The issue is grounding.
When a sheet metal part or assembly will house or support electrical components, it’s important to consider grounding requirements as early as possible. Grounding features are relatively simple and inexpensive to add before fabrication. However, failing to think through the complete grounding path in advance can lead to redesign, secondary operations, coating rework, additional hardware, field troubleshooting, and schedule delays.
What Grounding and Bonding Mean for Sheet Metal Assemblies
At its most basic level, bonding joins conductive metal sections to establish electrical continuity throughout the entire assembly. Grounding then connects the resulting conductive assembly to the designated grounding system. Although much of the physical sheet metal work discussed in this article is technically bonding, we’re using grounding as the familiar umbrella term throughout.
Sheet metal is not normally intended to carry current, but an enclosure, door, panel, or chassis(opens in new tab) can become energized during a fault. The grounding and bonding system provides a deliberate path for that fault current to return to the electrical supply source, allowing a breaker, fuse, or other protective device to operate.
When this path is missing or incomplete, it can increase the risk of electrical shock, equipment damage, overheating, or fire. An inconsistent path can also contribute to electrical noise, electromagnetic interference (EMI)(opens in new tab), communication problems, and unreliable equipment operation.
A marginal connection may perform as expected during initial testing and then become intermittent after installation. Movement, vibration, corrosion, insulating coatings, and repeated servicing can further degrade the connection, turning it into a difficult and expensive field problem.
Common Grounding Features for Sheet Metal Parts
The right grounding feature depends on the connection location and how the assembly will be used. A permanent connection on a fixed enclosure wall has different requirements from a bond across an access door that opens daily. In either case, the goal is a consistent electrical connection that meets the product’s requirements and remains reliable throughout its service life.
Connections on Fixed Components
Threaded studs provide a defined attachment point for a ring terminal, lug, or grounding conductor. Depending on the design, this may be a self-clinching stud(opens in new tab), including specified PEM® hardware, or a weld stud.
Self-clinching hardware can work well in relatively thin sheet metal, provided the selected fastener matches the material’s hardness and thickness. When welding better suits the material, geometry, appearance, or finishing requirements, a weld stud may be the more appropriate choice.
Other designs use a dedicated grounding lug or terminal that remains accessible during installation and service. A dedicated hole with a specified bolt, screw, washer, and terminal stack may also provide the required connection. In that case, the drawing should define the complete hardware stack rather than leaving the assembler to determine what goes into the hole.
Connections Across Doors and Removable Panels
Doors, covers, and removable access panels present a different challenge because the connection must tolerate movement or disassembly. Hinges and ordinary mechanical fasteners don’t always provide consistent electrical continuity, especially after the components have been painted or powder coated.
Flexible bonding straps and grounding jumpers create a deliberate electrical path between the moving component and the main structure. This path prevents the connection from depending entirely on incidental contact through a hinge or fastener. A conductive hinge may also be appropriate when it’s specifically designed and qualified for that purpose, but an ordinary painted hinge should not be assumed to remain conductive.
Strap placement and routing also matter. The door should open fully without the strap binding, snagging, interfering with service access, or flexing so sharply that it wears prematurely.
How to Choose the Right Grounding Feature
No single grounding feature is right for every assembly. The appropriate choice depends on:
- What the connection must accomplish electrically and which standards apply
- Whether the connection will remain fixed or must tolerate movement, removal, or repeated servicing
- Whether the hardware is compatible with the sheet material, hardness, and thickness
- Whether the feature can be installed and accessed within the available space and planned assembly sequence
- How finishing, environmental exposure, and corrosion could affect the connection over time
Once the grounding feature is selected, the designer must then map the complete path, preserve the required contact surfaces, and make sure every feature can be fabricated and assembled as intended.
Best Practices for a Reliable Grounding Path
Grounding locations, finishes, and hardware installation all affect one another. A connection that works in the CAD model must remain intact after fabrication, finishing, assembly, and service.
1. Map the Complete Path Early
Before placing any grounding hardware, the product designer or electrical engineer must define the grounding and bonding strategy. That process identifies the primary grounding point and determines which conductive sections must connect to it. It also specifies any continuity or resistance requirements and defines how they will be verified.
