How to Select the Jaw Opening of a Portable Grounding Device? How Can Buyers Match It to Actual Connection Points?

When purchasing portable grounding and short-circuiting devices, clamps often feature specifications such as:

• Maximum jaw opening: 20 mm
• Maximum jaw opening: 50 mm
• Maximum jaw opening: 75 mm

Many buyers, upon seeing these numbers, will directly compare them to the dimensions of the connection points:

The conductor diameter is less than 50 mm, so a 50 mm clamp can be used.

This assessment is insufficient.

The jaw opening is only one dimensional parameter in matching a clamp to a field connection point. To select a truly reliable clamp, you must also verify the following:

• Minimum clamping range
• Maximum clamping range
• Connection point shape
• Round conductor diameter
• Busbar thickness
• Jaw shape
• Contact surface structure
• On-site access space
• Operating direction
• Whether operated via an insulated operating rod
• Short-circuit current capacity
• Technical evidence for the entire portable grounding system

Therefore, when handling portable grounding system projects, we do not simply ask the customer:

What clamping size is required?

We focus more on:

Where the clamp needs to be connected, what the actual geometric dimensions of that location are, how the clamp is accessed and operated, and whether the final clamp still meets the short-circuit current requirements for the entire system.

A more reasonable selection logic is:

Connection point → Geometric shape → Actual dimensions → Clamping range → Clamp structure → On-site space → Operating method → Electrical capacity → Final clamp model

Quick conclusion: Maximum clamp opening is just one parameter

When selecting a portable grounding clamp, at least three levels of evaluation must be completed.

First Level: Do the Dimensions Match?

Do the clamp’s minimum and maximum clamping ranges cover the on-site connection points?

Second Level: Does the Geometric Shape Match?

Connection points include:

• Round conductors
• Flat busbars
• tubular busbar
• grounding busbar
• fixed grounding point
• ball-type grounding point

Different shapes typically require different clamp designs.

Third Level: Technical Capability Match

Even if the fixture can mechanically grip the connection point, the following must still be verified:

• Fixture short-circuit current capacity
• Conductor cross-sectional area
• Connection terminals
• Complete configuration
• Related Test Evidence

Therefore, keep these three principles in mind:

Maximum jaw opening ≠ Full clamping range

Dimensional match ≠ Geometric match

Mechanically capable of clamping ≠ Electrically compliant

What is the difference between jaw opening and clamping range?

These two parameters are often confused.

Maximum jaw opening

refers to the maximum dimension the fixture is structurally capable of opening.

For example:

Maximum jaw opening: 50 mm

This only tells you:

The jaws can open to a maximum of approximately 50 mm.

But it does not tell you:

Whether 5 mm, 10 mm, 20 mm, or 30 mm are all suitable.

Minimum clamping range

Some clamps have a clearly defined minimum applicable size.

For example, a wide-opening gripper might be suitable for:

40–75 mm

rather than:

0–75 mm.

Therefore, if the connection point on-site is only 10 mm thick, a gripper with a maximum opening of 75 mm may not necessarily be suitable.

Effective Clamping Range

What you should really focus on when purchasing is:

the effective range between the minimum and maximum applicable sizes.

Therefore, we recommend that procurement documents not simply state:

Maximum jaw opening ≥50 mm

but instead require suppliers to provide:

• Minimum clamping range
• Maximum clamping range
• Applicable joint types
• Corresponding jaw configuration

Why is “the wider the opening, the more versatile” a flawed procurement logic?

A larger jaw opening does not automatically mean better versatility.

Large clamps may also have:

• larger clamp body volume
• greater weight
• greater space requirements for operation
• different minimum clamping ranges
• different jaw profiles
• different operating mechanisms

Inside the confined space of a switchgear cabinet, a large clamp that theoretically can grip an 80 mm conductor may be unable to access the connection point due to its excessive size.

Therefore, the goal of selection should not be:

Finding the largest opening.

But rather:

Finding a suitable clamp that can reliably accommodate the actual dimensions and geometry of the connection point.

Step 1: First, identify the connection point

Clamp selection should start with the actual connection point on-site, not with a supplier’s catalog.

Common connection points include:

• Round conductors
• Flat busbars
• Tubular busbars
• Grounding bars
• Grounding studs
• Ball-head grounding points
• Specialized grounding connectors
• Structural grounding points

Different connection points have completely different requirements for clamps.

What dimensions should be provided for round conductors?

