Mersen USM Series UltraSafe Mi...
IN STOCK (leaves warehouse same day if ordered before 3pm ET)
$58.36
Mersen USM Series UltraSafe Midget Fuse Holder, DIN Rail Mount

Mersen USM Series UltraSafe Midget Fuse Holder, DIN Rail Mount

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Model: USM1

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

$58.36
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Mersen USM Series UltraSafe Modular Fuse Holder, Midget Class, IP20 Finger-Safe

The Mersen USM Series UltraSafe modular fuse holder is engineered for Midget 1-1/2" x 13/32" AC and DC-rated fuses up to 30A, delivering a new level of panel-building safety. Rated 800VAC and 1000VDC, this polyamide-bodied holder qualifies as "Finger-Safe" under IEC and DIN standards to an IP20 grade of protection, including fuse changing with the flick of a finger. Available in 1, 2, 3 or 4-pole configurations with optional visual blown-fuse indicators, UltraSafe holders snap onto standard 35mm DIN-rail and save up to 15% mounting space versus conventional fuse holders.

Key Features

  • Fuse Compatibility: Sized for Midget Class 1-1/2" x 13/32" fuses, with this configuration built for a 4-pole, 30A maximum arrangement.
  • Durable Construction: Tough, durable polyamide body material offers exceptional insulating properties for reliable long-term performance.
  • Clip-In Fuse Installation: Pressure-plate wiring connections and clip-in fuse installation simplify fuse changes and field wiring alike.
  • Electrical Rating: Rated 800VAC / 1000VDC at 50/60 Hz with a 100 kA short circuit current rating (SCCR) for AC or DC applications.
  • Wiring Range: Accepts #6 to #14 AWG solid or stranded conductors, tightened to a 15 lb-in torque rating.
  • IP20 Finger-Safe Protection: Qualifies as Finger-Safe under IEC and DIN standards to an IP20 grade, protecting installers during fuse changing.
  • DIN-Rail Mounting: Snaps onto standard 35mm DIN-rail, and multipole units can be field-assembled using pin-tie handles for space-saving panel layouts.

Certifications & Compliance

  • RoHS Compliant
  • Finger-Safe to IP20 under IEC and DIN Standards

Technical Specifications

  • ROHS Compliant: Yes
  • Torque Rating: 15 lb-in
  • Ampere Rating: 30 A
  • Frequency: 50/60 Hz
  • Rated Voltage AC UL: 800 V
  • Rated Voltage DC UL: 1000 V
  • Number of Poles: 4-Pole
  • Wiring Range: #6 to #14 Solid or Stranded
  • SCCR: 100 kA
  • Installation Mounting: DIN Rail
  • Fuse Installation Method: Clip-in
  • Body/Insulating Material: Polyamide

Typical Applications

  • Motor Control and Power Distribution Panels
  • DIN-Rail Panel Building
  • Industrial and Commercial Control Panels
  • AC/DC Circuit Protection Requiring Finger-Safe Access
  • Midget Fuse Retrofit and Panel Space Optimization

Why Mersen?

Mersen's USM Series UltraSafe fuse holder combines a durable, RoHS-compliant polyamide body with IP20 Finger-Safe protection to keep panel builders and maintenance electricians safer during fuse changes. With an 800VAC / 1000VDC rating, 100 kA SCCR, and space-saving DIN-rail mounting, it delivers dependable, code-conscious circuit protection for demanding industrial and commercial control panel applications.

Manufacturer Resources

Product Specs

Product Group:
Wiring Devices
Ampere Rating:
30 A
Torque Rating:
15 lb-in
Installation Mounting:
DIN Rail
Fuse Class:
Midget
Fuse Installation Method:
Clip-in
Max Fuse Rating:
30 A
Department:
Electrical
Product Type:
Fuse Holder

