Mounting Clips, Brackets and Hardware for Resistors

Mounting Clips, Brackets and Hardware for Resistors
Whether an axial resistor snaps into a spring clip or a power resistor bolts to a chassis, the mounting hardware keeps the part fixed under vibration, shock and thermal cycling. Here is how to choose it.

Reading time: 7 min
Topic: Mounting hardware
Audience: Design engineers, assembly technicians
A resistor that moves is a resistor that fails. Repeated vibration fatigues lead wires, thermal expansion loosens joints, and a body that shifts can short against adjacent parts. Mounting clips, brackets and fasteners are the quiet insurance policy that keeps a resistor exactly where the design expects it to be — for years of thermal cycles, shipping vibration and field abuse.

Clips for Axial and Leaded Resistors
Axial wirewound and film resistors are often held by spring steel clips. A typical clip is a U-shaped or slotted piece of spring metal that grips the cylindrical body and snaps into a holder or a cutout in a chassis or PCB. The clip does several jobs at once:

Locates the resistor firmly so the leads are not the only thing carrying mechanical stress.
For some types, doubles as a heat path from the body to the mounting surface.
Allows the resistor to be replaced without desoldering.
Clip bodies are usually made from spring steel with a corrosion-resistant finish, sometimes tin-plated for better solderability or electrical contact. Choose a clip whose inner diameter matches the resistor body diameter; an undersized clip deforms the body and can crack the ceramic core.

Chassis-Mount Brackets and Flanges
Larger power resistors come in two common forms: an aluminum-housed block with a mounting flange, or a wirewound tube held by an external bracket. In both cases the mounting hardware must do three things:

Hold the part securely under vibration and shock.
Press the case firmly against the heat sink or chassis for good heat transfer.
Survive repeated thermal cycling without loosening.
Two mounting styles
Spring-clip (axial)
Resistor
board / chassis
Flange (power resistor)
Aluminum case
screws + heat sink below
Left: spring clips grip the body. Right: flange screws press the case onto the heat sink.
Figure 1 — Clips suit small axial parts; flanged housings suit power resistors that must couple heat into a sink.
The flange is usually bolted to a chassis or heat sink with machine screws. Washer selection is important: a lock washer or a spring washer keeps the joint tight as the parts expand and contract. For electrically isolated mounting, insert mica or an insulating pad and use insulating shoulder washers so the screw does not touch the flange.

Fasteners: Screws, Nuts and Washers
Table 1 — Fastener roles in resistor mounting
Fastener Job Selection notes
Machine screw Bolt the flange or bracket to the surface Match thread, length and head style to the bracket
Lock / spring washer Prevent loosening from vibration and thermal cycling Almost always worth including on power resistors
Flat washer Spread load, protect the flange surface Use under the head and under the nut
Insulating shoulder washer Isolate the screw from the case Nylon or fiber; needed for isolated mounting
Torque Ensure firm contact without damage Follow the resistor datasheet; overtightening cracks the body
For isolated flange mounting, the screw, washer and any strap must all be isolated — a single metal screw touching the case creates a short path to chassis and defeats the whole purpose.

Vibration and Thermal Cycling Considerations
Field vibration and repeated thermal expansion are the two real tests of mounting hardware. On a vibrating machine, a loosely held resistor can fatigue its own leads in hours. On a hot-cold cycling power stage, metal parts expand and contract at different rates, and a joint without a spring element slowly works loose.

Prefer spring-steel clips and lock washers where vibration is present.
Allow the bracket to accommodate thermal expansion without over-constraining the part.
Keep lead wires short but with a small service loop so they do not pull on the body.
Use thread-locking compound or prevailing-torque fasteners for critical joints, or verify torque after thermal cycling.