Square D B103 B Series Thermal...
IN STOCK (leaves warehouse same day if ordered before 3pm ET)
$12.69
Square D B103 B Series Thermal Overload Unit, Melting Alloy, Class 20

Square D B103 B Series Thermal Overload Unit, Melting Alloy, Class 20

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Model: B103

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

$12.69
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Square D B Series Thermal Overload Unit, Melting Alloy

The Square D B Series Thermal Overload Unit is a Type S / Type B melting-alloy thermal overload element engineered for use with compatible Square D overload relays in motor starter applications. Rated Class 20 for motor tripping and suited for motor circuits up to 600V maximum, this family of thermal units spans 30 models — B103 through B910 — so contractors, panel builders, and OEMs can match the exact heater rating required for a given motor full-load amperage. Every model in the B Series shares the same melting-alloy thermal design, Class 20 tripping characteristic, and 600V maximum rating, with individual catalog numbers differentiating the amperage range each unit is designed to protect. The line is available in standard, quick, and slow trip versions to fit a range of motor-starting and duty-cycle requirements.

Key Features

  • Thermal Overload Type: Melting alloy design for dependable, repeatable Class 20 motor tripping shared across every model in the range.
  • Motor Tripping Class: Class 20 tripping characteristic suited for standard motor duty on all 30 B Series models.
  • Series: B range of thermal units, offered in 30 catalog numbers (B103, B128, B130, B140, B145, B155, B167, B175, B188, B195, B220, B240, B265, B280, B320, B330, B360, B370, B400, B415, B450, B500, B550, B560, B620, B700, B770, B820, B880, B910) for use with compatible Square D overload relays.
  • Voltage Rating: 600V maximum rating for motor circuit protection, shared by the entire B Series line.
  • Trip Speed Options: Thermal units available in standard, quick, and slow trip configurations to match motor starting characteristics.
  • Broad Compatibility: Switches electric motors with a variety of overload relays across NEMA Sizes 00-7.
  • Simple Ordering: Straightforward catalog numbering across the B103-B910 range for fast selection and replacement.

Technical Specifications

  • Warranty: 18 months
  • Warranty Period: 18 months
  • Range Of Product: B
  • Motor Tripping Class: 20
  • Country of Origin: Mexico

Typical Applications

  • Motor Overload Protection in Motor Starters
  • Commercial and Industrial Electrical Installations
  • Motor Control Centers and Control Panels
  • OEM Control Panel Building
  • Replacement Thermal Units for Existing Square D Overload Relays

Why Square D?

Square D thermal overload units use proven melting-alloy technology to deliver consistent Class 20 tripping performance, helping protect motors in commercial and industrial systems. With a straightforward catalog numbering system spanning the full B103-B910 range and broad compatibility across NEMA Sizes 00-7 overload relays, these thermal units make it easy for contractors, panel builders, and OEMs to source dependable motor protection components backed by an 18-month warranty.

Manufacturer Resources

Product Specs

Product Type:
Thermal Overload Unit
Series:
B
Voltage Rating:
600V
Configuration:
Melting Alloy
Country of Origin:
Mexico
Department:
Electrical
Product Group:
Motor Control & Automation
Product Material:
Melting Alloy
Grade:
Class 20
Product Subgroup:
Overload Relays

Square D B103 – Frequently Asked Questions

1) How do I pick the right Square D B thermal unit number for my motor?
The catalog number on a Square D B Series thermal unit is not the motor amps directly. You size it from the motor's full load amps and the specific overload relay or starter you are installing it in, using Square D's thermal unit selection table for that relay. Order by the exact number once you have it: the B range runs from B1.30 up through B88.0, with 30 catalog numbers in between such as B2.40, B12.8, B32.0 and B62.0.
2) Will a Square D B thermal unit fit my overload relay, or do I need a different type?
B Series thermal units are Type B melting alloy elements made to drop into Square D overload relays used on NEMA Size 00 through 7 starters. If your relay takes a different Square D thermal unit family, the B element will not seat correctly. Match the family called out on the relay's thermal unit chart before ordering.
3) Is a Class 20 overload the right trip class for my motor, or do I need Class 10?
The B Series units are Class 20, meaning they allow a longer acceleration time before tripping than a Class 10 element. That suits standard motor duty and higher inertia loads like fans, compressors and conveyors. Motors with a short permissible locked rotor time, or submersible and hermetic motors that the nameplate says need Class 10, should not be protected with a Class 20 element.
4) Can I use a B Series thermal unit as a direct replacement in an existing Square D starter?
That is the most common use for these. If the old element is stamped with a B number, order the same B number and it goes back in the same relay. Only change the number if the motor itself changed or the original was sized wrong, and then re-size from the relay's thermal unit table rather than guessing up a size.
5) What does melting alloy mean on a Square D thermal overload unit, and does it reset?
Melting alloy is the eutectic solder pot design: sustained overload current heats the element, the alloy softens, a ratchet wheel turns and the relay contacts open. It is a manual reset device, so the starter stays tripped until somebody presses the reset. That is what you want on a motor where an unattended automatic restart is a hazard.
6) Does a thermal overload unit replace the fuse or breaker in a motor circuit?
No. The B Series thermal unit is the overload element only, protecting the motor against sustained running overcurrent. Short circuit and ground fault protection still has to come from the branch circuit fuse or breaker ahead of the starter. Both are required on a motor branch circuit.
7) Are the B thermal units available in quick trip or slow trip versions?
Square D lists the B range thermal units in standard, quick and slow trip configurations so the element can be matched to how the load accelerates. The trip speed is part of the catalog number you order, so specify it along with the numeric rating.
8) Where are Square D B Series thermal overload units made?
Mexico is the country of origin on the B Series thermal units. Useful if you are filling out a submittal or a domestic preference form on a public job.
How fast can I get the Square D B103 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 Square D B103 come with a warranty?
Absolutely. The Square D B103 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 Square D B103?
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 Square D B103 from ZenSupply?
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