Grounding Design Guide for Electric Power Generation Products {4450, 4459} Caterpillar

Electric Power Generation

All

Generator Set

All

Introduction

This document offers guidance in grounding generator set packages to provide protection for operators and users. The ground provides a common reference between the generator set, the controls, and the components that are located in various locations that are on and off the package. Proper grounding is also required to meet compliance to regulations and the functionality.

This document is intended for Caterpillar and dealer personnel that are involved in the design, the application, the installation, and/or the commissioning procedures of Electric Power Generation products.

Proper grounding protects personnel and equipment from the following events:

• Ground fault that causes a shock hazard

• Lightning

• Opening of the vacuum circuit breaker

• Large load swings

• Equipment failure

Requirements in this document reflect the following information: codes, standards, relevant legislation, and experience in design.

Terminology

Recommendations are indicated by the following term:

• Should

Requirements are indicated by the following terms:

• Must

• Shall

Scope

The scope of this document is for Electric Power Division products. The following products are included:

• Generator Sets (open and enclosed)

• Power Modules

• Controls

This document provides guidelines for grounding AC electrical generator sets and associated components. These recommendations should be followed to ensure compliance with international standards and major regional standards.

The following applications may have special requirements that are not covered in this document: marine, petroleum, and locomotive.

Responsibilities

Caterpillar is responsible for designing and delivering a product that conforms to this specification.

The dealer is responsible for installing the generator set package to meet the applicable local requirements. Additions and/or modifications to the basic ground system for the satisfaction of local codes are the responsibility of the dealer.

A qualified engineer is required for the design and the commissioning of all installations and applications of customer generator sets. Qualified engineers must be Professional Engineers (PE), Engineers of Record, or Equivalent responsible individuals.

The customer is responsible for maintaining and repairing the grounding system and all equipment on the generator set package.

The customer is responsible for ensuring that the quality of the earth ground is tested periodically.

Site Grounding

Customer Connections

The customer is responsible for connecting the customer ground connection on the generator set to the ground plane for the facility power. The ground conductor must be sized and installed in accordance with the applicable local codes. At a minimum, this ground conductor will be the same size as the neutral to ground cable. Metallic conduit shall not be used as an equipment ground anywhere in these circuits. Periodic testing of this ground connection is highly recommended. Annual periodic testing is the minimum requirement.

Shore Power Grounding

Shore power grounding shall include a separate equipment ground conductor that is sized and installed in accordance with the applicable local codes. Metallic conduit shall not be used as an equipment ground anywhere in these circuits.

Local Codes

Comply with all local ordinances and with all authorities that have jurisdiction. The dealer is responsible for ensuring that there is compliance with the local codes.

Switch Gear

• An engineering review is required to ensure a proper grounding system.

• Tie the normal distribution system grounds and emergency distribution system grounds together when you are required by local codes. Refer to the locally applicable codes for details.

• Since the switch gear is typically tied into the generator set controls, it is important for the customer switch gear to be connected to the same ground plane and/or the same ground system.

• Use caution with separately derived neutral systems.

• Label the grounding system in accordance with the applicable local codes.

Ground Plane

All ground planes and all ground systems shall be electrically connected. Periodic inspections and tests are required to avoid circulating ground currents. In the locations that the soil alone will not provide an adequate ground plane, the soil shall be supplemented to ensure an effective ground plane. Never establish a ground plane that is independent of the ground plane or the ground system that is used by the connected load under normal power conditions.

Package Grounding

Ground Connections

Cable Terminations

Termination of all ground cables must be with 1-hole ring terminals or 2-hole ring terminals. The terminals are required to be sized accordingly to the cable size and current carrying requirements.

All ground cables shall be terminated with ring terminals (single or double hole) that are suitable for bolting the terminal to the mating surface. Terminals shall be sized according to the cable size and current requirements.

Stacking Of Multiple Ring Terminals

The entire contact surface of the ring terminal is required to have solid contact with any frame or any ring terminal that is adjacent below the ring terminal.

The transition from the crimp or the clamp that is holding the wire to the ring of the ring terminal is not flat.

All stacked ring terminals are required to be the same size. If various sizes of ring terminals are used, the clamping force that is necessary for the largest ring terminal may exceed the maximum clamping force of the smallest ring terminal.

The clamping force of the nut that is holding the rings in place is required to be high enough to prevent the cable from loosening due to moving ground cables.

All threaded fasteners are required to be tightened to the individual torque specifications.

