FCC Rules for Kits and Subassemblies

FCC Rules for Kits and Subassemblies

EMC FastPass AdminUncategorized 27 Comments

This article is an extract from the eBook “Global Certifications for Makers and Hardware Startups“, available for sale here.


I’m often asked whether electronics ‘kits’, where the kit is a group of parts assembled by the end user can be exempted from the rules. This post explores that idea.

The FCC defines a kit as (FCC 15.3):

“Any number of electronic parts, usually provided with a schematic diagram or printed circuit board, which, when assembled in accordance with instructions, results in a device subject to the regulations in this part, even if additional parts of any type are required to complete assembly.”

Based on the definition above, it looks clear that non-authorized kits that are intended to form a complete product when fully constructed are technically not legally permitted to be sold in the US. That is because if you are marketing and selling a kit to an end user, which the user will then build into a full product, there is no reason to suspect that the normal rules would not apply. Kits would have the same, if not more (because extra human error is introduced) chance of being non-compliant with the radiated and conducted emissions limits. It just doesn’t make logical sense that kits would be excluded from FCC emissions rules.

The same is true of intentional radiator kits (i.e. products with a transmitter that are subject to certification). In response to the question “What are the FCC Rules for building and marketing of kits of products, which when completed are subject to the FCC Rules?”, the FCC replied quite clearly in KDB927445 that “As described in Section 15.23, individuals are permitted to construct a device for personal use without seeking equipment authorization from the Commission, but it may not be marketed as a kit. All other devices subject to Certification (whether marketed as a Kit or not), must be certified under Subpart J of Part 2.”

I would point out that there is a distinction between a kit that when assembled will form a “subassembly” and a kit that will form a full device that will be subject to normal FCC authorization procedures. Kits that form subassemblies will be discussed separately below this section. Here I am only discussing kits that are intended to form a full product once the end user puts the pieces together.

How do some companies get away without certifying their devices?

You may be asking yourself how companies such as Sparkfun, a business based on selling electronics kits and wireless development kit companies continue to sell large numbers of non FCC authorized kits, with seeming impunity. For Sparkfun, the rules that apply in most cases relate to “subassemblies”. This just means that Sparkfun’s customers will most likely use the products to build larger products containing a number of subassemblies. For example, that may include an Arduino™ processor board along with several sensors or peripherals and an LCD. The user may even put all of these parts into an enclosure. If the user sells this product containing multiple subassembly parts in an enclosure, for all intents and purposes they are now a “manufacturer” and their equipment is subject to the normal FCC authorization procedures.

It’s worth noting that before integrating a subassembly into their system, many manufacturers will demand to see proof of compliance of the subassembly. That’s because they don’t want your subassembly to be the cause of a failure of the whole system. Subassemblies that have poor emissions or immunity performance can easily cause a larger system to fail regulatory testing, so it’s in their best interests to demand proof of compliance, even if it isn’t a legal requirement.

When does the FCC consider you to be a manufacturer?

Where is the FCC’s line in the sand for when home built equipment becomes subject to their rules? That is defined in Part 15.23.

“Equipment authorization is not required for devices that are not marketed, are not constructed from a kit and are built in quantities of five or less for personal use.”

That’s probably easier to understand if I say it in the opposite way; If you are marketing your product (are you putting out ads, or offering your product for sale?) or it is not intended for personal use (i.e. it’s for someone else) or if you make more than 5 of them, then you need to have your device tested according to FCC rules. If you do any of these things, the FCC views you as a manufacturer.


Keeping your device within the scope of “subassembly” definition is one of the best chances you have of avoiding FCC (and CE) authorization requirements.

The exemption goes as follows (FCC 15.101):

“No authorization is required for a peripheral device or a subassembly that is sold to an equipment manufacturer for further fabrication; that manufacturer is responsible for obtaining the necessary authorization prior to further marketing to a vendor or to a user.

Subassemblies to digital devices are not subject to the technical standards in this part unless they are marketed as part of a system in which case the resulting system must comply with the applicable regulations. Subassemblies include:

(1) Devices that are enclosed solely within the enclosure housing the digital device, except for: power supplies used in personal computers; devices included under the definition of a peripheral device in §15.3(r); and personal computer CPU boards, as defined in §15.3(bb);

(2) CPU boards, as defined in §15.3(bb), other than those used in personal computers, that are marketed without an enclosure or power supply; and

(3) Switching power supplies that are separately marketed and are solely for use internal to a device other than a personal computer.”

If you can keep your device within that definition, then you can probably get away without FCC testing. It would be up to the manufacturer that uses your “subassembly” in their own product to have their product tested.

