The GE IS200ISBBG1AAB ISBus Bypass Board is a specialized network interface and fault-tolerant bypass module used within GE Industrial Control Systems. As a member of the ISBB board family, the IS200ISBBG1AAB ISBus Bypass Board is connected between an ISBus full duplex source—either a BAIA module or an ACL module—and the ISBus network itself. Its primary function is to provide the capability to bypass a node of the ISBus when either the power to that node is interrupted or an interlock connection within the full duplex interface is opened. This bypass function is essential for maintaining network continuity and availability in redundant or critical control system architectures, allowing the remaining nodes on the ISBus to continue communicating even when one node is powered down or isolated.
The IS200ISBBG1AAB ISBus Bypass Board is identified by the GE part numbering convention used throughout the Industrial Control Systems product line. The "IS200" prefix identifies the board as a GE Industrial Control Systems product, with "200" specifically indicating that the board is a base-level assembly. The "ISBB" acronym identifies the board's functional designation as an ISBus Bypass Board. The "G1" designation identifies the hardware group and normal coating, while the "AAB" suffix identifies the artwork and functional revision combination. All digits are important when ordering or replacing any board, as boards of different revision levels may not contain identical hardware, and GE ensures backward compatibility of replacement boards while noting that different revision levels may not contain identical components.
The IS200ISBBG1AAB ISBus Bypass Board operates by means of a bypass relay that connects the transmit signals from the full duplex input (P1) to the transmit output data (P2) and receive data input connectors (P3) of the ISBus when 24 V DC is available and the interlock connection on P1 is closed. When the 24 V DC is not supplied to the board, the relay drops out and reconfigures the signal paths so that the receive input is looped back to the transmit output, effectively bypassing the node. The board includes two LED indicators that indicate transmit data input and bypass relay power, providing maintenance personnel with clear visual status information.
This product introduction provides detailed technical information, functional descriptions, connector assignments, configuration guidance, and comprehensive specifications for the GE IS200ISBBG1AAB ISBus Bypass Board, serving as an essential reference for control system engineers, maintenance technicians, and system integrators working with GE industrial control equipment.
Functional Architecture and Signal Processing
The IS200ISBBG1AAB ISBus Bypass Board is built around a robust relay-based bypass architecture that provides deterministic, fail-safe bypass operation without requiring any active electronics in the signal path. This architecture ensures that the bypass function operates reliably even under brownout conditions or total loss of power, making the board suitable for critical control system applications where network continuity must be maintained.
The core of the IS200ISBBG1AAB ISBus Bypass Board is the bypass relay, which is part of the board and performs the signal routing functions. When 24 V DC is available from P1 or P4 and the interlock connection on P1 is closed, the bypass relay is energized and connects the transmit signals from the full duplex input (P1) to the transmit output data (P2) and receive data input connectors (P3) of the ISBus. In this normal operating state, the node is fully connected to the ISBus and can transmit and receive data normally.
When the 24 V DC is not supplied to the IS200ISBBG1AAB ISBus Bypass Board, the bypass relay drops out and the following occurs: the transmit connection between P1 and P2 is interrupted (broken), the receive connection between P3 and P1 is interrupted (broken), and the connection between the receive input (P3) and the transmit output (P2) is made such that RECV DATA IN+ connects to XMIT DATA OUT+ and RECV DATA IN− connects to XMIT DATA OUT−. This loopback configuration effectively removes the failed or isolated node from the ISBus and passes the network signals through to the next node, maintaining the continuity of the ISBus network.
The bypass relay coil pick-up voltage is greater than 14.5 V, and the dropout voltage is 11.0 ± 1.0 V DC during a brownout condition when the 24 V input is decreasing toward zero. The dropout voltage in normal operation is less than 10 V, where normal operation is when the voltage at the relay interlock input is decreasing toward zero while the voltage at the input (P1-7, P1-8) remains at 24 V DC. This dual-threshold behavior ensures that the relay drops out reliably during a brownout and also drops out when the interlock is opened, providing two independent paths for initiating the bypass function.
