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Application Data Industrial Automation Wiring and Grounding Guidelines Purpose This publication gives you general guidelines for installing an Allen-Bradley industrial automation system that may include programmable controllers, industrial computers, operator-interface terminals, display devices, and communication networks. While these guidelines apply to the majority of installations, certain electrically harsh environments may require additional precautions. Use these guidelines as a tool for helping avoid potential electromagnetic interference (emi) and transient emi that could cause problems such as “adapter faults, rack faults, communication faults,” etc. These guidelines are not intended to supersede local electrical codes. This publication is organized into the following sections: • Raceway layout considerations • Mounting, bonding, and grounding • Power distribution • Surge-suppression • Ferrite beads • Enclosure lighting • Avoiding unintentional momentary turn-on of outputs • Related publications Publication 1770-4.1 – February 1998 2 Industrial Automation Wiring and Grounding Guidelines Raceway Layout Considerations The raceway layout of a system is reflective of where the different types of I/O modules are placed in I/O chassis. Therefore, you should determine I/O-module placement prior to any layout and routing of wires. However, when planning your I/O-module placement, segregate the modules based upon the conductor categories published for each I/O module so that you can follow these guidelines. Also, all conductors (ac or dc) in the same raceway must be insulated for the highest voltage applied to any one of the conductors in the raceway. These guidelines coincide with the guidelines for “the installation of electrical equipment to minimize electrical noise inputs to controllers from external sources” in IEEE standard 518-1982. Categorize Conductors Segregate all wires and cables into the following three categories (Table A). Refer to the publication for each specific I/O module or block for individual conductor-category classification of each I/O line. Table A Follow these Guidelines for Grouping Conductors with Respect to Noise Group conductor cables fitting this description Into this category: Examples: Control & ac Power — high-power conductors that are Category 1 more tolerant of electrical noise than category 2 conductors and may also cause more noise to be picked up by adjacent conductors • corresponds to IEEE levels 3 (low susceptibility) & 4 (power) • ac power lines for power supplies and I/O circuits. • high-power digital ac I/O lines — to connect ac I/O modules rated for Signal & Communication — low-power conductors that Category 2 are less tolerant of electrical noise than category-1 conductors and should also cause less noise to be picked up by adjacent conductors (they connect to sensors and actuators relatively close to the I/O modules) • analog I/O lines and dc power lines for analog circuits • low-power digital ac/dc I/O lines — to connect to I/O modules that are • corresponds to IEEE levels 1 (high susceptibility) & 2 (medium susceptibility) high power and high noise immunity • high-power digital dc I/O lines — to connect dc I/O modules rated for high power or with input circuits with long time-constant filters for high noise rejection. They typically connect devices such as hard-contact switches, relays, and solenoids. rated for low power such as low-power contact-output modules • low-power digital dc I/O lines — to connect to dc I/O modules that are rated for low power and have input circuits with short time-constant filters to detect short pulses. They typically connect to devices such as proximity switches, photo-electric sensors, TTL devices, and encoders • communication cables (ControlNett, DeviceNett, Universal remote I/O, extended-local I/O, DH+, DH-485, RS-232-C, RS-422, RS-423 cables) — to connect between processors or to I/O adapter modules, programming terminals, computers, or data terminals Intra-enclosure — interconnect the system components Category 3 within an enclosure • low-voltage dc power cables — provide backplane power to the • corresponds to IEEE levels 1 (high susceptibility) & • communication cables — to connect between system components 2 (medium susceptibility) system components within the same enclosure NOTE: Remote I/O and DH+ cables must be made of catalog number 1770-CD cable or a cable from the approved-vendor list (publication ICCG-2.2). DH-485 cables must be made of