Choose a PCB mounted PTC enclosure around the approved limiter assembly, not around the dimensions of a bare thermistor. A component carrier and an outer electrical enclosure perform different jobs. Repeated arcing means the electrical fault must be resolved before either housing returns to service.
For a replacement, retain the documented component package, establish its operating clearances and temperature limits, then size the outer enclosure. Do not assume a new metal box makes a damaged board or an unidentified limiter safe.
Resolve the arc damage before selecting the box
A PTC inrush-current limiter increases resistance as its temperature rises. Its behavior depends on the circuit, thermal conditions and operating sequence. A matching disk diameter or cold resistance does not establish electrical interchangeability.
If the original insulating carrier is damaged, establish whether it belongs to a complete, manufacturer-specified component assembly. It may provide terminal positioning, insulation, mechanical retention and thermal spacing that an improvised holder cannot reproduce.
Before measuring the installation, isolate all supplies, apply lockout/tagout and verify absence of voltage. Address stored capacitor energy through the equipment manufacturer's documented procedure. Do not energize an exposed damaged assembly to locate the arc.
Investigate these possible causes rather than treating them as confirmed diagnoses:
- Loose or damaged connections that create local heating or arcing.
- Contamination, moisture or conductive debris across insulation surfaces.
- Incorrect component selection, repeated restart duty or a failed bypass circuit, where fitted.
- Inadequate spacing, damaged insulation or carbonized PCB material.
- A downstream fault or protection arrangement that needs review.
Replace damaged parts through the equipment manufacturer's documented repair route. Carbonized laminate can remain conductive; covering it with a new carrier is not a repair.
Define the environment around the limiter
Describe the conditions outside the outer enclosure and around the component separately. A dry control cabinet can still contain conductive dust, process vapors or condensation.
Record whether the installation faces indoor dust, dripping liquid, outdoor rain, hose-directed water or corrosive cleaning chemicals. Include ambient temperature, humidity, vibration and the frequency of enclosure access. These conditions determine the enclosure design, seals and cable-entry arrangement.
Also record what happens during operation. A limiter may experience a different thermal cycle during repeated starts than during continuous running. Nearby power resistors, rectifiers and transformers can raise its local ambient temperature above the cabinet average.
For the overall board arrangement, use the PCB enclosure selection guidance. This replacement decision adds a narrower requirement: the enclosure must accommodate the approved limiter package without changing its intended thermal or insulating arrangement.
Do not place a small protective cover tightly around the limiter unless its documentation permits that installation. Restricting airflow can change its operating behavior and overheat adjacent insulation.
Select an environmental rating, not an arc-containment claim
Choose the enclosure type from the actual exposure. A dry indoor installation may need a different design from a dusty process area or a washdown location.
For example, NEMA Type 12 addresses indoor dust, dirt and dripping liquids. Type 4 addresses hose-directed water, while Type 4X adds corrosion resistance. Our custom enclosure ratings are manufacturer ratings for the specified design; the enclosures are not UL listed.
These environmental ratings do not establish that a box can contain an internal electrical arc. They also do not approve the thermistor, its carrier, PCB insulation or protective-device coordination.
Do not specify a heavier metal box as the remedy for repeated arc damage. The arc flash rated enclosure explanation addresses why environmental protection and internal electrical-fault performance are separate questions.
If the equipment specification requires third-party evaluation, identify that requirement before ordering. A suitable empty enclosure does not establish the compliance of the completed electrical assembly.
Choose the outer material separately from the carrier
The outer enclosure material answers environmental and mechanical questions. The component carrier answers electrical insulation, temperature and retention questions. Do not substitute one decision for the other.
For the outer enclosure, powder-coated carbon steel can suit indoor and sheltered industrial panels. Our custom material options also include 304 stainless steel and 316L stainless steel. Consider 316L where salt air, brine or chloride exposure makes corrosion resistance a stronger concern.
Chemical exposure still needs a compatibility review. Specify the chemical, concentration, temperature and cleaning method rather than relying on a stainless grade alone. Gaskets and cable-entry seals need the same review.
For an insulating carrier, identify the documented material, temperature capability and electrical properties of the approved assembly. A generic plastic cup is not equivalent merely because the component fits inside it.
A metal outer enclosure requires an appropriate protective bonding arrangement. Keep live terminals clear of the enclosure, fasteners and backplate. The enclosure grounding and bonding guide covers the protective bonding fundamentals without treating the enclosure as circuit insulation.
Size for the complete assembly and its heat
Start with the installed assembly envelope, including the PCB, standoffs, limiter carrier, terminals and connector bodies. Add space for wiring bends, connector removal and access to mounting screws.
Measure in all three axes. A board that fits across the backplate can still foul the door through a tall component or a connected cable. Include the full reach of mounting studs and door-mounted hardware.
Electrical separation is not a universal clearance around the thermistor. Establish air clearance and creepage requirements from the applicable equipment standard and documented component installation conditions. Working voltage, transients, pollution degree, insulation material and altitude can affect those requirements.