FCC Caveat:

“Responsible parties should note that equipment containing more than one device are not exempt from the technical standards in this part unless all of the devices in the equipment meet the criteria for exemption. If only one of the included devices qualifies for exemption, the remainder of the equipment must comply with any applicable regulations. If a device performs more than one function and all of those functions do not meet the criteria for exemption, the device does not qualify for inclusion under the exemptions.” For example, if you have a device with a wireless transmitter and some baseband circuitry that happens to be exempt, the wireless transmitter still has to be tested.


Hopefully this article clears up the FCC rules on authorization for kits and subassemblies. If you have any more questions about your specific device, contact an accredited FCC test lab.

Andy Eadie is a former senior hardware design engineer and former EMC test lab owner. He’s had a weird fascination with magnets since 4 years old and has been publishing articles, eBooks and online courses since he founded EMC FastPass in 2014.
Andy Eadie is a former senior hardware design engineer and former EMC test lab owner. He’s had a weird fascination with magnets since 4 years old and has been publishing articles, eBooks and online courses since he founded EMC FastPass in 2014.
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Comments 27

  1. I find the article verry clear and interesting. However I have a smal remark regarding subasemblies. If somone produces subasemblies like PSU’s and those are not tested for FCC or even CE and a manufacturer uses that PSU in his final product only to find that his product does not pass FCC (or CE) because of that particular PSU unless he has to do costly modifications to his product then I think it is reasonable to expect some testing from subasemblies so an manufacturer can be at ease his purchased subasembly wil not cause havoc in his final product.

    Kind regards

    1. Post

      Hi Hendrik. Totally agree with you.. I’ll modify the article to make it clear that manufacturers who design subassemblies into their system may require proof of compliance of the subassemblies anyway, regardless of whether it’s legally necessary. Thanks for your input.

  2. Hi Andy, the article gives a good overview about the FCC procedure. The FCC rules are very similar to the rules in the automotive world (compare ECE R10). This document consider also electronic sub-assemblies (ESA) and complete vehicles. There are two possibility: You can check the EMC behavior of each ESA or of the vehicle. In each case the vehicle manufacturer is responsible for the el/mag properties of the car. But the limits and requirements of the ECE R10 are too low, so it is very easy to fulfill the requirements.
    Kind regards Hans-Joerg

    1. Post
    1. if i understand it right – you have to –
      the idea behind that could be that if you are making more than five you have a ‘small’ series and it could be that from this ‘pool’ there are some that escape your private ‘area’ – or that if you make so many that they build in sum a ‘to big’ system…
      (thats are just my ideas…)

      sunny greetings

  3. Hi Andy,

    Thanks for the overview! Maybe this is or short answer or your topic for your next post… But what are the chances or history of the FCC taking action against non-emitters?

    For example there are many Kickstarter projects the are sold clearly in violation of these rules, yet searching the FCC records there are very few cases against intentional radiators. I could find none against non-emitters.

    As an artist/designer with limited technical background, this has been an inimidating factor in moving forward with my ~100 piece art project!


    1. Post
    1. Post

      Thanks Rick. I see from your email you’re on Maui you lucky guy. Just had a holiday to Hawaii (Oahu) and I’m looking forward to going back already! How’s your tech sector on the islands?

  4. Hey Andy!

    This is a great article, thanks for posting it. Regarding exemption 1 for Subassemblies: “Devices that are enclosed solely within the enclosure housing the digital device…”
    Does that mean that if I wanted my dev kit to pass as subassembly, I would not have to be offering it within a plastic enclosure?

    Thanks again

    1. Hi Mario, I think the key section is, “that is sold to an equipment manufacturer for further fabrication; that manufacturer is responsible for obtaining the necessary authorization prior to further marketing to a vendor or to a user”.

      So I read that to mean whether your device has an enclosure or not, it is considered a subassembly if you’re selling it to someone who will use it for further fabrication (into a larger product/system). Give an accredited lab a call for your particular product.

  5. Andy,
    Very nice article. Do you have a clear understanding of how the FCC views devices subject to different parts combined in a larger product? For example, if I make a portable information kiosk, and it includes a PWM motor and controller (Part 15) to animate a big waving cardboard hand, and a fluorescent light (Part 18) to illuminate some advertising, is it considered a Part 18 or Part 15 product – the most important sub-question being should it have the Part 18 label or not?

  6. Hi Andy,

    Great article. What happens if I have a kit for a hobbyist (a Bluetooth garage door opener), that fully falls within the description of a kit, but I choose to NOT include in the kit for sale one of the components (the Bluetooth module), and instruct the user to purchase it separately on e-bay for instance. Could my kit then be considered a subassembly? (as it requires further fabrication by the end user), and then be exempt for testing?

  7. Wonderful Article. What about Packaging Raspberry Pi which is FCC certified, in an enclosure. Does it need to be FCC tested again?

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