Mersen A4J Series Class J Fast...
IN STOCK (leaves warehouse same day if ordered before 3pm ET)
$140.77
Mersen A4J Series Class J Fast-Acting Current-Limiting Fuse

Mersen A4J Series Class J Fast-Acting Current-Limiting Fuse

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Model: A4J50

In Stock (leaves warehouse same day if ordered before 3pm ET)

$140.77
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Mersen A4J Series Class J Fast-Acting Current-Limiting Fuse

Mersen's A4J Series Class J fast-acting fuses deliver excellent current-limiting protection for a wide variety of industrial and commercial electrical applications, with ratings available up to 250A. Rated 600VAC and 300VDC (UL) with a 200 kA AC maximum interrupting capacity, these Amp-Trap® fuses feature unique dimensions that prevent substitution with fuses carrying lower voltage ratings, interrupting ratings, or current-limiting capability. This A4J family is offered with a choice of termination style — Blade or Ferrule — so the correct connection type can be matched to the fuse block or holder in use, while every option shares the same Class J construction, voltage ratings, and interrupting rating. Clip-mounted for standard Class J fuse holders and rated for 50/60 Hz AC/DC operation, the A4J Series protects circuits without compromising system safety.

Key Features

  • Fuse Class: Class J construction delivers compact, high-performance current-limiting protection for demanding circuits.
  • Speed/Characteristic: Fast-Acting response provides rapid clearing of short-circuit currents to limit downstream damage.
  • Voltage Ratings: Rated 600VAC and 300VDC (UL) for reliable use in both AC and DC circuit applications.
  • Amperage: Amp-Trap® A4J fuses are available including a 250A rating for demanding load protection.
  • Interrupting Capacity: 200 kA AC maximum interrupting rating (I1) suits high fault-current environments.
  • Termination Options: Available in Blade or Ferrule connection styles to match your application's fuse block or holder.
  • Mounting: Clip-mount design provides compatibility with standard Class J fuse blocks and holders.
  • Frequency: Rated for 50/60 Hz operation across supported circuits.
  • Unique Rejection Dimensions: Prevents substitution with fuses of lower voltage, interrupting, or current-limiting ratings.

Certifications & Compliance

  • RoHS Compliant

Technical Specifications

  • ROHS Compliant: Yes
  • Mounting: Clip
  • AC Max I.R./Breaking Capacity (I1): 200 kA
  • Frequency: 50/60 Hz
  • Rated Voltage AC (UL): 600V
  • Rated Voltage DC (UL): 300V
  • AC or DC: AC/DC
  • Fuse Class: Class J
  • Packaging: 1 EA
  • Termination Options: Blade, Ferrule

Typical Applications

  • Branch Circuit Overcurrent Protection
  • Motor and Feeder Circuit Protection
  • Industrial Control Panels and Switchboards
  • Commercial and Industrial Electrical Distribution Systems
  • Current-Limiting Protection for Critical and Sensitive Loads

Why Mersen?

Mersen's Amp-Trap® A4J Series fuses combine Class J construction with a 200 kA interrupting rating and RoHS-compliant materials to deliver dependable, code-compliant overcurrent protection. Available with Blade or Ferrule terminations, the family lets electricians and panel builders select the connection style that fits their equipment while retaining the same voltage, interrupting, and current-limiting performance. Unique rejection dimensions help ensure only correctly rated fuses are installed, supporting safe, reliable performance in demanding electrical systems. Trust Mersen for current-limiting fuse protection engineered for professional electrical applications.

Manufacturer Resources

Mersen Product Catalog

Product Specs

Mounting Method:
Clip
AC Max I.R./Breaking Capacity: I1:
200 kA
ROHS Compliant:
Yes
Frequency (Hz):
50/60 Hz
Rated voltage AC UL:
600 V
Speed/Characteristic:
Fast-Acting
AC or DC:
AC/DC
Rated voltage DC UL:
300 V
Fuse Class:
Class J
list_batch:
MERSEN-20260825
Department:
Electrical
Product Group:
Circuit Protection
Product Type:
Fuse
Series:
A4J
Voltage Rating:
600V
Amperage Rating:
250A
Standards:
RoHS Compliant
Product Subgroup:
Fuses