If the connection involves a round conductor, the purchaser typically needs to provide:

Conductor outer diameter

For example:

Round conductor diameter: 28 mm

The supplier then needs to confirm:

• Minimum clamping diameter
• Maximum clamping diameter
• Jaw profile
• Contact surface type
• Compatibility with the conductor material
• On-site operation method

Do not simply tell the supplier:

185 mm² conductor.

Conductor cross-sectional area and actual outer diameter are not exactly the same procurement parameters.

Mechanical matching of the clamp more directly requires:

Actual outer diameter.

For flat busbars, simply providing the “width” is insufficient.

This is a very common issue in inquiries for portable grounding clamps.

For example, a customer might tell us:

Busbar width = 100 mm

But this is not sufficient to determine the clamp.

A standard busbar dimension should be closer to:

100 × 10 mm

This means:

• Width = 100 mm
• Thickness = 10 mm

If the clamp actually grips 10 mm of the busbar’s thickness from the edge, then the actual dimension entering the clamp’s jaws is likely to be:

10 mm

rather than 100 mm.

Therefore, for flat busbars, we typically ask customers to provide:

Width × Thickness

and further specify:

the direction from which the clamp is expected to enter.

This is much more useful than simply providing “100 mm busbar.”

Do not confuse busbar width with busbar thickness.

Suppose a project involves:

an 80 × 10 mm copper busbar

A clamp with a maximum jaw opening of 20 mm might, based on dimensions alone, be able to cover a 10 mm thickness.

However, this does not guarantee a proper fit.

You must also confirm:

• Whether the jaws fit the flat surface
• The direction of contact
• Whether there is space behind the busbar
• Whether there are insulating spacers
• Whether the clamp body can fit into
• Whether the operating mechanism can rotate

Therefore:

The actual dimensions that fit into the clamp opening are more important than the nominal width of the busbar.

For tubular busbars, consider both the diameter and the shape of the clamping jaws

If the on-site connection point is a tubular busbar or other round tube structure, the following information should be provided:

• Outer diameter
• Material
• Surface condition
• Permissible contact area
• On-site entry direction

A clamp with a maximum jaw opening of 40 mm—even if the jaws are designed for flat busbars—does not necessarily mean it will fit a tubular busbar with a diameter of 35 mm.

It is important to remember:

Just because a dimension fits within the jaw opening does not mean the jaw profile will match correctly.

Ball studs and dedicated grounding points cannot be evaluated using standard jaw opening logic

Some substations and switchgear use specialized components such as:

• Ball Stud
• Earthing Ball
• Fixed Earthing Point
• Dedicated Grounding Interface

For these types of interfaces, what truly needs to be matched is:

the specific connection geometry.

Purchasers should not select standard clamps based on the assumption that:

the larger the maximum jaw opening, the better.

In such scenarios, the approach should typically be:

Interface type → Dedicated clamp → Operating method → Full rated capacity

Step 2: Measure the actual dimensions of the area to be gripped by the jaws

When purchasers provide dimensions, the most important question is not:

How large is the device as a whole?

but rather:

How large is the specific area that the fixture actually needs to grip?

It is recommended to provide the following based on the connection point:

Round Conductor

Provide:

Outer Diameter

Flat Busbar

Provide:

Width × Thickness

and specify the clamping direction.

Tubular Busbar

Provide:

Outer Diameter

Fixed connection points

Provide:

• Connection diameter
• Thickness
• Stud size
• Ball joint specifications

Depending on the actual structure.

If the on-site structure is complex, we prefer that customers also provide:

Dimensional drawings + clear photos

rather than just photos.

Why are photos alone usually insufficient?

Photos help us determine:

• Connection point shape
• Surrounding space
• Operating direction
• Obstacles
• Adjacent equipment

However, it is difficult to reliably determine the following from photos:

• Specific diameter
• Busbar thickness
• Spacing
• Rear clearance
• Rotation space for the clamp

Therefore, when JINPOWER processes inquiries for grounding clamps, if the clamp selection clearly depends on dimensions, we typically recommend that customers also provide:

• On-site photos
• Dimensions
• Simple sketches
• Equipment drawings

This significantly reduces the risk of selecting the wrong clamp.

Step 3: Check Both the Minimum and Maximum Clamping Ranges

Don’t just look at the largest number in the catalog.

For example:

Maximum Jaw Opening = 75 mm

The buyer should also ask:

What is the Minimum Clamping Range?