Those requirements may come from the National Electrical Code(opens in new tab), a UL or IEC standard, a military specification, or a customer-specific engineering requirement. Which requirements apply will depend on the product’s intended use and market. A sheet metal fabricator can confirm whether the specified features are manufacturable, but the customer remains responsible for defining the electrical requirements and verifying the completed product’s compliance.
With those requirements established, grounding points should be placed intentionally:
- Choose locations that support the shortest, most direct practical path identified by the electrical design.
- Position grounding points near the components or circuits they serve when practical.
- Use multiple grounding or bonding points when required for larger or multi-section assemblies.
- Account for cable routing, terminal orientation, nearby bends and hardware, tool clearance, assembly order, door movement, and future service access.
Finally, look beyond each individual connection to the complete assembly. Inventory the enclosure body, back panel, internal partitions, doors, covers, and removable access panels. Starting with each conductive section, trace the intended path back to the primary grounding point.
Pay particular attention to seams, removable covers, overlapping flanges, bolted or welded joints, doors, and hinges. Any of these interfaces can interrupt the path. If continuity depends on paint being scratched, an ordinary hinge remaining conductive, or an unspecified fastener making contact, the connection is not sufficiently defined.
2. Design Around Finishes and Contact Surfaces
While powder coating, wet paint, and anodizing protect the part, they can also interfere with the metal-to-metal contact that grounding depends on. Anodizing is generally resistive, while powder coating is generally insulating. Chromate conversion coating(opens in new tab), on the other hand, is often better suited to conductive contact and bonding applications. The best finish depends on the base material, required electrical performance, environment, and application.
Whatever finish is selected, the designer must consider both its electrical properties and its physical buildup. Powder coating, for instance, typically adds about 0.003 to 0.004 inches of buildup(opens in new tab), though the exact amount varies by powder and specification. That added material can reduce the finished diameter of holes, interfere with threads, change mating fits, or prevent two surfaces from making the contact the grounding design requires.
Because the selected finish can affect both part dimensions and metal-to-metal contact, plan the finish and grounding requirements together. Designers can preserve electrical contact by specifying masked or no-finish areas around grounding studs, bare contact pads beneath lugs, clean threads, and uncoated mating surfaces. At Approved Sheet Metal, we may use heat-resistant silicone plugs for internal threads and high-temperature tape to protect external threads and other specified areas during finishing.
3. Coordinate the Hardware With the Manufacturing Sequence
Once you’ve mapped the path and accounted for the finish, make sure the selected hardware is compatible with the sheet and the planned manufacturing sequence. Every self-clinching fastener requires a manufacturer-specified mounting-hole diameter and tolerance(opens in new tab), and even fasteners with the same thread size can require different holes. The drawing should therefore identify the exact manufacturer and part number, along with the correct shank code(opens in new tab), sheet material, thickness, hardness, and minimum edge distance. If any of these details are wrong, the hardware may not seat properly, the panel may deform, or the fastener may spin or loosen. At ASM, incorrect hardware hole sizes are the number one issue we address before sending parts to the fabrication floor.
Placement must also work with the fabrication process. Hardware located too close to a bend can interfere with press brake tooling or distort during forming and insertion. It may also be impossible to install if it sits deep inside an enclosure, near a return bend, or beyond the insertion press’s reach.
Finally, determine whether to install the hardware before or after finishing. ASM generally recommends adding hardware after powder coating, although the correct sequence depends on the component and application. Installing it before coating may require masking the threads, hardware head, and conductive contact area, while installing it afterward can risk damaging the finish. When the hardware is part of the grounding path, either approach must preserve the required metal-to-metal contact.
What to Include in Your Sheet Metal Design Package
Once you’ve worked through the grounding design and made decisions about the material, hardware, finish, and grounding path, it’s time to package that information for your fabricator. The goal is to remove guesswork by clearly identifying every grounding and bonding location and showing how those connections work within the complete assembly.
