This article is about MGB Installation and commissioning of DC System as per SAIC-T-5119 for Telecommunication Inspectors for Aramco and other international level projects.
What is an MGB and How Does It Help with Installation & Pre-commissioning of DC Systems?
MGB stands for Master Ground Bar and is an essential part of the installation and pre-commissioning of DC systems, as it provides a centralized location for all grounding connections. An MGB is typically a copper bar, and its size and location within the communications equipment room is important for safety and effective grounding of the system. This article explains the importance of an MGB, the minimum size and location requirements, the connection and labeling processes, and the necessary steps for proper installation and pre-commissioning of DC systems.
What is an MGB?
An MGB is a copper bar used to provide a centralized location for all grounding connections in a DC system. It is usually located in the communications equipment room and is typically 6 mm x 102 mm x 500 mm in size. All grounding connections must be made to the MGB using two-hole approved copper terminal lugs.
Where Should an MGB be Located and What is the Minimum Size Requirement?
The MGB should be located as close as possible to the AC service and outside plant main distribution frame, without interfering with cable structures and support. It should also be identified on the building drawings and equipment layout plans, as well as on the bar itself. The minimum size requirement for an MGB is 6 mm x 102 mm x 500 mm.
How Should an MGB Be Connected and Labeled?
The MGB should be bonded to the building ground grid (AC power ground) through two buried leads from opposite sides of the ground grid. The leads should be a minimum of 4/0 AWG (120 mm²) bare tinned-copper conductors and should be installed in PVC conduit. Bends in the ground conductors should be kept to a minimum on all unavoidable bends, with the minimum acceptable bending radius of 300 mm for the installed sizes 4/0 AWG leads.
The MGB should be divided into four zones, namely “P”, “A”, “N” and “I”, and these zones should be permanently labeled on the MGB and on the building drawings. The “P” zone is for surge producers, such as interior radio equipment including cable trays that are connected to radio equipment, Cable Shield/Cable Vault Ground Bar and MDF/Entrance Cable Protector Ground Bar. The “A” zone is for surge absorbers, both ground leads coming from the opposite sides of the ground grid. The “N” zone is for non-isolated equipment, such as DC Power system positive return bus, computer floor, communication racks and cable trays. The “I” zone is for isolated equipment, such as electronic switching equipment & transmission systems and terminal Equipment.
It is important to note that the AC distribution system should not be connected to the building ground grid through the MGB.
Conclusion
An MGB is an essential part of the installation and pre-commissioning of DC systems, as it provides a centralized location for all grounding connections. Proper installation and pre-commissioning of an MGB requires that it meets the minimum size requirements, is located in the appropriate area, is connected to the building ground grid through two buried leads, and is divided into four labeled zones. Following these steps will help to ensure the safety and effective grounding of the DC system.
REFERENCE DOCUMENTS:
SAES-T-795 ” Communication DC Power System