This is because different models with the same maximum jaw opening may have completely different minimum applicable sizes.

Therefore, the RFQ can directly specify:

• Minimum Clamping Range
• Maximum Clamping Range
• Applicable Conductor Range
• Applicable Busbar Range

This is more reliable than simply requiring:

Jaw Opening ≥75 mm

is more reliable.

Why might two clamps still be different even with the same Maximum Opening?

Because the Maximum Opening only describes a geometric boundary.

Even if two clamps both have:

75 mm maximum opening

they may still differ completely in the following aspects:

• Minimum Range
• Jaw Shape
• Jaw Surface
• Contact Area
• Pivot Structure
• Operating Mechanism
• Clamp Body Size
• Fault Rating
• Cable Connection

Therefore:

Do not use a single “Maximum Opening” parameter as a substitute for a complete model review.

Step 4: Match Jaw Geometry and Contact Face

Once the jaw dimensions are correct, the next step is to determine:

Are the jaws designed for this connection point?

Common configurations may include:

• C-clamp
• Flat-face clamp
• Omni-directional clamp
• Duckbill clamp
• Tower clamp
• Special-purpose ball-joint clamp

Not only do they have different openings, but their jaw shapes and contact methods also vary.

Flat Connection Points

You need to confirm whether the jaws are suitable for flat contact.

Circular Conductors

You need to confirm whether the jaw profile is suitable for a circular surface.

Special Structures

A specialized interface may be required.

Therefore:

Jaw Shape should be approved in conjunction with Connection Geometry.

If you need to first determine the general category of the clamp and then further confirm the dimensions, you can refer to the clamp classification page for portable grounding devices during the review process.

Smooth Jaw and Serrated Jaw cannot be determined based on their names alone.

Different clamps may feature:

• Smooth Contact Face
• Serrated Contact Face
• Special Profile

These designs are related to:

• Connection point material
• Surface condition
• Clamp application
• Manufacturer’s design

Purchasers are advised against relying on generalizations such as:

“Serrated always provides better contact”

or:

“Smooth is always safer”

The specific product design and technical evidence should be reviewed.

Step 5: Inspect the Clamp Body, Not Just the Jaw

This is particularly important for switchgear and space-constrained equipment.

Assumption:

Busbar Thickness = 20 mm
Clamp Maximum Opening = 40 mm

Based on the dimensions, this appears to be a perfect fit.

However, the actual installation site may only have:

very limited lateral space.

In this case, it is necessary to check not only the Jaw Opening, but also:

• Clamp Body Width
• Handle
• Eye Screw
• Pivot
• Cable Connection
• Operating Head

Therefore:

Just because the jaw can grip the busbar does not mean the entire clamp will fit into the equipment space.

This is why it is best to provide the following for switchgear projects:

• Compartment Drawing
• Connection Point Photo
• Clearance Dimension

Step 6: Confirm Access Direction

Even with the same busbar dimensions, completely different clamps may be required depending on the specific on-site location.

The following must be confirmed:

• Top entry
• Side entry
• Front entry
• Entry at a restricted angle

For example, a 10 mm-thick flat busbar should, in theory, easily fit within the clamp’s range.

However, if:

• the back is flush against an insulated structure
• space on both sides is limited
• there is a partition in front

the clamp may not actually reach the connection point correctly.

Therefore, when reviewing clamps, we confirm:

Dimensions

and

On-site access direction

separately.

Step 7: Confirm how the clamp is operated

Portable grounding clamps may use different operating methods, such as:

• Manual operation
• Operation via insulated operating rod
• Ring-shaped operating interface
• Structure permanently mounted on the operating pole
• Dedicated connector

Therefore, even after confirming the correct jaw opening, we must also ask:

Can this clamp be used under the project’s specified operating method?

If the project requires the clamp to be operated using an insulated operating pole, we must also confirm:

• Clamp Operating Interface
• Pole Head
• Adapter
• Pole Length
• Complete Connection Method

The following situation must not occur:

The clamp dimensions are completely correct, but there is no way to connect it to the on-site insulated operating pole.

Step 8: After mechanical compatibility is confirmed, check the Fault-Duty Evidence

This is a very important technical requirement.

Consider a clamp:

• It can grip the busbar
• The opening range is correct
• The jaw shape is correct
• There is also sufficient on-site space

It still cannot be approved directly.