Termination Contact Surfaces

All contact surfaces are required to be bare metal. The use of a corrosion inhibitor is recommended.

The contact surface shall be integral to the structure that is being grounded. The studs and bolts that are used to fasten the ground cable are not an intended path for current. If the studs and bolts are used in this manner, the connection must be tested per the instructions in this document. Studs that are welded to the enclosure can be used to provide joints for bonding to an earth ground only if contact is made with bare metal of the frame.

The contacting surfaces are required to be compatible metals to minimize the effects of electrolysis and the effects of corrosion.

Cables

All ground cables are required to have multiple strands.

Cable Size

All cables for bonding to ground are sized per Table 1 except for the following connections:

• Neutral to ground connection (connection point for the customer)

• Connection point for the customer for connection to the ground plane of the facility

The connections in the above list are sized per the "Generator Neutral Ground" section. The size of the ground bonding cables is based on the potential fault currents of the circuit. Refer to Table 1 for the sizes of the bonding cables. Multiple cables of the same size are acceptable if the total current rating of the combined cables is equal. Multiple cables of the same size are acceptable if the total current rating of the combined cables exceeds the rating of the single cable that is listed in Table 1.

Customer Ground Connection

One single location shall be defined for the customer to provide an earth ground. The location for the earth ground is required to have a label with the following information: ISO symbol number 5019 (IEC 60417). The location for the earth ground shall not be accessible from outside of the package. Bare metal is required for the customer earth ground connection. The conductor that is used to connect the earth ground to the customer connection location on the package (UL 2200, section 15.5) should be equal to or greater than the size of the generator neutral to the ground conductor. All generator package component grounds are required to branch from this connection in a star distribution.

Generator Frame

The generator frame is required to be connected to the customer ground connection. The connection shall be made with one or more cables.

Mounting Structures (Base or Rails)

Separate ground straps or cables should ground the mounting structures to the customer ground connection. Direct contact and/or bolted joints with the generator and the engine may be sufficient. However, the connections are required to be tested periodically. The bonding cable shall be sized to carry the maximum potential value of fault current that is seen by the mounting structure in the case of a ground fault.

Isolated mounting systems

A ground strap is required for components that are mounted on nonconductive vibration mounts in cases when these components are not already bonded to the customer ground connection by other means. Nonconductive vibration mounts are not reliable for conducting current. Ground straps must not be installed in the location that will create a ground loop. The bonding cable(s) shall be sized to carry the maximum potential of fault current that is seen by the mounting structure in the case of a ground fault.

Refer to Table 1 for sizing the cable.

Engine Block

The structural components of the engine should not be used as a current conductor. The engine block is an example of a structural component. The contact surfaces between a close coupled generator and the engine are machined surfaces. These surfaces are not painted. This offers some means to provide a ground path between the generator and the engine. These contact surfaces should be tested periodically. If the resistance from the engine block to earth ground is unacceptable, a separate ground cable between the engine block and the customer ground connection location is required. The bonding cables shall be sized to carry the maximum potential fault current that is seen by the mounting structure in the case of a ground fault.

Refer to Table 1 for sizing the cable.

Generator Neutral Ground

Grounding the neutral is frequently mandated by national codes and local codes. Equipment grounding is also recommended in cases when grounding the neutral is not required.

The method that is used to ground a generator neutral is required to be chosen as part of the overall design of the system. Medium voltage generator neutrals and high-voltage generator neutrals are typically grounded through a resistance or inductance providing added protection for the generator windings by limiting the fault current during line to ground faults and reduce the magnitude of the transient over voltages. The neutral on low voltage generators is typically connected to ground. Refer to the "IEEE Std 142" for more information on neutral grounding.

The following chart outlines the requirements of the cable sizes. The "Standards" for these requirements can be found in the "Standards" section of this manual. The requirements of the cable are based on the generator output capabilities.

Battery Negative

Connect a cable between the battery negative connection point and the location of the customer ground connection. The minimum size of this cable is required to be 12 AWG ( 4mm² CSA). An in-line battery disconnect switch may be provided between the negative post of the battery and the point of common battery negative contact.

Starters

Make the cable between the starter negative post and the battery negative post as short as possible to minimize the opportunity to transfer electrical noise that is generated by the starter. Additionally, the short length of cable is necessary to minimize the voltage drop. The case of the starter should be isolated from the DC circuit. Additionally, the case of the starter should be connected to the customer ground connection location separately from the battery negative ground.

