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CAN CSA C22.2 No. 4248.8-18: Technical Specifications for Class H and K Fuses
A Comprehensive Review of Requirements for Non‑Renewable and Renewable Fuse Installations under the Canadian Electrical Code
The CSA C22.2 No. 4248 series establishes uniform requirements for fuses and fuseholders used in Canada. Part 8 of this series, CAN CSA C22.2 No. 4248.8-18, specifically addresses Class H (non‑renewable) and Class K (renewable) fuses rated up to 600 V AC and 200 kA interrupting capacity. This article provides an in‑depth overview of the standard’s scope, critical technical requirements, and compliance notes for engineers, inspectors, and maintenance personnel.
1. Scope and Purpose
CAN CSA C22.2 No. 4248.8-18 applies to Class H and K fuses and their associated fuseholders, intended for use in accordance with the Canadian Electrical Code (CEC), Part I. Class H fuses are non‑renewable (one‑time) overcurrent protective devices, while Class K fuses are renewable devices that allow the replacement of the fuse link after operation. The standard covers:
- Fuses rated up to 600 A, voltages up to 600 V AC;
- Fuseholders designed to accept these fuses;
- Requirements for mechanical interchangeability and environmental limits.
The primary objective of the standard is to ensure safe and reliable operation under normal and fault conditions, as well as dimensional uniformity so that fuses from different manufacturers can be properly installed in any compliant holder.
CSA Marking: Fuses and fuseholders that comply with 4248.8-18 may bear the CSA certification mark, indicating acceptance for use in Canada per the CEC and confirming that the product has passed all mandatory tests.
2. Technical Requirements
2.1 Classification and Ratings
Fuses covered by 4248.8-18 are classified by their interrupting rating, voltage, ampere rating, and whether they are renewable or non‑renewable. Class H fuses have a minimum interrupting rating of 10 kA symmetrical (rms). Class K fuses meet a minimum of 10 kA, but can be rated up to 200 kA when tested to the optional high‑interrupting tests of the standard. All devices must withstand their rated voltage and the mechanical stresses imposed during switching or fault interruption.
Table 1 summarizes the ampere ratings, voltage classes, and typical interrupting ratings specified in the standard.
| Fuse Class | Voltage (V AC) | Ampere Range (A) | Interrupting Rating (kA Sym) |
|---|---|---|---|
| H (non‑renewable) | 125 / 250 / 600 | 0–30 | 10 |
| H (non‑renewable) | 250 / 600 | 31–600 | 10 |
| K (renewable) | 125 / 250 / 600 | 0–30 | 10 (higher optional) |
| K (renewable) | 250 / 600 | 31–600 | 10 (higher optional) |
2.2 Construction and Dimensions
The standard defines precise dimensional envelopes for fuse cartridges and the matching fuseholder contacts. These requirements ensure that any Class H fuse can be directly replaced by another Class H fuse from a different manufacturer and that Class K replacement links fit properly. Critical parameters include:
- Overall length and diameter of the fuse body;
- Contact blade dimensions (thickness, width, and spacing);
- Terminal connection provisions for fuseholders.
Table 2 lists representative dimensional values for the most common ratings.
| Ampere Rating (A) | Voltage (V) | Body Diameter | Overall Length | Contact Type |
|---|---|---|---|---|
| 30 | 250 | 13.5 | 38.1 | Blade |
| 60 | 250 | 22.2 | 57.2 | Blade |
| 100 | 250 | 28.6 | 76.2 | Blade |
| 30 | 600 | 19.0 | 50.8 | Blade |
| 60 | 600 | 25.4 | 76.2 | Blade |
Installation Tip: Always verify that the fuseholder contact clips are not damaged or corroded before inserting a new fuse. Even a small dimensional deviation can cause excessive heating or arcing.
2.3 Performance Tests
Manufacturers must subject their products to a series of type tests to demonstrate compliance. The key performance tests required by 4248.8-18 include:
- Temperature rise test: The temperature of any external part shall not exceed specified limits when the fuse carries its rated current;
- Overload test: The fuse must clear overloads within defined time‑current curves;
- Short‑circuit interruption test: The fuse and holder must safely interrupt fault currents up to their rated interrupting rating;
- Endurance test: For fuseholders, repeated insertion and removal of fuses must not degrade electrical or mechanical performance.