The bypass relay input voltage is a nominal 24 V DC with a maximum of 30 V DC. The voltage comes into the IS200ISBBG1AAB ISBus Bypass Board on either the full duplex connector P1 or the auxiliary interlock power TB2 through the interlock on the full duplex connector. P1-7 is positive and P1-8 is the return, while TB2-1 is positive and TB2-2 is negative. Neither side of the input voltage is referenced to any other voltage or return on the board, ensuring that the bypass function is isolated from the signal grounds and can operate reliably in the presence of ground potential differences.
Signal Conditioning and Electrical Characteristics
The only transmit and receive signal conditioning performed by the IS200ISBBG1AAB ISBus Bypass Board is the interruption and rerouting of the signals via the bypass relay. This minimal signal conditioning approach ensures that the board introduces negligible signal degradation when the node is connected and provides a clean, low-impedance path when the node is bypassed.
The input signal isolation of the IS200ISBBG1AAB ISBus Bypass Board is greater than 1 megohm at 500 V RMS for 1 second, providing excellent isolation between the ISBus signals and the relay control circuitry. This isolation is important for maintaining signal integrity and for protecting the board from ground potential differences and common-mode voltages that may be present on the ISBus network.
Input termination is not done on the IS200ISBBG1AAB ISBus Bypass Board. The receiver circuitry is capable of driving a transformer-coupled output load with a 100 ohm (±10%) resistive termination on its secondary, and the receiver output does not present any differential DC levels on its output. The receiver output terminals are terminated with 100 ohm resistors, and the contact current rating is greater than 200 mA at 10 V RMS with isolation of at least 40 dB at 1 MHz. The maximum operating power for one or multiple relays is less than 1 W, ensuring that the board has a low power consumption and generates minimal heat.
Connector Assignments and Interfaces
The IS200ISBBG1AAB ISBus Bypass Board provides a comprehensive set of connectors that interface with the full duplex source, the ISBus network, the auxiliary interlock power, and the interlock bypass jumper. Each connector serves a specific function in the overall signal chain, and understanding these connector assignments is essential for installation, maintenance, and troubleshooting.
The P1 connector is the full duplex connector that connects the board to the ISBus full duplex source, either a BAIA module or an ACL module. Table 5-1 describes the P1 connector pin assignments: pin 1 is XMIT DATA IN+ (positive RS-422 input), pin 2 is XMIT DATA IN− (negative RS-422 input), pin 3 is RECV DATA OUT+ (positive RS-422 output), pin 4 is RELAY INTERLOCK (routing of the 24 V DC to the full duplex source), pin 5 is RELAY INTERLOCK RTN (routing of the 24 V DC back from the full duplex source to energize the relay or relays), pin 6 is RECV DATA OUT− (negative RS-422 output), pin 7 is INTERLOCK 24VDC (24 V DC input), and pin 8 is INTERLOCK 24VDC RTN (24 V DC return input).
The P2 connector is the transmit data connector that connects the board to the ISBus transmit path. Table 5-2 describes the P2 connector pin assignments: pins 1 and 2 are not connected, pin 3 is XMIT DATA OUT+ (the transmitter positive output to the ISBus +), pins 4 and 5 are not connected, pin 6 is XMIT DATA OUT− (the transmitter negative output to the ISBus −), and pins 7 and 8 are not connected.
The P3 connector is the receive data connector that connects the board to the ISBus receive path. Table 5-3 describes the P3 connector pin assignments: pins 1 and 2 are not connected, pin 3 is RECV DATA IN+ (the receiver positive input from the ISBus +), pins 4 and 5 are not connected, pin 6 is RECV DATA IN− (the receiver negative input from the ISBus −), and pins 7 and 8 are not connected.
The TB2 connector is the auxiliary interlock power terminal board that provides an alternative path for the 24 V DC interlock power. Table 5-4 describes the TB2 connector pin assignments: pin 1 is AUX INTERLOCK 24VDC (24 V DC from an auxiliary or external power source) and pin 2 is AUX INTERLOCK 24VDC RTN (24 V DC return from the auxiliary or external power source).
The JP1 connector is the interlock bypass jumper that allows the interlock to be shorted out for testing or special operating conditions. Table 5-5 describes the JP1 jumper positions: position 1-2 is the default position, which means the module must have the external interlock closed to energize the relay or relays; position 2-3 places a jumper between these pins to short out the interlock, although power will still have to be applied to the board either via P1-7,8 or P5-1,2 to energize the relay or relays.