The drawing package should define the hardware, finish exclusions, installation sequence, and any electrical testing or documentation requirements. Along with fully dimensioned part drawings(opens in new tab), include the 3D model and any assembly drawings, wiring diagrams, or component details needed to show how doors, covers, panels, and related parts fit together. If several fabricated parts make up the enclosure, submit them together so the contact surfaces and interfaces can be reviewed in context.
Use the following checklist to confirm that the necessary information is in place before releasing the design package.
Grounding and Bonding Design Checklist
| Design practice | What to specify or provide | Why it matters |
|---|---|---|
| Define the complete path | The primary grounding point and every panel, door, cover, or section that must connect to it | Prevents part of the assembly from being unintentionally isolated |
| Call out the exact hardware | Manufacturer and part number; hardware type, material, thread, and shank code; quantity and location; mounting-hole diameter and tolerance; installation side and direction | Prevents substitutions, incorrect holes, and improperly seated hardware |
| Protect conductive contact areas | Dimensioned masked areas, no-finish zones, contact pads, coating-free threads, and conductive mating surfaces | Keeps the finish from insulating the intended connection |
| Bond doors and removable panels | Specified straps, jumpers, or qualified conductive hinges, along with attachment points and routing | Maintains continuity across components that move or are removed for service |
| Coordinate hardware and finishing | Whether hardware is installed before or after finishing and which surfaces must be coated, masked, or protected | Avoids coated threads, blocked contact surfaces, and finish damage during insertion |
| Share the assembly context | 3D models, part and assembly drawings, wiring diagrams, cable routing, component locations, and door movement | Allows the fabricator to evaluate access and interfaces across the complete assembly |
| Define acceptance criteria | Applicable standards, test points, test method, continuity criteria, resistance limits, and inspection records | Gives inspection an objective basis for accepting the connection |
| Request a DFM review | Hardware compatibility, hole sizes, sheet thickness and hardness, edge distance, tool access, masking, and process sequence | Identifies potential problems while they can still be corrected on the drawing |
How Grounding Features and Electrical Continuity Are Verified
After fabrication and assembly, inspect each grounding feature to confirm it matches the drawing. When the customer’s requirements call for electrical verification, the connection may also need testing before the assembly goes into service.
The process begins with a dimensional and visual inspection. This confirms that each stud, lug, hole, strap, or other grounding feature is present and correctly located. It also verifies the hardware type, orientation, and installation, and confirms that the required contact surfaces remain free of insulating finish.
When specified, ASM may also perform continuity testing or resistance measurements between designated points. The drawing or purchase documentation should identify the test points, method, acceptance criteria, and any inspection records that must be provided.
Keep in mind that a continuity indication only confirms that a conductive path exists. By itself, it doesn’t establish that the path meets a specified resistance limit, can carry the required fault current, or complies with a particular standard. The testing method and acceptance criteria must match the customer-defined requirement.
The clearer those requirements are before fabrication, the easier it is to inspect and verify the finished assembly against them.
Catch Grounding Problems Early With a DFM Review
Whether it’s a forgotten removable panel, an ordinary hinge assumed to be conductive, or a missing masking callout around a contact surface, most grounding problems begin with a small assumption or missed detail rather than a major design flaw.
And while the cost of a self-clinching insert, weld stud, or bonding strap is usually minimal when it’s included in the original design, discovering a grounding problem after fabrication is a different story. At that point, correcting it may require secondary machining, coating removal, replacement hardware, an added jumper, refinishing, or even a remade part. Any of those steps can add cost and delay the project.
An early Design for Manufacturing (DFM) review(opens in new tab) allows ASM to catch these issues when the fix is still a drawing change rather than rework on a finished part. Our team can review hardware compatibility, hole sizes, sheet thickness and hardness, edge distance, tool access, masking requirements, finishing sequence, and strap routing. Because ASM supports fabrication, hardware insertion, finishing, and sheet metal assembly(opens in new tab), our team can see how one decision will affect the rest of the process.
Although the customer still defines the electrical requirements, we can help ensure the physical features can be manufactured and assembled as intended. If your next project includes grounding features, send us the 3D model, drawings, and electrical requirements. We’ll review the design and help resolve hardware, masking, access, and assembly questions before production begins. Request a quote(opens in new tab) to get started.