. Enclosures that generate heat in excess of operating conditions of internal equipment shall have a heat exchanger or an air conditioner. Actual requirements shall be discussed with the lead engineer for correct selection.

17.2 Enclosures located in corrosive and/or dirty areas may be purged with dry air or nitrogen as long as the enclosure is supplied with a pressure relief device set at or below 0.5 psig. If it can be shown that it is not possible to build pressure in the enclosure (for example, because of cable entrance openings), then the pressure relief device can be omitted. It is also good practice to supply the enclosure with air or nitrogen regulated to a pressure less than 1 psig.

17.3 When enclosures are purged for environmental conditions, one volume change per hour shall be considered as the normal flow rate. All purges must at least have a manual shutoff.

17.4 Any enclosure purged with nitrogen shall have a sign stating that the enclosure is purged with nitrogen and that it is an asphyxiant. Enclosures that are large enough for an individual to have their head in the enclosure for maintenance purposes shall have an interlocked nitrogen supply source solenoid shutoff valve with the door, as well as a manual shutoff valve. The solenoid valve can be mounted internally but the manual nitrogen shutoff valve must be external to the enclosure. The warning nameplate shall be Orange (166) background with black letters and should read:

WARNING

Asphyxiant Hazard

This panel is nitrogen purged. The purge is automatically shut off when the door is opened. When working on this enclosure, also close the manual nitrogen shutoff valve.

17.5 Any enclosure purged with nitrogen shall have a sign stating that the enclosure is purged with nitrogen and that it is an asphyxiant. Enclosures that have only a manual shutoff external to the enclosure shall have a warning nameplate with a Red background with black letters and should read:

DANGER

Asphyxiant Hazard

This panel is nitrogen purged. The purge must be manually shut off before the door is opened.

17.6 Enclosures located outdoors and exposed to extreme temperature variances can accumulate condensate and therefore require a condensate drain/breather. Install a drain/breather that will safely remove water from the inside, and protect against water entry from the outside.

17.7 When mounting enclosures outdoors in cold environments, the installation of a heater might be required to keep internal devices at proper operating temperatures. Heaters shall be purchased with fans and installed with thermostats to maintain the enclosure at the proper operating temperature. They shall be mounted a minimum of 2″ from plastic devices, and wiring and consideration must be given to mounting location near temperature-sensitive instruments.

17.8 If thermal insulation is required, it shall be mounted on the internal surfaces of the enclosure and supported by mechanical means. Adhesives can be used by mechanically supporting insulation, and is preferred. Avoid metal backed insulations that may fall and come in contact with current-carrying parts. The insulation must be spaced 1/2″ or more from uninsulated live parts and 12″ or more from arcing parts.

18. TUBING

18.1 When introducing a pressurized source into an enclosure if not supplied with a condensate drain, a pressure relief means must be provided for the enclosure set at 5″ H₂O or less. Do not introduce flammable gases into enclosures with electrical equipment.

18.2 The panel supplier shall route panel tubing such that all instruments are accessible for in-place maintenance and removable for shop maintenance. The tubing shall be securely supported, paying particular care that the supports prevent noticeable movement of the tubing when block and bleed valves are operated. Process tubing, with a listed test pressure in excess of 150 psig, must be positively secured using bolted, metallic clamps within 6 to 12 inches of each compression connection. This is a mandatory safety requirement.

18.3 Vents on regulators located in a panel that control caustic or panel damaging gas shall be vented outside. A one to one pneumatics relay can be used if lines originate outside of the cabinet.

18.4 Exhausts of solenoids located internal to the panel are preferred to be vented outside of the enclosure. If not, relief sizing should be calculated.

18.5 Liquids are not permitted to be in the cabinet unless for sampling.

18.6 Synthetic

18.6.1 Nylon tubing is the preferred material to use in all control enclosures for reasons of cost, safety (nonconductive), and ease of installation. Preferred standard sizes are: 1/4, 3/8, and 1/2 in OD. The material shall be designated as Nylon 12 as supplied by Type TIA, of SMC Pneumatics Inc or equal.

18.6.2 The use of synthetic tubing shall be restricted to nitrogen, air, and other gases or fluids that are inert, nontoxic, nonflammable, and noncorrosive if possible. Certain chemical applications may require PFA (Perfluoroalkoxy) tubing.

18.6.3 Nylon tubing shall be used in service from 32° to 140°F, for design pressures less than 100 psig.

18.6.4 Polyurethane or polyethylene tubing may be used. Polyurethane has a much lower bursting pressure than nylon and care should be used at installation to avoid kinking or twisting. Polyethylene also has a lower bursting pressure than nylon.

18.7 Copper

18.7.1 The use of copper tubing shall be restricted to oxygen, nitrogen, air, argon, hydrogen, methane, glycol, water, and other gases or fluids that are nontoxic and noncorrosive. (Even trace quantities of certain corrosive contaminants might preclude the use of copper.)

18.7.2 Copper tubing may not be used in service above 205C (400F) nor for design pressures in excess of those tabulated on Table 1 of 4PS52001A.

18.8 Stainless Steel

18.8.1 Stainless steel tubing shall be used in all control panels not meeting the criteria set forth by paragraphs 18.7.1 and 18.7.2.

