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What MGG Fixed Bus-Bar Supports Are and How to Specify Them

Jun 02 , 2026

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The MGG fixed support type bus-bar support is the standard mechanical anchor for aluminum alloy tubular busbars in power substations. It locks the busbar in place axially, preventing longitudinal movement while transferring mechanical loads to the support structure. For any substation engineer specifying tubular busbar fittings, this is the foundational clamp — not interchangeable with the sliding type, and not optional in a rigid-span layout.

Product Type

MGG Fixed Bus-Bar Support

Applicable Standard

IEC / ANSI / GB

Body Material

Aluminum Alloy (Body & Keepers)

Hardware Material

Hot-Dip Galvanized Steel

Fixed Support Type Functions in Busbar Systems

In a tubular busbar run, not every support plays the same role. The fixed support type — designated MGG — serves as the anchor point that holds the busbar stationary against both vertical loads and horizontal forces along the busbar axis. This is structurally different from a sliding (expansion) support, which allows longitudinal movement to accommodate thermal expansion.

In practice, every busbar span must have at least one fixed support. The remaining supports are typically expansion type (MGS), which permit controlled sliding. This combination allows the busbar to expand and contract with temperature changes — which in outdoor substations can exceed 50 degrees Celsius seasonally — without generating destructive stress at connection points.

The MGG clamps the tubular conductor firmly by compressing keeper plates against the busbar surface. The clamping bolts feature hex-stops, allowing installation with a single wrench. Cap screws are also supplied for upright (vertical post) mounting configurations.

MGG Series Bus-Bar Diameter Coverage

The MGG series spans a wide range of tubular busbar diameters, from 50 mm up to 250 mm outer diameter. Each catalog number encodes the nominal busbar size, and the dimensional parameter C (the mounting bolt circle) can be specified on order when non-standard values are needed. The table below lists the standard MGG catalog numbers with their applicable busbar outer diameters and key dimensions:

Catalog No. Busbar OD (mm) Dimension c (mm) Dimension d (mm) Dimension h (mm)
MGG-50 50 / 54 140 14 80
MGG-60 60 / 54 140 14 90
MGG-80 80 / 72 140 14 98
MGG-100 100 / 90 140 14 114
MGG-130A 130 / 116 190 18 135
MGG-150A 150 / 136 190 18 150
MGG-170A 170 / 156 190 18 170
MGG-200B 200 / 180 225 20 190
MGG-250B 250 / 230 225 20 190
MGG-250D 250 / 230 280 20 190

The suffix letters (A, B, C, D) indicate variants with different mounting bolt circle dimensions (c = 140, 190, 225, 254, 280 mm), allowing the same busbar diameter to be installed on different insulator post heights and support structure geometries.

Material Selection Impact on Substation Service Life

The MGG support uses aluminum alloy for the body and keeper plates, and galvanized steel for the bolts and fasteners. This combination is deliberate.

Aluminum alloy body: Minimizes galvanic corrosion when in direct contact with the aluminum tubular busbar. If a steel clamp grips an aluminum conductor in the presence of moisture, electrolytic action accelerates corrosion of the aluminum. Using the same or a closely matched alloy eliminates this risk. Aluminum also eliminates hysteresis losses that would occur with ferromagnetic steel clamps under AC current.
Hot-dip galvanized steel bolts: Galvanized hardware provides corrosion resistance for the structural fasteners without the weight or cost of full stainless steel, while providing the tensile strength needed to maintain clamping pressure over years of thermal cycling.
Casting production method: The support body is produced by casting, which allows complex geometries and consistent wall thickness. Casting also enables the precise keeper-plate geometry needed for uniform clamping force distribution around the busbar circumference.

Differences Between Fixed, Sliding, and End Supports

The tubular busbar fitting family includes several support types that serve different mechanical functions. Understanding the differences prevents misapplication:

MGG — Fixed Support

Locks busbar against axial movement. Used as the anchor point in each span. Does not allow thermal expansion movement. Typically one per continuous run segment.

MGS — Expansion (Sliding) Support

Allows the busbar to slide axially while providing vertical support. Accommodates thermal expansion and contraction. Used alongside fixed supports to prevent stress buildup.

MGD — End Support

Designed for the terminal ends of a busbar run. Provides end-capping and mechanical termination, often used in conjunction with dead-end fittings.

In outdoor 110 kV and above substations, the typical design practice is to place one MGG fixed support per insulator post group, then specify MGS sliding supports for all intermediate spans. For a 20-meter aluminum tubular busbar run operating in a climate with a 60-degree temperature range, thermal expansion of approximately 1.4 mm per meter would occur (aluminum thermal expansion coefficient of approximately 23 micrometers per meter per degree Celsius), meaning the busbar could expand or contract by roughly 28 mm across its full length. Without sliding supports, this expansion generates stresses that can crack porcelain insulators or deform connection joints.

Field Installation Procedures

The MGG fixed support is designed for straightforward field assembly. The key installation considerations are:

01
Mounting orientation: The support accommodates both horizontal and vertical (upright) mounting. For upright post installations, cap screws supplied with the unit secure the base plate to the insulator cap.
02
Single-wrench clamping: The clamping bolts are fitted with hex-stops, which prevent over-tightening and allow one installer to make up the joint without a backup wrench. This reduces installation error and is especially useful in elevated positions.
03
Positioning sequence: The fixed support should be positioned first in the run, with the busbar fed through or laid into the keeper plates. Sliding supports are then positioned along the remainder of the span before all fasteners are tightened.
04
Dimensional verification: Before ordering, engineers should verify the insulator post hole circle (phi value) and confirm whether the standard C dimension matches or whether a custom phi value must be specified. The manufacturer can accommodate non-standard configurations on request.

Applicable Standards and Certifications

MGG bus-bar supports are manufactured to comply with IEC, ANSI, and GB (Chinese National Standard) requirements for substation fittings. Quality-certified manufacturers hold ISO 9001:2015 for quality management, ISO 14001:2015 for environmental management, and OHSAS 18001 for occupational health and safety.

Test facilities for MGG supports include tensile testing machines rated at 60MT and compression presses rated at 200MT, along with spectrometer analysis for alloy composition verification. Independent test reports from laboratories such as VEIKI-VNL Electric in Hungary and China Electric Power Research Institute are typically available for specification review by procuring utilities.

The HS code for these fittings is 8538900000, which covers parts suitable for use with switchgear and control gear.

Procurement Guidelines and Order Requirements

MGG fixed supports are produced in high-volume casting runs. Typical minimum order quantities from established manufacturers are 20 pieces per size, with FOB pricing in the range of USD 20 to 26 per piece for standard configurations. Production capacity at major Chinese manufacturers exceeds 1,000 pieces per month per product line.

When specifying for a project, the following information should be provided to the manufacturer:

Tubular busbar outer diameter (OD) and wall thickness
Required catalog suffix (A, B, C, or D) based on insulator post geometry
The phi (mounting hole circle) value if different from the standard C dimension
Mounting orientation (horizontal run or upright post)
Applicable installation standard (IEC, ANSI, or GB)
Quantity per size and any phased delivery requirements
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