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Understanding CSA C22.2 No. 4248.11-07 (2017): Safety Standards for Class H, K, and R Fuseholders
A Comprehensive Technical Guide to the Canadian National Standard for Overcurrent Protection Devices
Scope and Purpose
CSA C22.2 No. 4248.11-07 (2017) is a Canadian national standard developed under the Canadian Electrical Code (CEC) umbrella within the CSA C22.2 series. It specifically covers Class H, K, and R fuseholders rated up to 600 V AC and 600 V DC, with current ratings typically up to 600 A. This standard is harmonized with UL 4248-11 and provides safety requirements for the design, construction, performance, and testing of fuseholders used in overcurrent protection systems.
The primary purpose of this standard is to ensure that these fuseholders provide reliable electrical protection and physical containment of fuse cartridges under normal and fault conditions. It addresses key hazards such as electrical shock, arc flash, fire initiation, and mechanical failure. The standard applies to fuseholders intended for use in accordance with the Canadian Electrical Code, Part I (C22.1).
This edition was originally published in 2007 and reaffirmed in 2017, confirming its continued relevance and technical validity. It forms part of a suite of standards covering various fuseholder classes, including Classes CC, G, J, L, and T.
Technical Requirements
General Construction
Fuseholders under CSA C22.2 No. 4248.11-07 (2017) must be constructed with robust materials that can withstand thermal and mechanical stresses. Enclosures are typically made of thermoset or thermoplastic materials with a minimum flammability rating of V-0 per CSA C22.2 No. 0.16. Live parts must be corrosion-resistant and sized to handle rated current without excessive temperature rise.
Dimensions and Interchangeability
A critical aspect of the standard is dimensional compatibility with standard Class H (rejection), Class K (non-rejection), and Class R (rejection) fuse types. The table below summarizes key contact dimensions for Class R fuseholders (30 A frame):
| Parameter | Minimum (mm) | Maximum (mm) |
|---|---|---|
| Fuse clip spacing (center to center) | 31.8 | 32.5 |
| Contact width | 12.7 | 13.5 |
| Clip thickness (spring material) | 0.8 | 1.6 |
| Barrel clearance (internal depth) | 24.0 | 26.0 |
Class H and K fuseholders are dimensionally similar but lack the rejection features that prevent insertion of non-identical fuse classes. Class R fuseholders include a mechanical barrier or groove that only accepts Class R fuses, which have a corresponding slot.
Electrical Performance
Standard tests include temperature rise, dielectric voltage withstand, short-circuit current interruption, and overload cycling. For example, a 30 A Class R fuseholder must carry its rated current with a temperature rise not exceeding 30 K above ambient when tested under steady-state conditions. The dielectric test is performed at 1000 V plus twice the rated voltage (or 1500 V for 600 V rated devices).
Short-circuit testing is conducted at prospective current levels corresponding to the fuseholder’s interrupting rating, typically 10 kA or 200 kA symmetrical RMS. The fuseholder must contain any arc and prevent external flashover. After the test, the fuseholder must not sustain damage to live parts that would affect subsequent operation.
Endurance and Mechanical Life
Mechanical endurance requires 1000 operations at room temperature without load and 50 switching cycles at rated current and voltage. Contact resistance must remain stable, and no visible wear or loosening of parts is permitted.
Tip: When designing or selecting a fuseholder for a specific Class H, K, or R fuse, always verify the rejection features (if any) and ensure the device is listed for the intended voltage and interrupting rating. Class R fuseholders are preferred for new installations because they prevent misapplication of lower-interrupting Class H fuses.
Implementation Highlights
Harmonization with North American Standards
CSA C22.2 No. 4248.11-07 (2017) is aligned with UL 4248-11 (Fuseholders – Part 11: Class H, K, and R Fuseholders). This harmonization allows manufacturers to certify products for both the Canadian and US markets with minimal additional testing, provided the product meets the common requirements. Differences exist in marking and some Canadian-specific tests, such as the dielectric breakdown test under high humidity conditions.
Practical Application in Electrical Panels
Fuseholders complying with this standard are used in industrial control panels, distribution boards, disconnect switches, and motor control centers. Engineers must consider the type of branch circuit and available fault current when selecting between Class H, K, and R variants. Class R fuseholders are often specified for new construction because they accept only Class R fuses, which have higher interrupting ratings (200 kA) compared to Class H (10 kA).
Important: Class K fuseholders are non-rejection and may accept both Class K and Class H fuses. However, Class K fuses have a higher interrupting rating (200 kA) but still fit into Class H fuseholders. This can create a false sense of security. Always verify the fuseholder’s labeled interrupting rating and do not rely solely on the fuse class to determine system capability.
