Fuse Tools

Technical Reference Tool

Motor Circuit Protection Selector

Look up fuse sizing, disconnect, NEMA starter, wire AWG, and conduit for motor branch circuits. Sourced from Bussmann motor circuit protection tables aligned with NEC Article 430.

NEC Tables: 430.147–430.150 NEC Article: 430.52 Source: Bussmann SPD Section 12

Reference tool — verify before installing. Always confirm selections against the current National Electrical Code, motor nameplate data, controller manufacturer's overload tables, and local codes. Specific installation conditions may require different sizing. This tool is not a substitute for professional engineering judgment.

Full coverage. 11 voltage/phase combinations covered: Three-Phase 200V, 208V, 230V, 460V, 575V · Single-Phase 115V, 230V · DC 90V, 120V, 180V, 240V. Source: Bussmann SPD Section 12 / NEC Article 430.

1 Motor Type

Results

Fuse Sizing Options

Click any amp → Eaton product page

Fuse Type	Optimal Best protection	Max Gen. NEC general apps	Max Heavy High inrush

Supporting Circuit

Code minimums

Optimal Protection

Best short-circuit protection with backup overload protection (RK5/RK1 dual-element fuses). Smaller fuse, smaller disconnect possible.

Max General

NEC 430.52 maximum for general-purpose motor branch circuit protection. Requires properly-sized overload device.

Max Heavy Start

NEC 430.52(C)(1) Exception No. 2. Use when motor has long starting time, jogging duty, or high inrush.

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Our technical team can confirm this selection for your job

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Reference Chart

Fuse Cross-Reference

Translate fuse catalog numbers between Mersen, Bussmann, Littelfuse, and Edison. Type any part number, class, or description into the search box — or browse the full chart below.

Manufacturers: Mersen · Bussmann · Littelfuse · Edison Coverage: Class CC, RK, J, L, T, G, Midget, Semiconductor

Verify before substituting. Cross-referenced fuses share form factor and electrical class but may differ in specific characteristics (interrupting rating, time-current curves, certifications). Always check the datasheet for your application before swapping brands.

Can't find what you need?

Call us — we can cross any fuse, even if it's not on this chart

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Mechanical Reference

European Fuse Dimensions

Form factors, body sizes, and dimensions for European fuse types. Useful when servicing imported equipment, sizing fuse holders, or identifying unfamiliar fuses on industrial machinery.

Standards: IEC 60269, DIN Voltage Range: 250V — 1300V Form Factors: 5 families

Dimensions are nominal. Always verify exact dimensions against the specific manufacturer's datasheet before ordering fuse holders, busbars, or panel cutouts. Tolerances vary by manufacturer.

Need to identify a specific fuse?

Bring it in — we'll measure it and find the replacement

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Control Transformer Reference

Transformer Fuse Sizing

Primary and secondary fuse sizes for single-phase industrial control transformers, shown as actual Bussmann or Mersen catalog numbers. Pick a side, pick a manufacturer, then click any part number to open it on the manufacturer's website.

Primary: Bussmann FNQ-R · Mersen ATQR (Class CC time-delay) Secondary: Bussmann FNM · Mersen TRM (midget time-delay) Source: Acme Electric (Hubbell) control transformer selection charts · NEC 450.3(B)

Reference tool — verify before installing. Sizes come from the Acme Electric control transformer selection charts. Confirm against your transformer's nameplate and documentation, NEC 450.3(B) and 430.72(C), the controller manufacturer's requirements, and local codes. Other transformer brands may publish different values.

Transformer side

Manufacturer

Transformer VA Primary voltage

No exact catalog rating; showing the next size down (hover for details) 300% band 167% band 125% band Show NEC bands

How to use it

Find the transformer's VA rating in the left column and its primary (line) or secondary (control) voltage across the top. The cell where they meet is the fuse. Click the part number to open that exact fuse on Eaton.com or Mersen.com.

Primary fuses are sized for Class CC time-delay fuses, the basis of the Acme chart. Bussmann's own guidance: use FNQ-R on control transformer primaries and do not upgrade to LP-CC.

When a size isn't made

The chart gives decimal amps (e.g. 0.6 A = 6/10 A). Some chart values (such as 1.9, 3.8, or 5.5 A) aren't catalog ratings. When that happens, the tool shows the closest rating below the chart value, never above it, and marks the cell with an amber dot. The detail card shows the next size up so you can make the call.

Midget secondary fuses (FNM / TRM) stop at 30 A. Chart values above 30 A are greyed out.

The NEC bands

NEC 450.3(B) sets the maximum fuse as a percentage of the transformer's rated current (VA ÷ V). Primary: 300% under 2 A, 167% from 2 to 9 A, 125% at 9 A and above. Secondary: 167% under 9 A, 125% at 9 A and above. The shaded bands and step lines show where each rule applies, calculated from each cell's VA and voltage.

Need a hand?

Send us the transformer nameplate and we'll quote the fuses and fuse blocks

(708) 756-5600

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Fuse Tools

Motor Circuit Protection Selector

Fuse Cross-Reference

European Fuse Dimensions

Transformer Fuse Sizing

How to use it

When a size isn't made

The NEC bands

Address