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Quick Answer: Replacing Your Fuse
To replace a fuse in a rail-mounted holder like the CNC RT18, first ensure the circuit is under no-load conditions, ideally with the power completely cut off. Open the hinged fuse carrier and, using insulated needle-nose pliers, remove the blown cylindrical link. Replace it with a new link of the exact same model, size, and rated current. Never substitute a fuse with copper wire. Ensure the new link has firm contact with the support before closing the carrier.
Understanding the RT18 Series Structure
The RT18 series is a cylindrical contact cap fuse protector designed for distribution circuits with AC 50Hz and rated voltages up to 500V (or 690V for RT18L models). The system consists of two primary components: the fuse holder (base and carrier) and the fuse link.
- The Fuse Link: Contains the melt tube, quartz sand for arc quenching, and cylindrical caps.
- Arc Quenching: When overcurrent occurs, the melt fuses, and the internal quartz sand extinguishes the resulting arc to protect the circuit.
- Visual Indicators: Models designated with an “X” (e.g., RT18-32X) feature a neon light or LED that illuminates when the fuse is blown.
Selecting the Right Fuse Link: gG vs. aM
According to IEC 60269 standards, RT18 fuse links are divided by application:
- “gG” Type: Ordinary fuse protectors providing a full range of breaking capacity for general distribution.
- “aM” Type: Specialized for motor protection, offering partial breaking capacity to handle high-startup currents.
Technical Specifications & Selection Table
Proper selection is critical for safety. The following table highlights the dimensions and ratings for the RT18 series:
| Holder Model | Assorted Fuse Link Size (mm) | Rated Current (A) | Rated Voltage (V) |
|---|---|---|---|
| RT18-32 | 10 x 38 | Up to 32A | 380V / 500V |
| RT18-63 | 14 x 51 | Up to 63A | 380V / 500V |
| RT18L-125 | 22 x 58 | Up to 125A | 690V |
Professional Installation & Maintenance Protocols
To maintain safety and performance in your facility, follow these industrial requirements:
- Mounting: Install on standard 35mm DIN rails (EN 60715). The mounting plane should not exceed an inclination of ±5°.
- Electrical Clearance: Ensure an electrical clearance of >8mm and a creepage distance of >10mm.
- Wiring: Recommended cross-sectional areas include 6mm² for 32A, 16mm² for 63A, and 35mm² for 125A.
- Load Warning: The fuse holder must never be used as a switch to connect or disconnect a load.
Important Note: RT18 series products are not suitable for capacitor cabinets; CNC Electric recommends the RT16-00 knife-type fuse for those specific applications.
Frequently Asked Questions
What are the required environmental conditions for RT18 fuses?
They should operate in ambient temperatures between -5°C and +40°C (average ≤35°C). The installation altitude should not exceed 2000m, and they should be stored in a dry environment with no more than six layers of stacking.
How do I know if the fuse link is blown?
If your model has the “X” signal device, the light-emitting diode (LED) will light up upon fusing. You should check the indicator frequently to detect single-phase or lack-of-phase operation.
Can I replace a fuse with a different current rating if the original isn’t available?
No. You must replace the blown link with a new one of the same model, size, and rated current. Using an incorrect rating can compromise circuit protection and lead to equipment failure or fire hazards.
What should I inspect after unpacking a CNC RT18 fuse?
Verify the nameplate matches the box, check for loose or fallen rivets on the support, and inspect the ceramic tube for cracks or leaking quartz sand. If any of these issues are found, do not put the product into use.