Wiring and Termination
The standard specifies torque values for screw terminals and pressure‑wire connectors. For copper conductors (AWG 14–2/0), typical torque values are as follows:
| Conductor Size (AWG) | Torque Range (lb‑in) |
|---|---|
| 14–10 | 12–15 |
| 8–6 | 20–25 |
| 4–2 | 30–35 |
| 1–2/0 | 40–45 |
Incorrect torque can cause excessive resistance and overheating, compromising both performance and safety.
Compliance and Certification Notes
Listing and Labeling
Fuseholders conforming to CSA C22.2 No. 4248.11-07 (2017) must be marked with the manufacturer’s name or trademark, catalog number, electrical ratings (volts and amperes), and the CSA certification mark. For Class R devices, the marking must include “Class R” or the appropriate rejection symbol. The standard also requires that fuseholders bear an indication of the maximum allowable fuse interrupting rating, e.g., “For use with 200 kA interrupting rated fuses.”
Field Evaluation and Maintenance
Even though the standard is product-safety oriented, users and field inspectors should verify that fuseholders are correctly matched with the fuse type and that the rejection features are not bypassed (e.g., filing down Class H fuses to fit into Class R holders). Such modifications void certification and create safety hazards.
Best Practice: Always replace fuseholders with the same or equivalent certified model. If upgrading a panel from Class H to Class R fusing, change the fuseholder to a Class R type listed under CSA C22.2 No. 4248.11-07 (2017) to ensure proper rejection and fault protection.
Critical: Never substitute a Class R fuseholder with a Class H or Class K unit in a system requiring rejection features. Class H fuseholders are not tested to withstand the high interrupting current of Class R fuses and may fail violently under fault conditions.
Periodic Reaffirmation and Amendments
The 2017 reaffirmation incorporated minor editorial corrections and updated references to the Canadian Electrical Code Part I. No major technical changes were introduced. Manufacturers holding CSA certification for products under this standard are required to undergo periodic surveillance audits to maintain compliance. The standard is expected to be reviewed again within ten years (target ~2027).
© 2026 Canadian Standards Association (CSA) – This article is for informational purposes only and does not replace the official standard document. Always refer to the latest published edition for certification and legal compliance.
Frequently Asked Questions
Q: What is the difference between Class H and Class R fuseholders under CSA C22.2 No. 4248.11-07 (2017)?
A: Class H fuseholders are non-rejection and accept only Class H fuses (10 kA interrupting rating). Class R fuseholders include a rejection feature (a groove or barrier) that prevents insertion of Class H fuses, ensuring only Class R fuses (200 kA interrupting rating) are installed. Class R holders offer higher fault protection and are required for systems with higher available short-circuit current.
A: Class H fuseholders are non-rejection and accept only Class H fuses (10 kA interrupting rating). Class R fuseholders include a rejection feature (a groove or barrier) that prevents insertion of Class H fuses, ensuring only Class R fuses (200 kA interrupting rating) are installed. Class R holders offer higher fault protection and are required for systems with higher available short-circuit current.
Q: Can I use a Class K fuse in a Class H fuseholder?
A: Yes, Class K fuses have the same physical dimensions as Class H fuses and will fit into a Class H holder. However, the interrupting rating of the combination may be limited by the fuseholder’s rating (typically 10 kA). It is safer to use a Class R holder with Class R fuses to avoid misapplication.
A: Yes, Class K fuses have the same physical dimensions as Class H fuses and will fit into a Class H holder. However, the interrupting rating of the combination may be limited by the fuseholder’s rating (typically 10 kA). It is safer to use a Class R holder with Class R fuses to avoid misapplication.
Q: Are fuseholders covered by this standard acceptable for use in both Canada and the United States?
A: Products certified to CSA C22.2 No. 4248.11-07 (2017) can carry the CSA mark but do not automatically meet UL 4248-11 requirements for US installation. Many manufacturers obtain dual‑listing marks (e.g., CSA with NRTL recognition) to demonstrate compliance with both standards. Check the marking for a “US” or “C‑US” indicator.
A: Products certified to CSA C22.2 No. 4248.11-07 (2017) can carry the CSA mark but do not automatically meet UL 4248-11 requirements for US installation. Many manufacturers obtain dual‑listing marks (e.g., CSA with NRTL recognition) to demonstrate compliance with both standards. Check the marking for a “US” or “C‑US” indicator.
Q: What are the main changes in the 2017 reaffirmation compared to the 2007 edition?
A: The 2017 reaffirmation did not introduce new technical requirements; it confirmed the 2007 edition as current. Minor editorial updates and reference corrections were made to align with the latest Canadian Electrical Code, Part I. The core safety test methods and performance criteria remain unchanged.
A: The 2017 reaffirmation did not introduce new technical requirements; it confirmed the 2007 edition as current. Minor editorial updates and reference corrections were made to align with the latest Canadian Electrical Code, Part I. The core safety test methods and performance criteria remain unchanged.