Charging Alternators

A direct connection is required from the negative post of the charging alternator to the common connection point of the battery negative. Do not use this connection for a customer connection. Do not rely on the engine block for carrying the current. The case of the charging alternator should have a separate cable to the customer ground connection location or the case of the alternator should be isolated from the engine block if the case of the charging alternator is connected internally to the negative terminal.

Voltage Regulator

The chassis of the voltage regulator is required to be connected to earth ground at the customer ground location. The ground cable is required to be the same size as the largest power input cable to the regulator. The chassis ground may be accessible via a terminal on the device.

Load Share Module

The load share module chassis is required to be connected to customer ground connection location. The ground cable is required to be the same size as the largest input cable to the loadshare module. The chassis ground may be accessible via a terminal on the device.

Package Mounted Sensors And Actuators

The sensors and the actuators that are mounted on the generator set should have individual signal connections, power connections, and ground connections. New product designs shall only use sensors or actuators that have individual signal connections, power connections, and ground connections.

Generator Space Heater

The generator space heaters are connected to external utility power. The connection is usually through a generator terminal strip that is sized appropriately for the load requirements. This external utility connection is required to be grounded according to local codes and requirements.

Jacket Water Heater

The jacket water heaters are connected to external utility power. The connection is usually through a generator terminal strip that is sized appropriately for the load requirements. This external utility connection is required to be grounded according to local codes and requirements.

If a ground connection on the jacket water heater is present, a connection to the customer ground connection location is required. Do not connect the ground connection on the jacket water heater to the utility ground.

Battery Charger

The case for the battery charger is required to be insulated from the internal components. This case is required to be connected to the customer ground connection location on the package. This case is not required to be connected to the utility ground. The negative output of the battery charger shall not be connected to ground within the battery charger.

Sheet Metal, Terminal Box, And Package Mounted (Control) Enclosures

Extension boxes should be grounded through a stud that is welded on the central terminal box.

Ground the removable sheet metal through a grounding stud that is welded on the enclosure or the frame of the terminal box. Refer to "Ground Bond Testing Requirements" for acceptability testing of the ground bond.

Control enclosures (package mounted) shall be grounded to the customer ground connection point. These connections can be direct or these connections can be through a common connection point in the control enclosure.

The design for the ground bonding is required to be based on the potential exposure of the enclosure to fault currents. If applicable, refer to Table 1 for size of the bonding cables.

Hinged Access Doors Or Panels

A separate bonding cable or a separate bonding strap is required for doors or access panels since the hinges are not reliable for ground bonding. This strap or cable may be connected to the adjoining panel or the adjoining frame.

Refer to Table 1 for the sizing of the cable or the sizing of the strap.

Utility Powered Electrical Systems

Utility powered electrical systems are required to be designed so that grounding of the systems is consistent with International codes and local codes. This ground may be separate from the ground of the generator set. These systems can be mounted on the package or these systems can be part of an enclosure or power module.

Enclosures (Canopy)

Drop-Over

Grounding to the customer ground connection location is required on the generator enclosure sheet metal.

Package Powered Electrical Systems

Package powered electrical systems are required to be bonded to the customer ground connection location.

Fuel Tank

Fuel tanks are required to be bonded. , Nonmetallic tanks are included in the tanks that need to be grounded. The bonding cable is required to have at least the same current carrying capacity as the neutral to ground conductor. The exception is the nonmetallic tank. In this case, a 12 AWG ( 4mm² CSA) conductor is sufficient. The cable connection to the fuel tank is required to be placed at a convenient location that is not adjacent to the following items: fuel inlet, fuel outlet, and the vent. The ground connection point is required to be isolated from fuel liquids or fuel vapors.

Trailers (Factory Supplied Or Dealer Packaged)

Utility Powered Electrical Systems

Utility powered electrical systems are required to be designed so that the grounding is consistent with International codes and local codes. This ground may be separate from the ground for the generator set.

Package Powered Electrical Systems

Package powered electrical systems are required to be bonded to the customer ground connection location.

Labeling (Identification) Of Ground Connections Or Cables

• All labels are required to use international symbols without text.

• The customer ground connection location must be marked with the ISO symbol number 5019 (IEC 60417). Only one location can be marked with a label (ISO symbol number 5019). The label is required to be visible after removal of the access panels, even when the cables are connected to the ground bar.

• ISO symbol 5017 may be used to designate various points within the unit that are bonded to ground. Do not use these points for customer ground connections.

• ISO symbol 5018 may be used to indicate signal ground that has the special characteristic for being noise free.