Application Suitability and System Integration
The IS200ISBBG1AAB ISBus Bypass Board is an essential component in GE Industrial Control Systems that use the ISBus network for communication between control nodes. Its ability to automatically bypass a failed or isolated node ensures that the remaining nodes can continue communicating, maintaining the availability and reliability of the control system even in the event of a node failure or power loss.
The IS200ISBBG1AAB ISBus Bypass Board is typically installed between an ISBus full duplex source, such as a BAIA module or an ACL module, and the ISBus network. When the source is powered and the interlock is closed, the bypass relay is energized and the source is fully connected to the ISBus, allowing normal communication. If the source loses power or the interlock is opened, the bypass relay drops out and the source is automatically bypassed, with the receive input looped back to the transmit output so that the network signals pass through to the next node.
The board's dual dropout thresholds—11.0 ± 1.0 V DC during a brownout and less than 10 V when the interlock is opened—ensure that the bypass function operates reliably under both power failure and interlock opening conditions. The board's minimal signal conditioning approach, with only relay-based interruption and rerouting, ensures that the ISBus signals are not degraded when the node is connected and that the bypass path is clean and low-impedance when the node is bypassed.
The JP1 interlock bypass jumper provides flexibility for testing and special operating conditions, allowing the interlock to be shorted out when necessary while still requiring power to be applied to the board to energize the relay. This feature is useful during commissioning and maintenance, when the interlock may need to be bypassed temporarily to allow testing of the node.
Maintenance and Lifecycle
The IS200ISBBG1AAB ISBus Bypass Board is designed for long service life with minimal maintenance. The board contains one relay as its only moving part, and its solid-state signal path and minimal component count ensure high reliability in continuous industrial operation. Routine maintenance consists of periodic visual inspection of the board, connectors, and LED indicators, and verification that the bypass relay is operating correctly by checking the LED indications and, if necessary, testing the bypass function during a scheduled outage.
The two LED indicators on the IS200ISBBG1AAB ISBus Bypass Board provide clear visual indication of the transmit data input and the bypass relay power status. If the bypass relay power LED is off when it should be on, the maintenance technician should check the 24 V DC input at P1-7, P1-8 or TB2-1, TB2-2, and verify that the interlock on P1 is closed or that the JP1 jumper is properly configured. If the transmit data input LED is off when it should be on, the technician should check the full duplex source and the P1 connection.
If the board requires replacement, the process is straightforward. After de-energizing the associated equipment and verifying that no power exists, the connectors should be labeled and disconnected, and the board should be removed from its mounting. The replacement board should be installed in the same position, the connectors reconnected as labeled, and the bypass function verified before returning the system to service.
GE Industrial Control Systems ensures compatibility of its replacement boards, even though boards of different revision levels may not contain identical hardware. When ordering a replacement IS200ISBBG1AAB ISBus Bypass Board, provide the complete part number and description, the drive or system serial number, and the Material List (ML) number. The factory may substitute later versions based on availability and design enhancements, but backward compatibility of replacement boards is guaranteed.
Conclusion
The GE IS200ISBBG1AAB ISBus Bypass Board is a reliable, robust, and essential network interface module for GE Industrial Control Systems that use the ISBus network. Its relay-based bypass architecture, dual dropout thresholds, minimal signal conditioning, and clear LED indicators provide automatic and reliable bypass of failed or isolated nodes, ensuring that the remaining nodes can continue communicating and that the control system maintains high availability.
With its comprehensive connector set, configurable interlock bypass jumper, and clearly marked LED indicators, the IS200ISBBG1AAB ISBus Bypass Board is designed for easy installation, verification, and maintenance. Backed by GE's quality manufacturing, global support network, and commitment to backward compatibility, the IS200ISBBG1AAB ISBus Bypass Board continues to deliver the performance, durability, and reliability that industrial users expect from GE. Whether used in a new installation or as a replacement for an existing board, the IS200ISBBG1AAB ISBus Bypass Board provides the network bypass functionality required for reliable and efficient control system operation.