a cable from the approved-vendor list in publication 1770-6.2.2. Publication 1770-4.1 – February 1998 Industrial Automation Wiring and Grounding Guidelines 3 Route Conductors To guard against coupling noise from one conductor to another, follow these general guidelines (Table B) when routing wires and cables (both inside and outside of an enclosure). Use the spacing given in these general guidelines with the following exceptions: • where connection points (for conductors of different categories) on a device are closer together than the specified spacing • application-specific configurations for which the spacing is described in a publication for that specific application These guidelines are for noise immunity only. Follow all local codes for safety requirements. Table B Follow these Guidelines for Routing Cables to Guard Against Noise Route this category of conductor cables: According to these guidelines: Category 1 These conductors can be routed in the same cable tray or raceway with machine power conductors of up to 600V ac (feeding up to 100 hp devices). Category 2 • If it must cross power feed lines, it should do so at right angles. • Route at least 5 ft from high-voltage enclosures, or sources of rf/microwave radiation. • If the conductor is in a metal wireway or conduit, each segment of that wireway or conduit must be bonded to each adjacent segment so that it has electrical continuity along its entire length, and must be bonded to the enclosure at the entry point. • Properly shield (where applicable) and route in a raceway separate from category-1 conductors. • If in a contiguous metallic wireway or conduit, route at least 0.08m (3 in) from category-1 conductors of less than 20A; 0.15m (6 in) from ac power lines of 20A or more, but only up to 100 kVA; 0.3m (1 ft) from ac power lines of greater than 100 kVA. • If not in a contiguous metallic wireway or conduit, route at least 0.15m (6 in) from category-1 conductors of less than 20A; 0.3m (1 ft) from ac power lines of 20A or more, but only up to 100 kVA; 0.6m (2 ft) from ac power lines of greater than 100 kVA. Category 3 Route conductors external to all raceways in the enclosure or in a raceway separate from any category-1 conductors with the same spacing listed for category-2 conductors, where possible. Important: These guidelines assume that you follow the surge-suppression guidelines (page 15). While these guidelines apply to the majority of installations, certain electrically harsh environments may require additional precautions. The use of the guidelines in Table B are illustrated in Figure 1. Publication 1770-4.1 – February 1998 4 Industrial Automation Wiring and Grounding Guidelines Figure 1 Mounting Assembly Details Category-2 Conductors Category-1 Conductors (ac Power Lines) Conduit Tighter spacing allowed with conduit Conduit Enclosure Wall Use greater spacing without conduit Transformer Tighter spacing allowed where forced by spacing of connection points Category-2 Conductors I/O Block 1771 I/O Chassis Place modules to comply with spacing guidelines if possible Mounting, Bonding, and Grounding Publication 1770-4.1 – February 1998 12618-I After establishing all layouts, you can begin mounting, bonding, and grounding each chassis. Bonding is the connecting together of metal parts of chassis, assemblies, frames, shields, and enclosures to reduce the effects of emi and ground noise. Grounding is the connection to the grounding-electrode system to place equipment at earth ground potential. Industrial Automation Wiring and Grounding Guidelines 5 Mounting and Bonding the Chassis You can mount the chassis with either bolts or welded studs. Figure 2 shows details for: • stud-mounting a ground bus or chassis to the back panel of the enclosure • stud-mounting a back panel to the enclosure • bolt-mounting a ground bus or chassis to the back panel of the enclosure If the mounting brackets of a chassis do not lay flat before the nuts are tightened, use additional washers as shims so that the chassis does not bend when you tighten the nuts. Important: Do not bend the chassis. Bending the chassis might damage the backplane and result in poor connections. Figure 2 Mounting Assembly Details Back Wall of Enclosure Back Panel Mounting Bracket or Ground Bus Welded Stud Flat Washer Scrape paint Nut Back Panel Welded Stud Nut Flat Washer Star Washer If the mounting bracket is coated with a non-conductive material (anodized, painted, etc.), scrape the material around the mounting hole. Stud mounting of a ground bus or chassis to the back