The standard also requires that renewable fuses undergo a replacement link test to verify that a new link, when properly installed, provides the same performance as the original.
Critical Warning: Never substitute a non‑renewable (Class H) fuse with a renewable (Class K) fuse unless the entire assembly has been evaluated and listed for that purpose. Mismatched fuses can lead to unsafe operation and void certifications.
3. Implementation and Certification
Manufacturers seeking CSA certification for Class H or K fuses must follow the requirements of CAN CSA C22.2 No. 4248.8-18 in conjunction with the general part (Part 1) of the 4248 series. The certification process includes:
- Submission of product samples for testing by an accredited laboratory;
- Factory inspection and follow‑up audits;
- Marking with the CSA monogram and the relevant rating information.
Fuses that meet the standard are considered acceptable for installation under the CEC, provided they are used within their marked ratings and in circuits that do not exceed the specified interrupting capacity.
Caution – Fault Current Coordination: When using Class K fuses with optional higher interrupting ratings, the system available fault current must be properly calculated. Installing a fuse with a higher interrupting rating than necessary is permissible, but never install a fuse with a lower interrupting rating than the system’s available fault current.
4. Compliance and Application Notes
To ensure ongoing compliance, the standard mandates periodic follow‑up inspection of production. Changes in materials or manufacturing processes may require retesting. For end‑users, the following points are noteworthy:
- Always replace a fuse with one of the same Class, ampere rating, voltage rating, and interrupting rating;
- Use only fuseholders listed with the fuse to maintain the system’s short‑circuit rating;
- Conduct visual inspections regularly—signs of overheating or mechanical deformation indicate a problem that should be investigated.
Frequently Asked Questions
Q: What is the difference between Class H and Class K fuses?
A: Class H fuses are non‑renewable (one‑time) devices with a standard interrupting rating of 10 kA. Class K fuses are renewable—they permit replacement of the fusible link after operation—and can be designed for interrupting ratings up to 200 kA when tested to the optional requirements of the standard.
A: Class H fuses are non‑renewable (one‑time) devices with a standard interrupting rating of 10 kA. Class K fuses are renewable—they permit replacement of the fusible link after operation—and can be designed for interrupting ratings up to 200 kA when tested to the optional requirements of the standard.
Q: Are fuseholders included in the scope of 4248.8-18?
A: Yes. The standard covers fuseholders intended to accept Class H and K cartridge fuses. It specifies dimensional, temperature rise, and mechanical strength requirements to ensure proper fit and safe operation.
A: Yes. The standard covers fuseholders intended to accept Class H and K cartridge fuses. It specifies dimensional, temperature rise, and mechanical strength requirements to ensure proper fit and safe operation.
Q: Does compliance with 4248.8-18 automatically satisfy the Canadian Electrical Code?
A: Generally, yes. Fuses and fuseholders that bear the CSA mark per CAN CSA C22.2 No. 4248.8-18 are recognized as complying with the CEC, provided they are installed according to the manufacturer’s instructions and the applicable CEC rules (e.g., Section 14).
A: Generally, yes. Fuses and fuseholders that bear the CSA mark per CAN CSA C22.2 No. 4248.8-18 are recognized as complying with the CEC, provided they are installed according to the manufacturer’s instructions and the applicable CEC rules (e.g., Section 14).
Q: Can a Class H fuse be replaced with a Class K fuse of the same rating?
A: Only if the fuseholder is specifically listed for both Classes. The dimensional interface is compatible, but the renewable design of Class K fuses may require additional clearance or rejection features. Always check the holder’s marking and listings before substitution.
A: Only if the fuseholder is specifically listed for both Classes. The dimensional interface is compatible, but the renewable design of Class K fuses may require additional clearance or rejection features. Always check the holder’s marking and listings before substitution.
Technical article published 2026. This document is for informational purposes only and should not replace the full text of CAN CSA C22.2 No. 4248.8-18. For certification and compliance decisions, always refer to the latest edition of the standard and consult a qualified professional.