Thermal spacing is a separate constraint. The component documentation may require separation from the PCB or nearby materials even when electrical spacing is adequate.
Calculate enclosure heat from the actual operating losses of every installed device. Do not use the limiter's cold resistance as its steady-state resistance. Include startup duty, normal operation and permitted restart conditions in the assessment.
For illustration, a 5 W continuous loss with an established enclosure thermal resistance of 2 °C/W produces a 10 °C average rise. That calculation does not predict the limiter's surface temperature or the air temperature beside it.
Use the PCB heat in a sealed enclosure guidance for the broader heat balance. Verify component temperatures in the completed assembly under the defined operating conditions before release.
Mount the board without loading the limiter
Support the PCB through its intended mounting locations. Use suitable standoffs and controlled fastener engagement. Check the underside for solder joints, exposed conductors and mounting hardware that could reduce electrical separation.
Do not use the thermistor leads as structural supports for the board or an improvised carrier. Preserve the component manufacturer's specified mounting method and lead geometry. Board bending can load solder joints and move live parts toward nearby metalwork.
Set assembly torque from the actual fastener, standoff and PCB arrangement. The PCB mounting torque guidance explains why a generic screw torque can damage a board before the joint is secure.
Secure incoming cables independently of their PCB terminations. Cable movement must not pull on limiter connections or drag wiring against a hot surface. Follow the cable strain relief guidance when locating entries and internal restraints.
Place cable entries where their fittings, locknuts and internal cable bends remain accessible. Avoid directing cables over the limiter or obstructing its required cooling space. Seal unused openings with suitable components, and review the completed entry arrangement against the intended environmental rating.
For factory openings, the custom stainless enclosure and cutout options support drawing-based review. New openings do not automatically preserve a rating; include the fitted components and sealing details in that review.
Put the complete installation on the order
We build custom enclosures with specified material, width, height, depth and cutouts, from a quantity of one. Define the enclosure around the approved electrical arrangement rather than asking the enclosure drawing to resolve an unidentified component.
Use the following information for the enclosure specification and approval drawing.
| Item | What to specify |
|---|---|
| Electrical assembly | Approved limiter assembly identification, PCB drawing and documented mounting conditions |
| Fault repair status | Confirmation that arc damage and its cause have been addressed before reuse |
| Environment | Indoor or outdoor location, dust, water, chemicals, humidity and ambient temperature |
| Enclosure rating | Required environmental type and any separate project evaluation requirements |
| Outer material | Selected material and the exposure supporting that choice |
| Dimensions | Width, height and depth, with the required usable internal envelope clearly identified |
| PCB mounting | Hole coordinates, datum, standoff height, fastener engagement and underside clearance |
| Insulation space | Required clearance, creepage and exclusion zones around live parts and hardware |
| Thermal conditions | Operating losses, restart duty, maximum local temperatures and required thermal spacing |
| Cable entries | Cutout dimensions, fitting details, sealing method, cable bends and strain relief |
| Bonding and access | Bonding locations, service access and removal space for the approved component assembly |
Mark critical spaces on the drawing rather than leaving them implied. Distinguish electrical separation, thermal exclusion zones and service access. An opening that clears a connector may still leave insufficient room to remove it.
Approve the enclosure only after those requirements agree with the electrical assembly documentation. The final check is not simply whether the board fits. It is whether mounting, insulation, heat control and environmental protection remain suitable together.
Enclosures for this job
Catalog sizes that suit the job this article answers, picked from its subject; open one for its full specifications.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 16 × 12 × 8 in | 304 stainless | 16 x 12 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 24 × 20 × 8 in | 304 stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 30 × 24 × 10 in | 304 stainless | 30 x 24 x 10 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Can I replace only the plastic housing around a PTC limiter?
Use a separate carrier only when the component manufacturer documents it as a suitable replacement. The carrier may establish insulation, terminal spacing and thermal conditions. If it belongs to a complete limiter assembly, replace that assembly through the documented repair route rather than copying its shape.
Are disk size and cold resistance enough to select a replacement PTC?
No. Disk dimensions and cold resistance do not establish voltage capability, energy handling, thermal behavior or permitted restart duty. Establish the approved assembly from equipment documentation or manufacturer support. Enclosure selection should follow that identification, not substitute for it.
Will a metal enclosure make a repeatedly arcing limiter safe?
A metal enclosure can provide environmental protection and a protective bonding arrangement, but it does not correct an electrical fault. An environmental rating does not establish internal arc containment. Resolve the damage mechanism, replace affected parts and assess the completed assembly before returning it to service.
How much space should I leave around a PCB mounted PTC?
There is no universal spacing that covers every PTC assembly. Use documented component mounting requirements and the applicable equipment standard. Check electrical clearance and creepage separately from thermal spacing, cable routing and service access. Nearby metal hardware must remain outside the required electrical separation.
Can a PTC inrush limiter operate inside a sealed enclosure?
It can, provided the approved component installation permits it and the completed assembly meets its temperature limits. Assess all internal losses, local heating and restart duty. A sealed enclosure's average air temperature does not establish the limiter surface temperature or the temperature of nearby insulation.
