-
-
-
Mitsubishi Electric Corporation
Mitsubishi Electric Corporation E12474642 FUSIBLE PLUG CAN USE T7W973507
FUSIBLE LINKS
# Fusible Links - HVAC Thermal Safety Fuses
Shop replacement fusible links (thermal fuses) for furnaces, air handlers, and HVAC equipment. We stock temperature-rated thermal cutoff devices in all ratings at our Westland, Michigan warehouse. One-time safety fuses that prevent fires and equipment damage.
## Why Buy Fusible Links From Technical Hot & Cold?
**Complete Temperature Range**
Fusible links rated from 150°F to 300°F+ for various HVAC applications and safety requirements.
**Quality Safety Components**
Reliable thermal fuses from Bussmann, Littelfuse, and OEM manufacturers. UL-listed for safety compliance.
**Same-Day Shipping**
Safety fuses in stock ship today when ordered before 3PM EST from our Westland warehouse.
**Multi-Pack Pricing**
Fusible links are inexpensive. Stock multiple spares - they're single-use safety devices.
## What is a Fusible Link?
A fusible link (thermal fuse) is a one-time safety device that:
- Opens permanently when temperature exceeds rating
- Prevents overheating and fires
- Non-resettable - must be replaced after trip
- Simple, reliable temperature cutoff
- Required safety device in many applications
**Located:** Various locations in HVAC equipment near heat sources
**Function:** Over-temperature protection
## How Fusible Links Work
**Thermal Operation:**
### Normal Operation:
- Current flows through link
- Temperature below rating
- Link remains closed
- Circuit complete
- Equipment operates normally
### Over-Temperature Condition:
1. **Temperature Rises**
- Equipment malfunction
- Airflow blockage
- Fire condition
- Other overheating
2. **Link Reaches Rating**
- Internal element melts
- Opens circuit instantly
- One-time use
- Cannot reset
3. **Circuit Opens**
- Power interrupted
- Equipment shuts down
- Prevents further heating
- Fire prevented
4. **Replacement Required**
- Must install new link
- Find and fix cause
- Never bypass!
- Test system
**vs. Resettable Switches:**
- Fusible links are permanent
- Can't accidentally reset
- Forces investigation
- Ultimate safety
## Types of Fusible Links
### Axial Lead Thermal Fuses
Most common type in HVAC.
**Features:**
- Wire leads on each end
- Small cylindrical body
- Various temperature ratings
- Easy to install
**Construction:**
- Ceramic or epoxy body
- Internal thermal element
- Wire leads for connection
- Insulated housing
**Applications:**
- Furnace controls
- Blower motors
- Transformers
- Any over-temp protection
**Temperature Ratings:**
- 150°F, 160°F, 170°F
- 180°F, 190°F, 200°F
- 212°F, 225°F, 240°F
- 250°F, 300°F, and more
### Disc-Type Thermal Fuses
Flat disc configuration.
**Features:**
- Flat round body
- Terminal connections
- Similar function
- Different mounting
**Applications:**
- Motor windings
- Transformers
- Control panels
- Surface mounting
### High-Temperature Links
For extreme applications.
**Ratings:**
- 300°F+
- 400°F+
- Industrial applications
- Special equipment
**Construction:**
- Heavy-duty materials
- Higher current ratings
- Robust design
## Common HVAC Applications
### Furnace Blower Motors
**Protection:**
- Motor winding over-temperature
- Prevents motor fire
- Usually 150-170°F rating
- Inside motor or control
**Location:**
- Embedded in motor windings
- Or external on motor housing
- Or in control circuit
**Function:**
- Opens if motor overheats
- Prevents motor fire
- Forces investigation
- Replace motor or link
### Transformers
**Protection:**
- Transformer over-temperature
- Overload protection
- Fire prevention
- Usually 170-200°F
**Location:**
- Inside transformer housing
- Inline with primary winding
- Built into some transformers
**Function:**
- Opens on transformer overload
- Prevents fire
- Transformer likely needs replacement too
### Limit Switch Backup
**Redundant Protection:**
- Backup to limit switch
- If limit fails
- Last line of defense
- Usually 200-250°F
**Location:**
- Near heat exchanger
- In plenum
- High-temperature area
**Function:**
- Limit switch is primary
- Fusible link is backup
- Opens if limit fails
- Prevents catastrophic overheating
### Control Boards
**Circuit Protection:**
- Prevent board fires
- Over-current protection
- Transformer overload
- Usually 200-240°F
**Location:**
- On control board
- Inline with transformer
- Power supply circuit
## Fusible Link Specifications
### Temperature Ratings:
**Common HVAC Ratings:**
- **150°F** - Motor protection (low)
- **165°F** - Motor protection (standard)
- **184°F** - Motor protection (higher)
- **192°F** - Transformer protection
- **216°F** - Backup high limit
- **240°F** - Extreme over-temp
- **300°F** - Very high applications
**Tolerance:**
- Usually ±9°F
- Tight tolerance critical
- Must be accurate
### Electrical Ratings:
**Current:**
- 10A, 15A, 20A typical
- Must handle normal circuit load
- Not the same as breaker rating
- Thermal, not electrical protection
**Voltage:**
- 120V, 240V typical
