You may also like
Mersen J166 Class J Fuse Reducer, 600V AC/DC, 200kA SCCR
The Mersen J166 Class J Fuse Reducer provides professional-grade electrical protection engineered for Class J fuse holders, with a 600V AC/DC voltage rating and 200kA SCCR (short circuit current rating) for high-energy fault protection. This UL Listed and CSA Certified fuse reducer also supports 250V and 600V Class H, K, and R applications, making it a versatile choice for demanding industrial and commercial electrical systems that require dependable, code-compliant overcurrent protection components sized for Class J fuse compatibility.
Key Features
- Dual Voltage Rating: 600V AC/DC capability supports both alternating and direct current applications for maximum installation flexibility across a wide range of electrical systems.
- 200kA SCCR: High short circuit current rating delivers superior interrupting capacity and fault protection in high-energy electrical distribution systems where fault currents can be substantial.
- Class J Fuse Compatibility: Engineered specifically for Class J fuses, ensuring proper fit and reliable electrical performance in compatible fuse holders and disconnect assemblies.
- Multiple Standards Support: Also compatible with 250V and 600V Class H, K, and R fuse applications for versatile installation options in mixed-fuse-class panels.
- Professional-Grade Construction: Mersen engineering delivers dependable, durable performance in demanding electrical environments requiring long-term reliability.
Certifications & Compliance
- UL Listed, Guide No. IZZR, File E105670
- CSA Certified 6225-01 207417
Technical Specifications
- Class: J
- Ac Voltage: 600 VAC
- Dc Voltage: 600 VDC
- Sccr: 200 kA
- Ul Certification: E105670 IZZR.E105670
- Csa Certification: 6225-01 207417
- Standards: 250V and 600V Class H, K, and R - UL Listed Guide No. IZZR, CSA Certified. 600V Class J - UL Listed
Typical Applications
- Industrial Motor Control Centers
- Commercial Electrical Distribution Panels
- Manufacturing Facility Power Systems
- Data Center Electrical Infrastructure
- Healthcare Facility Critical Power
- Educational Institution Electrical Systems
- Municipal and Government Buildings
Why Mersen?
Mersen fuse reducers combine decades of electrical protection expertise with rigorous UL Listed and CSA Certified testing standards. The 600V AC/DC rating and 200kA SCCR give electrical professionals confidence in code-compliant, reliable fault protection for high-energy Class J fuse installations across industrial, commercial, and institutional facilities.
Manufacturer Resources
Mersen Product Catalog
Product Specs
- Ac Voltage:
- 600 VAC
- Ce Conformity:
- Consult Technical Services
- Class:
- J
- Csa Certification:
- 6225-01 207417
- Dc Voltage:
- 600 VDC
- Lead Free:
- Consult Technical Services
- Rohs Compliant:
- Consult Technical Services
- Sccr:
- 200 kA
- Ul Certification:
- E105670 IZZR.E105670
- Department:
- Electrical
- Product Group:
- Circuit Protection
- Product Type:
- Fuse Reducer
- Product Subgroup:
- Fuse Holders & Blocks
Mersen J166 – Frequently Asked Questions
1) What does a Class J fuse reducer actually do in a disconnect?
A fuse reducer like the Mersen J166 lets you install a smaller amp-rated fuse in a fuse clip or holder built for a larger one. You drop the reducer into the existing clips, then the smaller fuse seats into the reducer. It's how you right-size overcurrent protection to a motor or feeder without swapping the disconnect or fuse block. The J166 is built for Class J holders and is rated 600V AC and 600V DC.
2) Can the Mersen J166 fuse reducer be used on DC circuits, not just AC?
Yes. The J166 carries a 600 VDC rating alongside its 600 VAC rating, so it can be used in DC distribution as well as standard AC panels. That matters for drives, battery rooms, and DC bus work where a lot of AC-only accessories are not acceptable.
3) Will a fuse reducer lower the short circuit current rating of my fused disconnect?
Not with the J166. It carries a 200 kA SCCR, which matches or exceeds the interrupting rating of the Class J fuses normally used with it, so the reducer is not the limiting element in a high fault current service. Spec engineers on motor control centers and service entrance gear usually need that number in writing, and 200 kA is what this one holds.
4) Is the Mersen J166 fuse reducer UL Listed and CSA approved for an inspected commercial job?
Both. It's UL Listed under file E105670, guide IZZR, and CSA Certified under 6225-01 207417. Those are the file numbers to hand an AHJ or put on a submittal for healthcare, government, or education work where listed components are required throughout the assembly.
5) I have Class R fuse clips, not Class J. Can I still use this Mersen reducer?
