Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Understanding CSA C22.2 No. 248.16-00 (2004): Technical Requirements for Class T Fuses in Low-Voltage Applications
A Comprehensive Guide to the Canadian Standard for Type T Fuses
Scope and Purpose
CSA C22.2 No. 248.16-00 (2004) is the Canadian national standard that covers supplemental requirements for Class T low-voltage fuses, harmonized with UL 248-16. Class T fuses are compact, high-performance current-limiting devices designed for applications requiring high fault current interruption and space savings. This standard applies to fuses rated 600 V AC or less, 600 V DC or less, with current ratings from 1 A to 600 A. It defines the dimensions, electrical characteristics, and testing protocols to ensure safe and reliable operation in branch circuits, service entrance equipment, and panelboards. The standard is part of the CSA C22.2 No. 248 series, which aligns with IEC 60269 and UL 248 standards for global harmonization.
Technical Requirements
Construction and Dimensions
Class T fuses feature a compact cylindrical body with blade-type terminals, designed to fit proprietary fuse holders with rejection features that prevent substitution with other fuse classes. The standard specifies two major dimensional groups based on current rating:
| Rating Range (A) | Overall Length (in) | Diameter (in) | Terminal Width (in) |
|---|---|---|---|
| 1–30 | 2.125 ± 0.031 | 0.406 ± 0.016 | 0.375 ± 0.016 |
| 35–60 | 2.375 ± 0.031 | 0.531 ± 0.016 | 0.500 ± 0.016 |
| 65–100 | 2.750 ± 0.031 | 0.719 ± 0.016 | 0.688 ± 0.016 |
| 110–200 | 3.125 ± 0.031 | 1.000 ± 0.016 | 0.938 ± 0.016 |
| 225–400 | 3.625 ± 0.031 | 1.250 ± 0.016 | 1.188 ± 0.016 |
| 450–600 | 4.375 ± 0.031 | 1.625 ± 0.016 | 1.500 ± 0.016 |
Additionally, fuse terminals must have a minimum thickness of 0.032 in for ratings ≤ 100 A and 0.047 in for higher ratings. Ferrous materials are permitted only if they do not affect fuse performance.
Electrical Performance
Key electrical requirements include:
- Interrupting Rating: 200 kA RMS symmetrical for AC circuits, 100 kA for DC circuits.
- Current Limitation: Under short-circuit conditions, the fuse must limit the peak let-through current and I²t energy to values defined in the standard.
- Time-Current Characteristics: Fuses must open within specified time for overloads (e.g., 135% of rating within 1 h, 200% of rating within 2 min for ratings ≤ 60 A).
- Voltage Drop: At rated current, the voltage drop across the fuse shall not exceed the values given in the standard (typically ≤ 0.3 V for ratings ≤ 200 A).
- Overload and Endurance: The fuse must carry 110% of rated current for 4 h without opening, and must withstand 50 cycles of opening at 200% of rated current.
Tip: When selecting Class T fuses for motor circuits, ensure the time‑current curve is coordinated with the motor starting inrush to avoid nuisance blowing. The fast-acting nature of Class T fuses may require oversized ampacity in certain applications.
Implementation Highlights
Class T fuses are widely used in: commercial and industrial service entrance equipment, panelboards, feeder circuits, and branch circuit protection where high short‑circuit current ratings are needed. Their compact size allows for mounting in smaller enclosures compared to Class R or Class J fuses.
Designers must pay attention to the rejection feature incorporated in both the fuse and the holder. The holder has a specific slot that allows only the matching Class T fuse to be inserted, preventing interchangeability with other classes. This is critical for maintaining the interrupting rating and current‑limiting performance.
Class T fuses are typically used in combination with fusible disconnects or dedicated fuse blocks. The standard requires that the fuse holder or mount be made of non‑combustible, arc‑resistant material and be marked with “FOR USE WITH CLASS T FUSES ONLY”.
Warning: Class T fuses have limited DC interrupting ratings (100 kA) and are not suitable for all DC applications. Always verify the DC voltage rating and consider that DC arcs are harder to extinguish than AC arcs.
For selective coordination (series ratings) between a Class T fuse and downstream overcurrent devices, engineers must consult manufacturer coordination tables. The fuse’s high interrupting capacity often allows it to serve as the main device in a series‑rated combination, provided the combined interrupting rating does not exceed 200 kA.
Compliance Notes
To obtain recognition under CSA C22.2 No. 248.16-00 (2004), fuses must be tested by an accredited laboratory (e.g., CSA or UL) and marked with the appropriate certification symbols. The standard is a mandatory part of the Canadian Electrical Code (CEC), and fuses must bear the CSA monogram or an equivalent certification mark.
Key compliance requirements:
- Manufacturing Follow‑Up: Certified factories undergo periodic unannounced inspections to verify ongoing compliance against construction and performance requirements.
- Marking: Each fuse must be permanently marked with the manufacturer’s name or trademark, catalog number, voltage rating, interrupting rating, and the CSA certification mark.
- Documentation: Instructions for proper mounting, replacement, and coordination must be supplied with fuse holders or published in product literature.
Compliance Benefit: Using CSA‑certified Class T fuses ensures acceptance by all Canadian electrical authorities, simplifies installation inspection, and confirms the product meets the rigorous performance criteria required for high‑fault‑current applications.
It is important to note that the 2004 edition may have been reaffirmed or amended; users should verify the latest edition in force. The standard is harmonized with UL 248-16, but minor deviations exist—mainly regarding marking and test voltages. Always refer to the Canadian version when applying products in Canada.
Danger: Using an uncertified or improperly coordinated Class T fuse can lead to catastrophic failure during a short circuit, including violent fuse rupture or inability to clear the fault. Always replace fuses with the exact same type and rating as specified by the equipment manufacturer.
Frequently Asked Questions
Q: What is the difference between Class T and Class J fuses?
A: Class T fuses are physically smaller and offer higher interrupting ratings (200 kA AC) than most Class J fuses. However, Class T fuses have lower DC ratings and are not interchangeable due to different rejection features. Class J fuses typically have longer time‑delay characteristics for motor starting.
A: Class T fuses are physically smaller and offer higher interrupting ratings (200 kA AC) than most Class J fuses. However, Class T fuses have lower DC ratings and are not interchangeable due to different rejection features. Class J fuses typically have longer time‑delay characteristics for motor starting.
Q: Can Class T fuses be used in DC circuits?
A: Yes, but only within the DC voltage and interrupting ratings specified by the manufacturer. The standard requires testing at 100 kA DC for ratings up to 600 V DC. Always consult the product datasheet for DC ratings, which may differ from AC ratings.
A: Yes, but only within the DC voltage and interrupting ratings specified by the manufacturer. The standard requires testing at 100 kA DC for ratings up to 600 V DC. Always consult the product datasheet for DC ratings, which may differ from AC ratings.
Q: How do I verify if a Class T fuse is CSA certified?
A: Look for the CSA monogram or the CSA‑C/US mark (for compliance with both Canadian and US standards) on the fuse body. The manufacturer’s name and catalog number should also be present. You can verify certification online through the CSA Product Listing database.
A: Look for the CSA monogram or the CSA‑C/US mark (for compliance with both Canadian and US standards) on the fuse body. The manufacturer’s name and catalog number should also be present. You can verify certification online through the CSA Product Listing database.
First issued 2000, reaffirmed 2004. This article references CSA C22.2 No. 248.16-00 (2004). Technical content accurate as of 2026.