panel Use a wire brush to remove paint from threads to allow a ground connection. Scrape paint on panel and use a star washer. Stud mounting of the back panel to the enclosure back wall 17666 Back Panel Tapped Hole Ground Bus or Mounting Bracket 17664 Back Panel Bolt Mounting Bracket Tapped Hole Flat Washer Nut Star Washer Flat Washer Scrape paint on panel and use star washers. Nut Scrape paint Flat Washer Flat Washer If the mounting bracket is coated with a non-conductive material (anodized, painted, etc.), scrape the material around the mounting hole. Bolt mounting of a ground bus or chassis to the back panel Star Washer 17665 Bolt If the mounting bracket is coated with a non-conductive material (anodized, painted, etc.), scrape the material around the mounting hole. Alternative bolt mounting of chassis to the back panel 12342-I Publication 1770-4.1 – February 1998 6 Industrial Automation Wiring and Grounding Guidelines Make good electrical connection between each chassis, back-panel, and enclosure through each mounting bolt or stud. Wherever contact is made, remove paint or other non-conductive finish from around studs or tapped holes. Bonding and Grounding the Chassis With solid-state controls, proper bonding and grounding helps reduce the effects of emi and ground noise. Also, since bonding and grounding are important for safety in electrical installations, local codes and ordinances dictate which bonding and grounding methods are permissible. For example, for U.S. installations, the National Electrical Code (NEC) gives you the requirements for safe bonding and grounding, such as information about the size and types of conductors and methods of safely grounding electrical components. Equipment-Grounding Conductor — In addition to making good connections through each bolt or stud, use either 1-inch copper braid or 8 AWG minimum stranded copper wire to connect each chassis, enclosure and central ground bus mounted on the back-panel. Figure 3 shows ground-bus connection details. Figure 3 Ground Bus Connection Details Ground Bus Mounting Ground Bus Equipmentgrounding Conductors Ground Lug Tapped Hole Star Washer Bolt Grounding-electrode conductor to grounding-electrode system. 13271 Figure 4 shows enclosure-wall ground connection details. Use a steel enclosure to guard against emi. If the enclosure door has a viewing window, it should be a laminated screen or a conductive optical substrate to block emi. Do not rely on the hinge for electrical contact between the door and the enclosure; install a bonding wire. Publication 1770-4.1 – February 1998 Industrial Automation Wiring and Grounding Guidelines 7 Figure 4 Details of Ground Connection at Enclosure Wall Enclosure Wall Scrape Paint Bolt Ground Lug Scrape paint on enclosure wall and use a star washer. Nut Star EquipmentWasher Grounding Conductor 10020 Connect an equipment grounding conductor directly from each chassis to an individual bolt on the ground bus. For a chassis with no ground stud, use a mounting bolt (Figure 5). For those chassis with a ground stud, use the ground stud for this connection (Figure 6). Figure 5 Details of Ground Connection at Mounting Bracket of Chassis with No Ground Stud Back Panel Mounting Bracket Welded Stud Scrape paint Ground Lug Flat Washer Nut Flat Washer Star Washer If the mounting bracket is coated with a non-conductive material (anodized, painted, etc.), scrape the material around the mounting hole. 17666 For a power supply without a groundable power supply chassis (such as a power-supply module or mini-processor with an integral power supply), or a power supply (such as the 1771–P7 or 1771–PS7) with a chassis that is not internally connected to its GND terminal, use a 14 AWG copper wire to connect its GND terminal to the ground stud or mounting bolt connected to the ground bus. This will ensure an adequate ground for noise immunity. Publication 1770-4.1 – February 1998 8 Industrial Automation Wiring and Grounding Guidelines Figure 6 Typical Grounding Configuration Enclosure Wall See Figure 3 See Figure 4 Ground Bus Groundingelectrode Conductor To Groundingelectrode System 1756 Chassis with 1756-PA72 Power Supply Equipment-grounding Conductors 8AWG Equipment-grounding Conductors 14AWG FLEX I/O Modules DIN Rail 1771-P7 Power Supply 1771 Chassis with 1771-P7 Power Supply I/O Chassis Wall 14 AWG Mini-processor with built-in power supply Ground Lug Nut Power-supply module Star Washers 1771 Chassis with 2 Power Supplies Ground Lug Star Washer 14 AWG Ground Bus 15317 Do not lay one ground lug directly