The J166 is not a Class J only part. Mersen lists it as supporting 250V and 600V Class H, K, and R applications in addition to 600V Class J, so it covers mixed-fuse-class panels where you're dealing with older H/K clips or Class R rejection clips. The Class J listing is the 600V one.
6) I need a reducer for a 600V Class J holder in a motor control center - does the Littelfuse LRUR work or should I use the Mersen J166?
Go with the Mersen J166 for a Class J holder. It is specified as Class J and rated 600 VAC / 600 VDC with a 200 kA short circuit current rating, which is what an MCC bucket or high fault current distribution panel is typically specified against. The Littelfuse LRUR Series is described as a fuse clip adapter by series rather than by fuse class, so for a Class J opening the J166 is the direct match.
7) What part number do I order for the Mersen Class J fuse reducer?
Order it as Mersen J166. That's the manufacturer part number, and it's a single-model item, so there are no finish, size, or handing options to specify on the order.
8) Do fuse reducers come in pairs, or do I need one per fuse?
Reducers are sized per fuse end, so a single fuse needs a set at both ends and a three-phase disconnect needs enough sets to cover all three poles. Count the poles and the fuse ends before you order the J166 rather than ordering one piece per fuse.
9) What is the difference between the Mersen J166 and the Littelfuse LRUR fuse clip adapter?
Both are fuse reducers that adapt existing clips to a smaller fuse. The Mersen J166 is the one with published electrical ratings here: 600V AC/DC and 200 kA SCCR, UL Listed and CSA Certified. The Littelfuse alternative is the LRUR Series (also catalogued as LRU2 Series). If your submittal requires stated voltage and SCCR numbers, the J166 is the one that carries them.
10) Is a fuse reducer the right fix, or should I just change the fuse block?
Use a reducer when the disconnect or fuse block is already installed and correctly rated, and the only thing wrong is that the fuse amp rating you need is smaller than the clips. That's the J166's job, and at 600V AC/DC with a 200 kA SCCR it won't derate the assembly. Replace the block instead when you're changing fuse class for a rejection requirement the reducer doesn't cover, or when the block itself is damaged or under-rated for the system voltage.
11) What is an alternative to the Mersen J166 fuse reducer for adapting fuse clips?
The Littelfuse LRUR Series (also catalogued as the LRU2 Series) is a fuse clip adapter style reducer that serves the same basic purpose of fitting a smaller fuse into a larger fuse clip. The Mersen J166 is specified for Class J fuse holders and is rated 600 VAC and 600 VDC with a 200 kA SCCR, and it is UL Listed under file E105670, guide IZZR, and CSA Certified under 6225-01 207417. If your panel work requires those specific ratings documented on the part, the J166 is the one carrying them.
12) Do I need to confirm RoHS or lead-free status on the Mersen J166 before specifying it?
For RoHS, CE conformity, and lead-free status, Mersen directs those questions to its Technical Services group rather than publishing a blanket declaration on the J166. If your project has a material compliance requirement, get that confirmation in writing before it goes on the submittal. The electrical ratings and the UL/CSA listings are documented.
13) Is a fuse clip adapter the same thing as a fuse reducer?
They do the same job of letting a smaller ampere-rated fuse sit in a holder built for a larger one - the Littelfuse LRUR Series is described as a fuse clip adapter and the Mersen J166 as a fuse reducer. What differs is how each is specified: the J166 is called out by fuse class and electrical rating, Class J at 600 VAC and 600 VDC with 200 kA SCCR, while the LRUR is identified by series. Match the part to the holder you actually have rather than assuming the two are interchangeable.
How fast can I get the Mersen J166 delivered?
Most orders ship the same day from our distribution partners, with quick delivery throughout the
continental
U.S.
Need it urgently? Contact Us for expedited shipping options.
Can I return it if it doesn’t work for me?
Yes—ZenSupply offers a hassle-free return policy. If the product isn’t the right fit,
reach out to our support team for a return authorization or setup a return by following our return instructions.
Does the Mersen J166 come with a warranty?
Absolutely. The Mersen J166 is backed by a manufacturer’s warranty.
For full warranty terms, check the product documentation or Contact Us.
How do I get technical support or installation help for the Mersen J166?
You can call, text, or email our expert support team for fast answers. We’re here to help with
product
selection,
installation tips, and troubleshooting. Contact Us
Why buy the Mersen J166 from ZenSupply?
ZenSupply makes it easy to get the commercial door hardware you need—fast shipping, expert support,
and
rewards on
every order.
Our team is always ready to help you choose the right product for your project.