Mersen USM1 – Frequently Asked Questions

1) Will the Mersen USM fuse holder mount on my existing 35mm DIN rail?
Yes. The USM snaps directly onto standard 35mm DIN rail, no adapter or mounting plate needed. Mersen states it saves up to 15% of mounting space compared to conventional fuse holders, which is the reason most panel builders pick it when a backplane is already crowded.
2) Can I use the Mersen USM holder on a DC circuit, like a solar or battery panel?
Yes. It's rated 1000VDC as well as 800VAC at 50/60 Hz, with a 100 kA short circuit current rating on either AC or DC. Just make sure the Midget fuse you drop in is itself DC-rated for your system voltage, since the holder rating is a ceiling, not a substitute for the fuse rating.
3) How do I pick between 1, 2, 3 and 4-pole on the Mersen USM holder?
Pole count matches the number of ungrounded conductors you're protecting. USM1 for a single-pole DC leg or one phase of a control circuit, USM2 for a two-wire DC circuit or single-phase line and neutral protection, USM3 for a three-phase feed, USM4 for three-phase plus a neutral or a fourth protected leg. Multipole units also field-assemble from singles using pin-tie handles, so you aren't locked into one configuration if the panel changes.
4) What wire size will the Mersen USM terminals accept, and what torque do I set?
Terminals take #6 through #14 AWG, solid or stranded, on pressure-plate connections. Torque them to 15 lb-in. That's a low number, so use an inch-pound driver rather than guessing, and re-check after the first thermal cycle if the panel runs warm.
5) Is the Mersen USM fuse holder safe to change a fuse on with the panel live?
It's built for that situation. The USM qualifies as Finger-Safe under IEC and DIN standards to IP20, including during fuse changing, so live parts stay shielded from an accidental finger contact. The fuse pops out and clips back in by hand. That said, IP20 finger protection is not a substitute for your site's arc flash and lockout procedures.
6) Can I use the Mersen USM holder for a 125V plug fuse branch circuit application?
No. The Mersen USM UltraSafe holder takes Midget class 1-1/2 x 13/32 cartridge fuses up to 30A and is rated 800VAC and 1000VDC with a 100 kA SCCR for control panel work. Plug fuses are a different fuse body entirely and will not clip into it. For a 125V 15A plug fuse application, the Littelfuse LSRY series plug fuse box cover unit is the device built for that fuse type. Confirm the fuse body style before ordering either one, since the holders are not interchangeable.
7) I need fuse protection on a cord run outside the panel, not on a DIN rail. What should I use instead of the Mersen USM holder?
The Mersen USM UltraSafe holder is a DIN rail mount device sized for Midget class 1-1/2 x 13/32 fuses, so it belongs inside a panel or enclosure on 35mm rail. For a fused connection made in-line on a cable run in a wet or washdown location, the Littelfuse WPB1 series is an in-line watertight fuse holder instead of a rail-mounted one. The two solve different problems: the USM gives you clip-in fuse changes and pressure-plate terminals accepting #6 to #14 AWG inside a control panel, while the WPB1 is built to be spliced into a conductor run.
8) Does the Mersen USM come with a blown fuse indicator?
Blown-fuse visual indicators are an option on the UltraSafe USM line rather than standard on every holder. If you want a maintenance electrician to spot the open fuse from across the panel without pulling carriers one by one, specify the indicating version when you order.
9) I need a watertight in-line fuse holder, not a DIN rail one. What should I look at instead?
The Mersen USM is a panel-mount product; it snaps to 35mm DIN rail inside an enclosure and offers IP20 finger protection, which is not a weather or washdown rating. For an in-line run outside a panel, look at the Littelfuse WPB1 Series in-line watertight fuse holder instead.
10) For a multi-pole DC circuit in a control panel, is there a simpler alternative to the 4-pole Mersen USM4?
Within the UltraSafe Midget line the alternatives are the same holder in fewer poles: USM1, USM2 and USM3 cover 1, 2 and 3 pole arrangements with identical 30A, 800VAC and 1000VDC ratings, clip-in fuse loading and 35mm DIN rail mounting, so you can size the pole count to the circuit rather than buying a 4-pole and leaving a pole idle. Multipole units can also be field-assembled using pin-tie handles. The Littelfuse LSRY plug fuse box cover unit and WPB1 in-line watertight holder are different form factors and do not offer a DIN rail multi-pole equivalent.
11) What's the USM holder body made of, and will it hold up in a hot panel?
The body is polyamide, chosen for its insulating properties and durability over long service. It's also RoHS compliant, which matters if you're building panels for export or for a customer with a materials declaration requirement in the spec.
How fast can I get the Mersen USM1 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 USM1 come with a warranty?
Absolutely. The Mersen USM1 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 USM1?
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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