on top of the other. This type of connection can become loose due to compression of the metal lugs. Sandwich the first lug between a star washer and a nut with a captive star washer. After tightening the nut, sandwich the second lug between the first nut and a second nut with a captive star washer. Publication 1770-4.1 – February 1998 Industrial Automation Wiring and Grounding Guidelines 9 Some products have no visible groundable chassis and no ground lug or ground terminal, but mount on a DIN rail. The FLEX I/O products are in this category. The chassis of these products are grounded only thru the DIN rail. For these products, connect an equipment-grounding conductor directly from the mounting bolt on the DIN rail to an individual bolt on the ground bus. Grounding-Electrode Conductor — Connect the ground bus to the grounding-electrode system through a grounding-electrode conductor. The grounding-electrode system is at earth-ground potential and is the central ground for all electrical equipment and ac power within any facility. Use 8 AWG copper wire minimum for the grounding-electrode conductor to help guard against emi. The National Electrical Code specifies safety requirements for the grounding-electrode conductor. Shielded Cables — Certain I/O connections require shielded cables to help reduce the effects of electrical noise coupling. Ground each shield at one end only. A shield grounded at both ends forms a ground loop which can cause a processor to fault. Ground each shield at the end specified in the appropriate publication for the product. Never connect a shield to the common side of a logic circuit (this would introduce noise into the logic circuit). Connect each shield directly to a chassis ground. For some communication network cables, the shield connections are unique to the particular cabling system. In some such cases, a dc short to ground is not needed because a low-impedance ac path to ground and a high-impedance dc path to ground are provided internally at each node. Follow the specific instructions in the publication provided for the specific communication network cabling system. Avoid breaking shields at junction boxes. Many types of connectors for shielded conductors are available from various manufacturers. If you do break a shield at a junction box, do the following: • Connect only category-2 conductors in the junction box. • Do not strip the shield back any further than necessary to make a connection. • Connect the shields of the two cable segments to ensure continuity along the entire length of the cable. Publication 1770-4.1 – February 1998 10 Industrial Automation Wiring and Grounding Guidelines You can connect the power supply directly to the secondary of a transformer (Figures 7 and 8). The transformer provides dc isolation from other equipment not connected to that transformer secondary. Connect the transformer primary to the ac source; connect the high side of the transformer secondary to the L1 terminal of the power supply; connect the low side of the transformer secondary to the neutral (common) terminal of the power supply. Power Distribution Figure 7 Grounded ac Power-Distribution System with Master-Control Relay Disc. Suppressor1 1FU L1 L1 2FU Incomming L2 ac L2 3FU L3 To Motor Starters Enclosure Wall L3 H4 H1 H3 H2 Back-panel Ground Bus Step-down 2 Transformer Grounded Conductor FUSE Multiple E-stop switches Grounding-electrode Conductor to Grounding-electrode System X2 X1 Start CRM EquipmentGrounding Conductors Suppressor1 CRM L1 The I/O circuits form a net inductive load switched by the CRM contacts. Therefore, a suppressor is needed across the line at the load side of the CRM contacts. Controller Power Supply GND Connect when applicable N or L2 User dc Supply CRM Suppressor3 Input Module Wiring Arm Input Sensor Ouput Actuator Output Module Wiring Arm CRM + - To dc I/O actuators/ sensors Notes: 1 To minimize emi generation, connect a suppressor across an inductive load. For suppressors to use, refer to 11 and C or the Electrocube catalog. 2 In many applications, a second transformer provides power to the input circuits and power supplies for isolation from the output circuits. 3 Connect a suppressor here to minimize emi generation from the net inductive load switched by the CRM contacts. In some installations, a 1mf 220W suppressor (Allen-Bradley 700-N5) or 2mf 100W suppressor (Electrocube PN RG1676-7) has been effective. For suppressors to use, refer to Figure 11 and Table C or the Electrocube catalog. Publication 1770-4.1 – February 1998 19241