The following must also be checked:

• Rated Current
• Rated Time
• Peak Factor
• Clamp Test Evidence
• Cable Cross-Section
• Ferrule
• Complete Assembly Configuration

The logic behind portable earthing and short-circuit devices as defined in IEC 61230 is, by its very nature, more than just a mechanical clamping issue.

For a complete Fault Duty review, please refer to our Procurement Guide for Fault-Current Ratings of Portable Earthing Devices.

Jaw Opening Does Not Determine Fault-Current Rating

This is a very common misconception.

Do not assume that:

The larger the jaw opening, the higher the fault-current capacity.

There is no such direct correlation between the two.

Fault-current capacity is also influenced by:

• Clamp Material
• Clamp Construction
• Contact System
• Cable Connection
• Ferrule
• Conductor
• Complete Assembly

and other factors.

Therefore, during the procurement approval process, these two issues should be considered separately:

Mechanical Interface Review

Can it clamp correctly?

Electrical Capability Review

Can it withstand the project-specified fault duty?

Only when both issues are approved is the clamp truly suitable for the project.

Clamp Interface Selection Matrix

This table is more suitable for a formal RFQ than simply writing:

Jaw Opening ≥50 mm

How should clamp requirements be described in an RFQ?

If the purchaser already has the on-site dimensions, the RFQ can be written in greater detail.

For example:

Connection Point: Flat copper busbar
Busbar Size: 80 × 10 mm
Clamp Direction: Clamping in the 10 mm thickness direction
Site Access: Side access
Operating Method: Insulated operating rod
Fault Duty: As per the project’s Technical Specification
Supplier to confirm: Clamp Model, Minimum/Maximum Clamping Range, Jaw Geometry, Operating Interface, and Supporting Evidence.

An RFQ like this is more likely to yield the correct solution than:

Need grounding clamp, 50 mm jaw

Don’t forget the interface between the clamp and the cable

The focus of this article is:

Clamp → Site Connection Point

However, the complete current path also includes:

Cable → Ferrule → Clamp → Connection Point

Therefore, after selecting the clamp, you must also confirm:

• Ferrule
• Cable Cross-Section
• Clamp Cable Connection
• Termination
• Assembly Evidence

For this aspect, please refer to our Grounding Cable Termination, Ferrule, Lug, and Clamp Connection Review Guide.

The final clamp model should be finalized during the drawing phase

After completing the connection point review, the final clamp model should not exist solely in the quotation.

For project-based portable earthing sets, we strongly recommend specifying the following in the production drawing:

• Clamp Model
• Quantity
• Connection Point
• Jaw Range
• Cable
• Ferrule
• Cluster
• Operating Pole Interface

This ensures the following process:

Site Interface → Clamp Selection → Production Drawing → BOM → Manufacturing → FAT

For pre-production drawing reviews, please refer to our Portable Earthing Set Drawing Approval Checklist.

Common Procurement Mistakes

Providing only the Maximum Jaw Opening

Without knowing the Minimum Range, it is still impossible to determine the full applicable range.

Assuming that everything from 0 to the Maximum can be clamped

Large-opening clamps may have a clearly defined minimum clamping range.

Providing only the Busbar Width

Both the Thickness and the actual clamping direction should be provided.

Selecting Flat Busbar Clamps Based on Round Conductor Logic

Diameter and Busbar Thickness are different interface specifications.

Assuming a Large Enough Opening Means the Jaw Shape Is Suitable

Dimensions and shape are two separate considerations.

Assuming that a larger clamp is more versatile

A larger clamp may actually be unable to fit into narrow equipment.

Ignoring the minimum clamping range

This is a very common omission in specifications.

Ignoring the clamp body dimensions

The jaws may fit, but the clamp body may not.

Ignoring the Access Direction

On-site conditions may only allow access from one direction.

Ignoring the Operating Pole Interface

The clamp may be correct, but it cannot be operated according to on-site regulations.

Providing Only Photos, Not Dimensions

Photos can illustrate the structure but cannot replace diameter and thickness specifications.

Fault Duty is no longer checked after jaw matching

Mechanical matching is only part of the selection process.

Checking only the clamp rating, not the complete assembly

Portable grounding devices should be reviewed as a complete system.

Interpreting “Universal Clamp” as requiring no dimensions

“Universal” still has:

• Minimum Range
• Maximum Range
• Geometry
• Rating
• Access Requirement

How do we review a quotation request for a Grounding Clamp interface?

When JINPOWER handles Portable Earthing Set projects, we typically do not start with:

What is the Jaw Opening?

