Aircraft Circuit Breakers, Toggle Switches and Sensitive Switches

Updated October 13, 2026

Types and where they are used

Start from the job: protect a wire, switch a circuit by hand, or sense a mechanical position. Each job has its own specification family, and several of the older military documents now point to SAE standards.

Ground support equipment and test consoles use many of the same parts as aircraft panels. If you are building a console or a cart, see our ground support equipment page for how the fabrication side is sourced.

The specifications and their status

Several aircraft breaker documents were cancelled by DoD and handed to SAE, so the number on an old drawing may not be the number you can buy against. The status below is what the cancellation notices and EverySpec listings say as of October 2026; confirm the current revision on ASSIST or SAE before release.

Both cancellation notices carry the same caution: the supersession information is valid as of the notice date and may itself be superseded by later revisions of the SAE document. SAE standards are sold by SAE, so budget for buying the current issue if your drawing still calls the MS or MIL number.

How the part numbers are built

Military switch and breaker part numbers are mostly the letter M, the specification sheet and a dash number, with the meaning carried by the sheet rather than the digits. MIL-PRF-8805G shows the pattern as M8805/XX-XXXX: designator, specification sheet number and a dash number formulated on that sheet. Switches formerly on MS sheets keep the original MS number unless a superseding M number has been assigned.

MIL-PRF-8805G also classifies every switch with codes that the sheets use to build the dash number. These are worth knowing because they tell you what a switch was qualified to:

MIL-PRF-55629E uses M, the sheet number and a sequential dash number for breakers with identical poles, and M, the sheet number and the pole ratings for breakers with mixed poles. MIL-DTL-3950 splits switches into three categories: Category I is completely defined by an MS standard or sheet and must come from the QPL; Category II differs only in minor details such as termination and must come from a source qualified on the similar Category I part; Category III is not covered by a sheet. Categories II and III are nonstandard and carry the manufacturer's part number.

Ratings, materials and the trade-offs

For breakers, the rating that matters is the combination of current, voltage, frequency and mounting. MIL-PRF-55629E covers single and multipole breakers from 0.2 to 100 amperes, at up to 240 volts 400 hertz, 480 volts 60 hertz and 125 volts dc, with panel seal mounts available from 0.2 through 50 amperes and auxiliary contacts for monitoring. Two cautions in its scope affect design and procurement:

• Mounting plane. Calibration is affected if the breaker is mounted in other than the vertical plane. A magnetic breaker bought for a tilted console face needs that discussed with the manufacturer.
• Pure tin. Designers are warned that these breakers may contain a pure tin finish on some component parts. Space and some missile programs prohibit pure tin, so the part may need a waiver or a different source.

For switches, the trade is between sealing, temperature and contact load. A MIL-PRF-8805 hermetic switch costs more than a resilient seal version but resists fluid and pressure ingress; a temperature code 3 or 4 part survives engine bay heat that a code 1 part will not. MIL-DTL-3950 qualification includes short circuit, salt spray, thermal shock, moisture resistance, sand and dust and switch sealing tests, and the specification references aviation turbine fuel (MIL-DTL-83133), turbine engine oil (MIL-PRF-7808) and dielectric coolant (MIL-PRF-87252) among its applicable documents, which tells you the fluids a qualified toggle is expected to meet. It also sets resistive, inductive and lamp load tests separately, so read the sheet for the load type you have.

Environmental qualification: DO-160 and MIL-STD-810

Component specifications qualify the part; DO-160 and MIL-STD-810 qualify the equipment it goes into. A breaker or switch qualified to its own specification has been tested with MIL-STD-202 methods for vibration, shock, salt spray and the rest, but that is not the same as the box passing DO-160.

• RTCA DO-160. RTCA Special Committee 135 describes DO-160 as defining minimum standard environmental test conditions and standardized procedures for airborne equipment environmental tests. Its September 2025 terms of reference state the document is at revision G, that EUROCAE ED-14 is technically identical, and that revision H was in work with publication planned for 2026. FAA Advisory Circular AC 21-16G is the FAA document that recognizes it. Confirm which revision your certification basis or customer invokes.
• MIL-STD-810. The current base document we found is MIL-STD-810H, Environmental Engineering Considerations and Laboratory Tests, dated 31 January 2019; check ASSIST for change notices. It is a test method standard written to be tailored to the item's expected environments, not a pass list.

In practice, buyers ask a supplier two questions: what the part itself is qualified to, with the report or QPL listing, and whether the manufacturer has data showing the part survived DO-160 or MIL-STD-810 levels in a representative unit. Treat the second as engineering evidence for your own qualification, not a substitute for it. Test lab capacity for unit level qualification is covered on our test lab time page.

Solid state power controllers, at a high level

A solid state power controller (SSPC) combines the switching job of a relay and the protection job of a breaker in semiconductor electronics, with electronic trip curves and status reporting to a controller. They are common in newer aircraft and spacecraft power distribution because they are remotely commanded and report faults.

