CSA C22.2 No. 248.2-00 (2005): Technical Overview of Class C Low-Voltage Fuses

CSA C22.2 No. 248.2-00 (2005) is a foundational standard within the Canadian Electrical Code, Part II series, specifically addressing low-voltage fuses of Class C. Established by the Canadian Standards Association and reaffirmed in 2005, this standard provides comprehensive requirements for Class C fuse links, fuse holders, and associated accessories intended for use in electrical distribution systems up to 600 V ac. As a member of the harmonized UL/CSA 248 series, it ensures interoperability between Canadian and U.S. markets while maintaining stringent safety and performance benchmarks.

1. Scope and Application

CSA C22.2 No. 248.2-00 applies to Class C low-voltage fuses rated up to 600 V ac and 600 A, with an interrupting capacity of up to 200 kA RMS symmetrical. These fuses are intended for use in accordance with the Canadian Electrical Code, Part I (CSA C22.1) for overcurrent protection of branch circuits, feeders, and motor circuits. Class C fuses are current-limiting devices, meaning they act quickly to clear faults before current reaches its peak, thereby reducing thermal and mechanical stress on downstream equipment.

The standard covers both fuse links and matching fuse holders, including non-renewable and renewable types, as well as those designed for dimple or rejection features that prevent insertion of lower‑interrupting-class fuses. Specifically excluded are fuse types covered by other parts of the CSA C22.2 No. 248 series (e.g., Class G, H, J, L, R, T) and fuses for direct-current applications.

2. Technical Requirements and Performance Criteria

Class C fuses must satisfy a rigorous set of technical requirements to ensure safe and reliable operation under normal and fault conditions. The table below summarizes key parameters defined in CSA C22.2 No. 248.2-00.

Parameter	Requirement	Test/Compliance Notes
Voltage rating	Up to 600 V ac (50/60 Hz)	Dielectric withstand test at 1500 V between live parts and enclosure.
Current rating (A)	1 to 600 A (standard ampere ratings)	Includes 1, 3, 6, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 300, 400, 500, 600 A.
Interrupting rating	200 kA RMS symmetrical (maximum)	Verified by short-circuit tests at rated voltage and power factor 0.45–0.50.
Overload performance	110% of rated current for ≥4 h (non‑calibrated) or 135% for specific durations	No opening or damage during the overload endurance test.
Temperature rise	Max 95 K rise above ambient at rated current (continuous)	Measured on fuse terminals; ambient still air at 25 °C.
Clearing time (time‑current)	Within defined curves at 200%–500% rated current	Fuse must open within the maximum clearing time envelope; see standard annex for exact limits.

2.1 Time‑Current Characteristics

The standard defines specific time‑current zones for Class C fuses to ensure coordination with downstream devices. At 200% of rated current, the fuse must clear within 5 minutes for rated currents ≤ 100 A, and within 10 minutes for larger ratings. At 500% of rated current, clearing times are typically less than 10 seconds. These characteristics enable Class C fuses to withstand motor starting inrush while providing fast short‑circuit protection.

2.2 Construction and Dimensions

Class C fuse links are defined by precise physical dimensions that include a rejection (dimple) feature on the ferrule end caps. This prevents their insertion into holders designed for lower‑interrupting classes. CSA C22.2 No. 248.2-00 specifies overall length, diameter, width of rejection ears (if present), and contact surface dimensions. Fuse holders must meet temperature rise, voltage drop, and retention force criteria to maintain reliable electrical connections.

3. Construction and Marking Requirements

Every Class C fuse intended for certification under this standard must be clearly and durably marked with the following information:

Manufacturer’s name, trademark, or identifying symbol
Catalog or model number
Rated voltage (V ac) and rated current (A)
Interrupting rating (kA)
Class designation: “CLASS C”
CSA file number or certification mark
Current‑limiting symbol (if applicable)

Materials used in fuse construction must be capable of withstanding the thermal and mechanical stresses imposed by rated and fault conditions. Common materials include high‑temperature ceramic tubes, copper or copper‑alloy elements with silver alloy joints, and silica sand filler for arc extinction. Fuse holders must incorporate rejection features that accept only Class C fuses, and must provide sufficient grip force to prevent accidental dislodging.

Harmonization Benefit: CSA C22.2 No. 248.2-00 is harmonized with UL 248-2 (Standard for Low-Voltage Fuses – Part 2: Class C). Manufacturers who meet one standard are considered to meet the other for the most part, simplifying bi‑national certification and reducing testing costs.

4. Compliance and Certification Notes

Compliance with CSA C22.2 No. 248.2-00 is mandatory in Canada for fuses installed under the Canadian Electrical Code, Part I. Certification is typically performed by an accredited organization such as CSA Group or Intertek. The certification process includes full type‑testing of representative samples covering all ratings in a family, followed by periodic factory inspections and surveillance tests.

Installation Tip: Always verify that the full-load current, available fault current, and system voltage are within the fuse’s marking. Class C fuses are designed for distribution equipment rated up to 600 V ac only; do not use in DC circuits unless specifically listed.

Compatibility Alert: Class C fuses have distinct dimensions and rejection features that differ from Class H, K, or R fuses. They must only be installed in fuse holders marked “CLASS C” or specifically designed for their acceptance features. Forcing a Class C fuse into an incompatible holder can result in arcing, overheating, or loss of overcurrent protection.

Interruption Hazard: Never use a Class C fuse in a circuit where the available fault current exceeds its marked interrupting rating (typically 200 kA RMS). Such application can lead to violent fuse rupture, fire, or injury. If the available fault current is higher, select a fuse with a higher interrupting capacity (e.g., Class L or Class R).

For compliance audits, the standard requires documentation of overload and short‑circuit test results, temperature rise data, and dimension accuracy. Fuses that have passed CSA certification carry the CSA monogram or mark; the lack of such mark means the product has not been verified to this standard.

5. Frequently Asked Questions

Q: Can I replace an existing Class H fuseholder with a Class C fuse and holder without changing the equipment?
A: No. Class C fuses have different dimensions and rejection features. The entire fuseholder must be replaced with a Class C-rated holder. The panelboard or disconnect must also be rated for the higher interrupting capacity if Class C is used.

Q: Are Class C fuses suitable for motor starting applications?
A: Yes, provided the motor starting current and duration are within the time‑current withstand limits. Class C fuses have a moderate time delay (typically 4–10 seconds at 500% rating) which is adequate for general motor starts. For heavy starting duty, a Class CC or Class J fuse with higher time delay may be preferred.

Q: What is the main difference between Class C and Class G fuses?
A: Class G fuses are rated at 480 V ac and have a smaller physical size and lower interrupting rating (100

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