Our review sequence more closely follows the process below.

We first confirm the Connection Point

We need to know:

• Round Conductor
• Flat Busbar
• Tubular Busbar
• Earth Point
• Ball Stud
• Dedicated Interface

Different connection points correspond to different Clamp Families.

We confirm the Actual Dimensions

For example:

• Diameter
• Width × Thickness
• Stud Size
• Ball Size

Avoid guessing dimensions based solely on product names.

We confirm the actual clamping direction

This is especially important for flat busbars.

For a 100 × 10 mm busbar, whether it is clamped from:

• Clamped in the 10 mm direction
• Approached from the 100 mm direction
• Connected at other specific locations

This directly affects clamp selection.

We compare the minimum and maximum ranges

We do not rely solely on the maximum jaw opening.

We Review Jaw Geometry

Ensure the jaw geometry matches the actual connection point.

We Inspect On-Site Space

For switchgear and panel projects, we pay special attention to:

• Clearance
• Barrier
• Access Angle
• Clamp Body

We verify the operating method

If an insulated operating handle is required, we also verify:

• Clamp Interface
• Pole Head
• Adapter

We then review the Fault Duty

Including:

• Rated Current
• Rated Time
• Peak Factor
• Cable Size
• Supporting Evidence

Finally, include the clamp in the Production Drawing and BOM

This ensures that the final product is not:

a “similar 50 mm clamp”

but rather:

a specific model and complete configuration that has been approved for the project.

Our goal is not to recommend the clamp with the widest opening to the customer, but to find:

a clamp that is truly suitable for the actual connection point, on-site space, operating method, and Fault Duty.

FAQ

How much larger should the jaw opening be than the conductor diameter?

You cannot use a fixed safety margin that applies to all clamps. You should check the specific model’s minimum/maximum clamping range and the manufacturer’s requirements, rather than adding a uniform safety margin to the maximum opening on your own.

Does a 50 mm jaw opening mean it can clamp 0–50 mm?

Not necessarily. You must also verify the minimum clamping range.

What jaw opening should be selected for a 100 × 10 mm busbar?

You cannot rely solely on the 100 mm dimension. First, confirm the actual direction from which the clamp will grip. If the clamp is connecting a 10 mm-thick component, you must further verify the jaw geometry, access space, and specific product range.

Is a larger jaw opening always better?

No. A clamp that is too large may result in issues such as a mismatch with the minimum clamping range, excessive bulk, increased weight, or insufficient space on-site.

Can the same clamp be used for round conductors and flat busbars?

Some clamps may support multiple interfaces, but this cannot be assumed. You should check the specific jaw geometry and the manufacturer’s defined scope of application.

Can a clamp be verified based on photos alone?

Photos are helpful, but if the interface fit depends on specific dimensions, it is recommended to provide both the dimensions and a drawing.

If the clamp can secure the connection, is it still necessary to check the fault rating?

Yes. Mechanical fit and electrical qualification are two separate checks.

Can a universal grounding clamp be used on all connection points?

No. Even if labeled “universal,” there are still limitations regarding applicable sizes, shapes, operating methods, and fault ratings.

Practical Buyer Summary

Clamp selection for a Portable Earthing Set should not begin solely with:

Maximum Jaw Opening

A more reliable selection sequence is:

Connection Point

↓

Geometry

↓

Actual Dimension

↓

Minimum / Maximum Clamping Range

↓

Jaw Shape

↓

Contact Face

↓

Available Access

↓

Operating Method

↓

Fault-Duty Evidence

↓

Approved Clamp Model

Buyers should keep the following three key conclusions in mind:

The Maximum Jaw Opening does not represent the complete clamping range.

A correct jaw size does not necessarily mean the jaw geometry is correct.

A correct mechanical interface does not necessarily mean the clamp meets the project’s fault-duty requirements.

If the project is procuring complete Portable Earthing and Short-Circuiting Kits, it is recommended to provide the following during the RFQ phase:

• Connection Type
• Diameter or Width × Thickness
• Access Direction
• Operating Method
• Fault Duty
• Drawing / Photo

This allows suppliers to select clamps based on the project’s interface specifications, rather than guessing model numbers from a catalog.

Once the clamp selection is complete, finalize the configuration using production drawings, the BOM, and supporting evidence.

This establishes:

Site Connection Point → Clamp → Ferrule → Cable → Complete Earthing Set → Test Evidence

a complete procurement evidence chain.