• Ground cables are required to be green with a yellow stripe that covers 30 percent to 50 percent of the insulating jacket. (IEC 60446, NFPA 70 section 250).

Other Package Mounted Attachments

• Utility powered electrical systems are required to be designed so that grounding of the systems are consistent with International codes and National codes. This ground may be separate from the ground for the generator set.

• The case of the attachments is required to be insulated from the internal components of the attachments. This case is required to be connected to the customer ground connection location.

• Package powered electrical systems are required to be bonded to the customer ground connection location. A separate cable back to the customer ground connection location is strongly recommended.

Ground Bond Testing Requirements

Any exposed metal part that contains energized equipment is required to be bonded to earth ground through the customer ground connection location. The impedance shall not exceed 100 milliohms.

This impedance shall be verified by passing a 25 Ampere AC current between the point that is in question and the customer ground connection.

Reference: UL 2200, Section 50 (July 7, 2004)

Remotely Located Components

Remotely Located Components should have an isolated case or chassis. Voltage regulators and load share modules are examples of components that can be remotely located.

The electrical circuits of all components that are located remotely are required to be part of the same ground reference as the generator set. For proper operation, the electrical circuits are required to have a common reference.

If the chassis of these devices is metal, the devices should be grounded in the remote location. If the chassis is not isolated from the circuit that is within the chassis, then special care must be taken to limit access to the circuit. Appropriate warnings must be provided.

Signal Grounding

EMCP

The EMCP electronic control is required to have a dedicated connection to the battery negative connection point.

All EMCP sensors must use shielded twisted-pair cable for connections back to the control (GSC). The shield must be grounded on the battery negative connection point on the EMCP.

If connectors are used between a sensor and the control, the shield of the two cables must be electrically connected together. Additionally, the shield must only be terminated at the battery negative connection point on the control.

ADEM

The ADEM control is required to have a dedicated connection to the battery negative connection point.

All ADEM sensors must use shielded twisted-pair cables for connections back to the control. The shield must be grounded on the battery negative connection point on the ADEM.

If connectors are used between a sensor and the control, the shield of the two cables must be tied together. Additionally, the shield must only be grounded to the battery negative connection point on the control.

Shielding

Shielding must be terminated only at the control end of the cable. Special exceptions may exist. These exceptions must be clearly documented as an exception.

Sensors

A sensor needs to have a signal path and a return path to the control that is supplied by the sensor.

Three-Wire Sensor

A three-wire sensor system uses a reference voltage in addition to the signal and the return.

Single-Wire Sensors

Single-wire sensors are discouraged because these sensors use the engine block or the generator as a current return path which can lead to engine failures.

Magnetic Pickups

The magnetic pickup must use shielded twisted-pair cable. The shield must be grounded at the battery negative connection point.

The connection between the mag pickup and the control should preferably be the following type of connection:

• A connection without breaks

• A connection with minimal length

• A connection that is not routed along side of other conductors.

If the connection must include a connector, the contact should be made with the use of high-quality contacts that are gold plated. The cable for the mag pickup should not be routed with other conductors that carry AC line voltage.

Thermocouple Wiring

Thermocouple wiring must use the appropriate wire type in a continuous run. Thermocouple wiring must be isolated from ground.

Actuators

Caterpillar recommends a dedicated return conductor when you are wiring the actuators. Using the engine block or the generator frame as a current return path must be avoided whenever it is possible to avoid potential engine failures.

Conductors

Caterpillar recommends separating the signal wiring from the AC cables to avoid noise coupling.

Maintenance

The grounding systems must be part of the maintenance plan of the generator set. A visual inspection that looks for corrosion must be combined with testing of the ground connections.

Grounding maintenance instructions must be included in the maintenance instructions.

References

Standards

• IEC/EN 60439

• IEC/EN 60204-1

• IEC 60446 (color codes)

• IEC 60417 (symbols)

• UL2200 (stationary generator sets - US)

• CSA-C22.2 No. 0.4-04 (grounding - Canada)

• NFPA 70 (NEC – US)

• IEEE Std 142 (the Green Book)

• IEEE Std C37.101

• IEEE Std C37.102

• IEEE Document 95TP102 (1995)

Other Publications

• A and I Guide BBBB-YYYY Pub in conjunction with Design Guide

Definitions

Bond - A reliable electrical connection between two conductive parts

Bonding (Bonded) - The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likely to be imposed (NFPA 70)

Bonding Conductor - A protective conductor providing electrical equipotential bonding (IEE Wiring Regulations -17th Edition)

Bonding Jumper - A reliable conductor to ensure the required electrical conductivity between metal parts required to be electrically connected (NFPA 70)

Customer Ground Connection Location - The Customer Ground Connection Location is the single location the customer must connect to for proper earth grounding of the package or enclosure. This connection point is in a protected location that is marked by the standard ISO symbol.