For sourcing, the main point is that an SSPC is an electronic assembly, not an electromechanical part. It is usually bought to a manufacturer or program specification rather than a QPL, it contains semiconductors that fall under your EEE parts program, and it fits the DFARS 252.246-7008 definition of an electronic part, which includes circuit assemblies. Ask for the manufacturer's qualification report, radiation data for space use, and lot traceability for the internal parts. See EEE parts grades for how screening levels apply.

What to put on the purchase order

• Full part number as drawn. If the drawing calls MS3320 or MIL-C-5809, state whether the SAE AS33201 or AS58091 part is acceptable, since the military documents are cancelled.
• Specification and slash sheet with revision.
• QPL or QPD source for qualified parts, bought from the manufacturer or its authorized distributor; for MIL-DTL-3950 Category II, a source qualified on the similar Category I part.
• Lot or date code traceability on the certificate of conformance and the label.
• Finish restrictions such as no pure tin, no cadmium, and hexavalent chromium authorization status on DoD work.
• Mounting hardware, boots, guards and lock rings as separate lines if the drawing lists them.
• Qualification data or a QPL listing reference, and any DO-160 or MIL-STD-810 evidence you need for your own report.
• Packaging that protects actuators and terminals from bending.
• DFARS counterfeit clauses and prime flow-downs.

Counterfeit and quality risks, and how to receive them

Breakers and switches are relabeled more often than they are faked from scratch. The usual problems are a commercial switch marked with an M number, a breaker with the wrong rating sleeve or collar, a surplus part with corroded terminals, or an MS number substituted for a cancelled one without anyone checking the replacement standard. For DFARS purposes a plain breaker or switch is not named in the electronic parts definition, but an SSPC is; ask your contracts team how your program treats them. Our counterfeit parts avoidance guide covers the clauses.

At receiving:

• Compare the marking, rating and manufacturer code to the PO and the QPL listing for that sheet.
• Check the actuator travel, detents and lock features by hand; a toggle that feels gritty or loose has often been reworked or stored badly.
• Inspect terminals and threads for plating damage, corrosion and solder from prior use.
• Confirm breaker ratings on the button or collar match the label and certificate.
• Match lot or date codes across part, package and certificate.

See receiving inspection for the general dock routine.

How we source breakers and switches

We do not stock breakers or switches, publish prices or act as an authorized or franchised distributor for any manufacturer. We source the part numbers on your drawing through the manufacturer or its authorized and franchised distributors, confirm which superseding standard applies when a document has been cancelled, and flow your finish, data and traceability requirements down in writing.

• Breakers and switches kitted per panel, console or harness.
• Parts combined with panel machining, sheet metal enclosures and harness builds on one purchase order; see sheet metal fabrication.
• Cancelled MS numbers and out of production switches chased under counterfeit-avoidance controls; see obsolete aerospace parts.

Related parts: relays and contactors, sensors and transducers, motors and actuators, and the electromechanical overview.

Request breakers, switches or a panel kit

Send the part numbers, quantities, the drawing revision and whether SAE replacements for cancelled MS or MIL numbers are acceptable through the harness and electromechanical quote form. That answer decides which sources can quote. A person replies within one business day, and every order ships with a certificate of conformance. For controlled drawings, read how we handle files and controlled programs.

Questions

Related

• Hermetically Sealed Military Relays and Contactors
• Ground Support Equipment Fabrication for Launch and Spacecraft Programs
• How to Buy Obsolete Parts Without Buying Counterfeits
• Sourcing Obsolete Aerospace Parts Safely

Sources

• MIL-C-5809G Notice 1, cancellation, refers to SAE AS58091 (17 Mar 2005), EverySpec
• MS3320N Notice 2, cancellation, refers to SAE AS33201 (31 Aug 1999), EverySpec
• MIL-PRF-55629E, Circuit Breakers, Magnetic, Unsealed or Panel Seal, Trip-Free (10 Jun 2011), EverySpec
• EverySpec FSC 5925 index, Circuit Breakers (MIL-PRF-39019F listing)
• MIL-DTL-3950J w/Amendment 1, Switches, Toggle, Environmentally Sealed (12 Mar 2014), EverySpec
• MIL-PRF-8805G, Switches and Switch Assemblies, Sensitive, Snap Action (29 Feb 2016), EverySpec
• EverySpec FSC 5930 index, Switches (MIL-DTL-8834K, MIL-PRF-22885G, MIL-DTL-6807F listings)
• RTCA SC-135 Terms of Reference, DO-160 revision G and DO-160H plan (approved 25 Sep 2025)
• EverySpec MIL-STD-0800 to 0899 index, MIL-STD-810H (31 Jan 2019)
• Acquisition.gov, DFARS 252.246-7008 Sources of Electronic Parts