- Some rated 24V
- Must match circuit
- Check specifications
### Physical Dimensions:
**Axial Lead:**
- Body: 1/4" to 1/2" diameter
- Length: 3/8" to 1" typical
- Lead length: 2-4" typical
- Lead wire gauge: 18-22 AWG
**Color Coding:**
- Body color indicates rating (sometimes)
- Read markings carefully
- Verify temperature rating
## Selecting the Right Fusible Link
### Critical Specifications:
1. **Temperature Rating**
- Must match application
- Too low = nuisance trips
- Too high = won't protect
- Use exact rating
2. **Current Rating**
- Must handle normal current
- Typically 10-20A
- Not overload protection
- Thermal protection only
3. **Voltage Rating**
- Match circuit voltage
- 24V, 120V, or 240V
- Adequate for application
4. **Physical Size**
- Must fit in space
- Lead length adequate
- Body size appropriate
5. **Response Time**
- Some fast-acting
- Some slow-blow
- Match to application
### Replacement Selection:
**Exact Replacement Best:**
- Same temperature rating
- Same current rating
- Same physical size
- Match original exactly
**Universal Options:**
- Some fusible links universal
- Verify all specifications
- When exact unavailable
- Check compatibility
## When Fusible Links Trip
### ⚠️ INVESTIGATION REQUIRED
**Fusible link opened = serious problem!**
**DO NOT simply replace and restart:**
- Link tripped for a reason
- Dangerous condition exists
- Must find and fix cause
- Could be fire hazard
### Diagnostic Steps:
1. **Identify Cause**
- Why did temperature exceed rating?
- Equipment malfunction?
- Airflow blockage?
- Other issue?
2. **Common Causes:**
- **Motor Protection:**
* Seized motor
* Bad capacitor
* Overloaded motor
* Poor ventilation
- **Transformer:**
* Shorted circuit
* Overload
* Defective transformer
- **Limit Switch Backup:**
* Failed limit switch
* Restricted airflow
* Over-firing
* Blower failure
3. **Inspect Equipment**
- Visual inspection for damage
- Check for burning/melting
- Test related components
- Measure voltages/currents
4. **Fix Root Cause**
- Replace failed motor
- Fix airflow restriction
- Replace bad transformer
- Repair whatever caused overheating
5. **Replace Fusible Link**
- Use correct rating
- Proper installation
- Secure connections
6. **Test and Monitor**
- Operate equipment
- Monitor temperatures
- Watch for proper operation
- No trip = cause fixed
## Fusible Link Installation
**Simple but Critical:**
### Installation Steps:
1. **Turn Off All Power**
- Breaker and switch
- Verify no voltage
- Discharge capacitors
2. **Locate Old Link**
- May be hidden
- Inside motor
- In control panel
- Follow wires
3. **Remove Old Link**
- Cut wires or unplug
- Note wire positions
- May need to unwrap tape
- Extract carefully
4. **Install New Link**
- Same position as old
- Correct orientation (if applicable)
- Don't bend leads excessively
- No strain on connections
5. **Connect Wires**
- Method depends on type:
* Crimp connectors
* Solder connections
* Wire nuts (some)
* Screw terminals
- Secure all connections
- Insulate properly
6. **Secure Link**
- Tape in place (if needed)
- Keep away from sharp edges
- Ensure good heat sensing
- No mechanical stress
7. **Test System**
- Restore power
- Operate equipment
- Monitor operation
- Check temperatures
### Installation Tips:
**Best Practices:**
- Use heat-shrink tubing over connections
- Secure link so it can't vibrate
- Position for accurate temperature sensing
- Don't overtighten if screw terminals
- Keep leads short (reduce resistance)
**Avoid:**
- Excessive bending of leads
- Mechanical stress on body
- Installing wrong temperature rating
- Bypassing the link
- Using electrical tape only (heat shrink better)
## Common Installation Mistakes
❌ **Wrong Temperature Rating**
- Must be exact
- Too low = trips unnecessarily
- Too high = won't protect
- Verify rating
❌ **Poor Connections**
- Loose connections = resistance = heat
- May trip link prematurely
- Secure all connections
- Use proper method
❌ **Wrong Position**
- Link must sense actual temperature
- Too far away = won't protect
- Wrong location = false trips
- Match original position
❌ **Bypassing Link**
- NEVER jumper/bypass
- Defeats safety device
- Fire hazard
- Code violation
## Fusible Link Maintenance
**Inspection:**
- Visual inspection during service
- Check connections tight
- Look for heat damage nearby
- Verify proper type installed
**Replacement Schedule:**
- Replace only when tripped
- Or preventively if:
* Equipment overhauled
* Major repair done
* Age 15+ years
* Showing signs of heat damage
**Testing:**
- Can't really test without destroying
- Continuity test when cool (should be closed)
- If open and hasn't tripped = defective
- But hard to verify until it's needed
**Prevention:**
- Maintain equipment properly
- Change filters regularly
- Address issues promptly
- Prevent conditions that trip links
## Fusible Link FAQs
**Q: Can I reset a fusible link?**
A: NO. Fusible links are one-time use. Once tripped, they must be replaced. This is by design - forces investigation of problem.