Earth - In this document, earth is the conductive mass of the earth. The electric potential at any point of earth is conventionally taken as zero. Earth is also called ground.

Earth Electrode (Rod) - The Earth Electrode (Rod) is the conductive part (for example a copper rod), which may be embedded in the soil or in a specific conductive medium, e.g., concrete or coke, in electrical contact with the earth. (IEE Wiring Regulations -17th Edition)

Earth Ground - The Earth Ground is a protective grounding circuit to Earth though an earth electrode (rod) or similar device.

Earthing - Earthing is the connection of the exposed-conductive-parts of an installation to the main earthing terminal of that installation.(IEE Wiring Regulations - 17th Edition).

Enclosure - The enclosure is the structure that contains the generator set. The enclosure may also contain the switchgear. The enclosure is also called a canopy.

Equipotential Bonding - Equipotential Bonding is the electrical connection maintaining various exposed-conductive-parts and extraneous-conductive-parts at substantially the same potential. (IEE Wiring Regulations - 17th Edition).

Generator Set Ground - Generator Set Ground is an alternative term that refers to the customer ground circuit and the ground bonds that are connected to customer ground circuit on the generator set.

Ground - Ground is an electricity conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth or to some conducting body that serves in place of the earth. (NEC, NFPA 70)

Ground Bond - Ground Bond is the protective bond between any exposed or conductive parts of the generator set, ultimately connected to the customer ground connection point. The Ground Bond is intended to carry a fault current internal to the generator set.

Ground Strap - A Ground Strap is a cable that is used to create a ground bond.

Ground(ing) System - The Ground System is the complete protective ground circuit of an installation such as a generator set with all of its controls, an entire powerhouse, or a complete facility.

Grounded - The term Grounded refers to connections to earth or to some conducting body that serves in place of the earth. (NFPA 70)

Grounding Conductor - A Grounding Conductor is a conductor that is used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes. (NFPA 70)

Grounding Conductor, Equipment - The Grounding Conductor for the equipment is the conductor that is used to connect the non-current carrying metal parts of equipment, raceways, and other enclosures to the system grounded conductor, the grounding electrode conductor or both, at the service equipment or at the source of a separately derived system. (NFPA 70)

Grounding Electrode - A Grounding Electrode is a device that establishes an electrical connection to the earth. (NFPA 70)

Grounding Electrode Conductor (Rod) - The Grounding Electrode Conductor (Rod) is the conductor that is used to connect the grounding electrode(s) to the equipment grounding conductor, to the grounded conductor, or to both, at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at the source of a separately derived system. (NFPA 70)

Grounded Effectively - Grounded Effectively refers to intentionally connected to earth through a ground connection or connections of sufficiently low impedance and having sufficient current-carrying capacity to prevent the buildup of voltages that may result in undue hazards to connected equipment or to persons. (NFPA 70)

Battery Negative Connection Point - The Battery Negative Connection Point is the location where negative power connections for DC circuits are connected. This is not to be used for customer connections.

Neutral to Ground Conductor - The Neutral to Ground Conductor is the bond between the generator neutral output and the customer ground connection point.

Protective Bonding Conductor - The Protective Bonding Conductors the protective conductor that is provided for protective equipotential bonding. (IEE Wiring Regulations -17th Edition)

Protective Conductor (PE) - The Protective Conductor is a conductor that is used for some measures of protection against electric shock and intended for connecting together any of the following parts: (IEE Wiring Regulations -17th Edition)

Protective Conductor Current - The Protective Conductor Current is the electric current that appears in a protective conductor, such as leakage current or electric current resulting from an insulation fault. (IEE Wiring Regulations -17th Edition)

Protective Earthing - Protective Earthing pertains to the earth grounding of a point or points in a system, an installation, or in equipment for the purposes of safety. (IEE Wiring Regulations -17th Edition).

Protective Equipotential Bonding - Protective Equipotential Bonding is the grounding of the equipment for the purposes of safety. (IEE Wiring Regulations -17th Edition).

Protective Ground Circuit - Protective Ground Circuit is the grounding of a point or points in a system or in an installation or in equipment for the purposes of safety. Based on IEE definition.