Mersen A4J50 – Frequently Asked Questions

1) Will a Mersen A4J fuse fit my existing Class R or Class CC fuse block?
No. The A4J is a Class J fuse and Class J bodies use their own rejection dimensions, so they will not drop into Class R or Class CC clips. The A4J is clip-mounted for standard Class J blocks and holders only. Those rejection dimensions are deliberate: they stop anyone substituting a fuse with a lower voltage, interrupting, or current-limiting rating into a Class J holder. If your block is Class CC, you need a Class CC fuse such as the Littelfuse CCMR Series instead.
2) Should I order the blade or ferrule version of the A4J fuse?
That is decided by your fuse block, not by performance. The A4J comes in two termination styles, Blade and Ferrule, and both share the same Class J construction, 600VAC/300VDC ratings and 200 kA interrupting rating. Ferrule ends are the lower-amp style (the ferrule option here is the A4J50) and blade ends carry the higher ratings (A4J250). Match the end style to the clips or bolted terminals already in the holder.
3) Can I use the Mersen A4J on a DC circuit?
Yes, within limits. The A4J is rated AC/DC, with a UL AC rating of 600V and a UL DC rating of 300V. So a 480V or 600V AC panel is fine, but on DC you must stay at or below 300V. A 600V DC bus is outside this fuse's rating.
4) Is a 200 kA interrupting rating enough for my service with high available fault current?
The A4J carries a 200 kA AC maximum interrupting rating (I1), which is the top tier commonly specified for industrial switchboards and control panels. If your short-circuit study shows available fault current at or below 200 kA at the fuse location, the A4J covers it, and its current-limiting action reduces the let-through energy reaching downstream equipment.
5) What is the difference between the Mersen A4J and a Littelfuse BLF midget fuse for control panel protection?
Both are fast-acting, but they are built for different circuits. The Littelfuse BLF is a midget fast-acting fuse in a laminated tube rated 250V. The Mersen A4J is a Class J fast-acting fuse rated 600VAC and 300VDC with a 200 kA AC interrupting rating, available with blade or ferrule terminations and clip-mounted in standard Class J blocks. If the control circuit is 250V and uses midget holders, the BLF is the match. If the panel is a 600V branch, feeder or motor circuit with high available fault current, the A4J is the one sized for it.
6) What amperage ratings does the Mersen A4J fuse go up to?
The A4J family runs up to 250A, and that top 250A rating is the blade-terminated A4J250. The ferrule style covers the smaller end of the range, for example the 50A A4J50. Pick the amperage from your overcurrent calculation, then take whichever termination that rating comes in.
7) Can I standardize my facility's fuse stock on the Mersen A4J instead of several glass and midget fuses?
Only for the circuits it is rated for. The A4J is a 600VAC, 300VDC Class J fuse for branch circuit, feeder and panel protection in industrial and commercial distribution. It does not replace low-voltage control and automotive-style links, which is where parts like the Littelfuse AGU and AGA glass tube fuses or the 250V Littelfuse BLF midget fast-acting fuse live. Standardize the Class J blocks on A4J, and keep the low-voltage links separate.
8) My panel needs a time-delay fuse for motor starting - is the Mersen A4J the right choice?
The Mersen A4J is a fast-acting fuse, built to clear short-circuit current quickly and limit let-through energy, which suits feeders and sensitive loads more than circuits with heavy inrush. Where the equipment uses Class CC blocks and the load needs a time-delay curve to ride through motor starting, the Littelfuse CCMR Series is a Class CC time-delay fuse, offered in ratings such as the 40A CCMR040. Match the fuse class to the block already in the panel - Class J and Class CC bodies are not interchangeable.
9) I need replacement fuses for a PowerLogic energy meter - will a Mersen A4J work?
No, those are separate items. Square D sells a PowerLogic energy meter fuse pack as a set of three rated 0.5A at 600V, sized for metering voltage inputs. The Mersen A4J is a Class J power fuse with ratings up to 250A, clip-mounted in Class J blocks and used for branch, feeder and motor circuit protection. Order the PowerLogic fuse pack for the meter's own inputs and the A4J for the Class J fuse block feeding the equipment.
10) Will the A4J work on 50 Hz equipment for an export panel build?
Yes. The A4J is rated for 50/60 Hz operation, so the same part works in a 60 Hz domestic panel and a 50 Hz export build. It is also RoHS compliant, which matters on panels shipping into markets that require it.
11) Does the Mersen A4J ship individually or in a multi-pack?
Packaging is 1 each, so quantity ordered equals fuses received. Worth noting if you are stocking three-phase spares, which take three per set. For comparison, the Square D PowerLogic energy meter fuse pack is sold as a set of three 0.5A 600V fuses.
How fast can I get the Mersen A4J50 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 A4J50 come with a warranty?
Absolutely. The Mersen A4J50 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 A4J50?
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
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