18.8.2 Maximum pressure rating shall not exceed 172 bar g (2500 psig) based on temperature of 150 °C (300F).

19. Fittings

19.1 All compression fittings for metallic tubing shall be Swagelok or Parker A-Lok. Mixing of compression parts from tubing compression manufacturers is prohibited.

19.2 One–touch fittings for nylon tubing shall be Type KQ2 from SMC Pneumatics, Inc or equal.

19.3 Hose barbs are permitted with polyurethane only.

19.4 Mixing of compression fitting materials (that is, brass and stainless steel) at a transition joint between copper and stainless steel tubing systems is prohibited. Transitions between tubing materials shall be accomplished by means of screw fittings, such as bulkhead fittings.

19.5 Brass precision pipe fittings shall be manufactured by the Swaglok Company or equivalent.

VALVES

20.1 Valves shall be installed in process and pneumatic tubing as indicated on the contract drawings and shall be located as close as possible to the instruments. Valves must match pressure and tubing materials. Whitey is the preferred supplier of valves.

21. Tube Cleaning

21.1 All tubing shall be cleaned as specified in the contract drawings. Refer to cleaning standards 4WPI-SW70001, 4WPI-SW70002, 4WPI-SW70003, and 4WPI-SW70004. Refer to 01.20.10 for approved cleaning agents. Other standards such as electronics UHP, 4WPI-FWSE01 may apply.

21.2 Instruments in such service will be furnished “oxygen cleaned and packaged” by Air Products. The panel supplier shall protect these instruments from contamination during assembly.

22. Pressure Testing

22.1 All back of panel tubing and piping shall be subjected to a pressure test to ensure that all joints are tight. The test may be witnessed by an Air Products representative who shall be notified three days before actual testing. Compressed nitrogen shall be provided by the panel supplier for such testing, together with all other equipment required to perform such tests in complete safety.

22.2 The panel supplier shall be responsible for pressure testing. Gases and pressures to be used for testing shall be verified by engineering.

23. Instrument Air Filtering

23.1 Incoming air/nitrogen supply for instrument air shall have a filter of no larger than 5 micron.

23.2 Solenoid and panel instrument air exhausts shall have a diffuser or filter to keep insects out and prevent flying projectiles from exiting.

24. Nameplates and Labels

24.1 All face of panel instrumentation and control devices such as push buttons, selector switches, indicating lights, and displays shall be labeled with a legend plate indicating the function and the name or number of the equipment or device controlled or displayed. Control devices shall be tagged according to the electrical schematics. All exterior panel nameplates can be adhered with 3M Plastic and Emblem Adhesive, number 08061. Stainless steel screws can be used but sealant on the threads must be used to maintain NEMA integrity.

24.2 All indicators with multiple points shall have one large nameplate, identifying each point.

24.3 The following nameplate type shall be selected from 530-SD-129, white with black core:

Type “AP1” single function.

Type “RPI” multiple point function (for example, recorders).

24.4 All control panels shall have a face of panel nameplate, identifying the panel number and its function. The nameplate can also include the drawing number of the panel, highest voltage present, and if fed from multiple sources. Electrical requirements may need to be added to separate nameplate to meet individual customer requirements for color.

24.5 Tubing exiting an enclosure shall have a label identifying the bulkhead connection number, the equipment number of the device it is supplying, or the equipment number of the device supplying the pressure.

24.6 Panel interior instrumentation and control devices can be labeled with engraved nameplates or adhesive backed mylar. See contact drawings if required. Control devices shall be tagged according to the electrical schematics.

24.7 UL label requirements will require additional labeling.

25. Painting

25.1 All enclosures shall be specified primed and painted by their respective manufacturers whenever possible. Standard color should be as close as possible to ANSI 61 (grey). Equipment or customer paint requirements can supersede this paragraph.

25.2 Custom painted enclosures shall be painted to Painting and Corrosion Protection of New Construction for Design Temperatures.

25.3 Primer only panels shall not be installed in the field. Primed panels should only be purchased for painting another color.

26. Inspection

26.1 The panel may be inspected by an QC inspector before shipment. Panel vendor must contact Air Products upon completion of panel. If inspected, panel vendor will provide necessary power and work area for the inspector. Assistance shall also be provided by the panel vendor during inspection if required. The control panel will be inspected per drawings (power applied as well) by the panel vendor before Air Products inspection. All deviations determined in this inspection will be corrected before the Air Products inspection.

26.2 The panel inspector may direct up to 10 percent random disassembly of tubing and instruments to verify cleaning. The panel supplier shall perform this work at no extra cost to Air Products. If the sampled components do not meet the standards, 100 percent recleaning shall be required at no extra cost.

27. Shipping

27.1 Packing: The panel shall be packaged in a polyethylene material and/or crated to ensure protection from damage as a result of shipping or exposure to the weather.

27.2 If the panel has lifting lugs installed, they should be accessible for use in offloading the panel at the field site.

27.3 After packaging and/or crating, the panel shall be shipped using the “Air Ride” method.

27.4 Spare parts and supplier literature shall be placed in a sturdy cardboard box, properly protected with packing material, and securely taped with metal duct tape to the control floor.

27.5 All panel openings shall be sealed (caps or plugs installed) for shipment with the appropriate plug or cover. Panel fan and exhaust openings shall have plastic sheeting installed behind the fan or filter grill. Taping over cutouts, conduit fittings, and bulkhead connections is not permitted.

27.6 If shipping internationally, additional requirements are needed.