**Q: What causes fusible links to trip?**
A: Over-temperature conditions:
- Motor overheating/seizure
- Transformer overload
- Restricted airflow
- Equipment malfunction
- Fire conditions
**Q: Can I bypass a fusible link?**
A: NEVER! Fusible links are critical safety devices that prevent fires. Bypassing creates extreme danger.
**Q: What temperature rating should I use?**
A: Use exact rating of original link. Wrong rating = inadequate protection or nuisance trips.
**Q: Where can I find the temperature rating?**
A: Printed on fusible link body. May be tiny print. Use magnifying glass if needed.
**Q: Can I use a circuit breaker instead?**
A: No. Different function. Fusible links respond to temperature, breakers to current. Both needed.
**Q: Why use fusible link instead of limit switch?**
A:
- Simpler (no adjustment)
- More reliable (no moving parts)
- Backup protection
- Different applications
- Both often used
**Q: How long do fusible links last?**
A: Indefinitely if never tripped. Will last life of equipment under normal conditions.
**Q: Are fusible links expensive?**
A: Very inexpensive! Usually $2-10 each. No excuse not to replace after trip.
**Q: Can a fusible link fail without tripping?**
A: Rare, but possible. Can fail open (nuisance trip) or very rarely fail closed (won't protect). Test for continuity.
**Q: What's the difference between a fusible link and a fuse?**
A: Fusible links respond to temperature (thermal), regular fuses respond to current (electrical). Different protection purposes.
**Q: Can I test a fusible link?**
A: Continuity test when cool - should show continuity (closed). If open when cool, it's blown. Can't test temperature rating without destroying it.
## Troubleshooting Guide
| Symptom | Possible Cause | Solution |
|---------|---------------|----------|
| Equipment won't start | Tripped fusible link | Test continuity, replace if open |
| Fusible link trips repeatedly | Underlying problem | Diagnose and fix root cause |
| New link trips immediately | Wrong rating or still broken | Check rating, fix equipment |
| Equipment overheated | Fusible link didn't trip | Wrong rating or bad link |
## Temperature Rating Quick Reference
| Application | Typical Rating | Purpose |
|-------------|---------------|---------|
| Blower motor protection | 150-170°F | Motor winding protection |
| Blower motor (higher) | 184°F | Motor over-temp |
| Transformer protection | 192°F | Transformer overload |
| Backup high limit | 216°F | Redundant protection |
| Extreme over-temp | 240°F | Last-resort protection |
| High-temperature | 300°F+ | Industrial/special |
## Popular Fusible Link Brands
**Quality Manufacturers:**
- **Bussmann** - Industry standard thermal fuses
- **Littelfuse** - Reliable thermal cutoffs
- **Therm-O-Disc** - HVAC thermal fuses
- **Microtemp** - Temperature fuses
**OEM Brands:**
- Carrier/Bryant - OEM fusible links
- Trane - OEM thermal fuses
- Lennox - OEM safety fuses
- Goodman - OEM thermal cutoffs
## For HVAC Contractors
**Stock Common Ratings:**
- 165°F (motor protection)
- 184°F (motor protection)
- 192°F (transformer)
- 216°F (backup protection)
- Various current ratings
**Service Tips:**
- Always stock extras
- Multi-packs save money
- Customer education important
- Document findings when link trips
**Safety Message:**
- Explain to customers
- Never bypass
- Indicates serious problem
- Proper diagnosis required
**Inventory Strategy:**
- Very inexpensive parts
- Stock multiple ratings
- Keep 5-10 of each common rating
- Excellent service add-on item
## Need Help Selecting a Fusible Link?
Our HVAC parts specialists are here to help! Contact us:
- **Phone:** 734-326-3900
- **Email:** parts@technicalhotandcold.com
- **Hours:** Monday - Friday 8 am - 5 pm
- **Location:** Westland, MI - Local pickup available
**Have the temperature rating from your old link. We'll match it exactly. Buy extras - they're inexpensive and single-use!**
**Browse our fusible link selection below - temperature-rated thermal fuses in stock for immediate shipment!**
Can't find what you're looking for?
If you don't see your model or part, call us! Our friendly technicians are standing by. We can help you find the part you need with guaranteed fitment. Speak with us today at (734) 326-3900.
