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From: Klaus Vestergaard Kragelund <klauskvik@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: EMC compliance question
Date: Sat, 12 Oct 2024 11:38:30 +0200
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On 12-10-2024 01:31, legg wrote:
> On Thu, 10 Oct 2024 14:11:35 -0700, john larkin <jl@glen--canyon.com>
> wrote:
> 
>> On Thu, 10 Oct 2024 13:41:07 -0700, Don Y
>> <blockedofcourse@foo.invalid> wrote:
>>
>>> On 10/9/2024 4:03 PM, bitrex wrote:
>>>> What's the deal with the "CPU board" exemption?
>>>>
>>>> "CPU board. A circuit board that contains a microprocessor, or frequency
>>>> determining circuitry for the microprocessor, the primary function of which is
>>>> to execute user-provided programming, but not including:
>>>> A circuit board that contains only a microprocessor intended to operate under
>>>> the primary control or instruction of a microprocessor external to such a
>>>> circuit board; or
>>>> A circuit board that is a dedicated controller for a storage or input/output
>>>> device."
>>>>
>>>> So if one sells a board that has say a PIC on it and some support logic, and
>>>> the 9kHz+ signals are all internal to the uP (self-clock), but it's otherwise a
>>>> functionally complete design other than it's not in a housing, is that an
>>>> exempt product?
>>>
>>> Who is your customer?  If you are selling it as a *product*,
>>> it is not a *compliant* product so your customer inherits
>>> no certifications (because there are none).
>>>
>>> If your customer integrates it into *his* product, then
>>> the responsibility for "product certification" falls on him
>>> (so, you have saved *yourself* a few pennies on the certification
>>> process and left him with any "problems" that your board may
>>> pose to *his* certification).
>>
>> A few pennies for a certified test lab to do full certs?
>>
>>>
>>> If you are selling to hobbyists, you *may* be able to get by
>>> as a noncompliant product (the first case, above) -- so long
>>> as none of your (few?) customers finds themselves drawing
>>> the ire of neighbors, etc. when your device interferes with
>>> their pursuit of life, liberty and happiness.
>>>
>>> But, you are still exposed as the seller of that noncompliant
>>> product.  How likely will your customers "have your back"
>>> if things get sticky?
>>>
>>> In the latter case, your customer (integrator) will *likely*
>>> be thankful for any steps you have taken to certify your
>>> "component" as he goes about looking for certification on
>>> *his* composite system.
>>>
>>> Why do you think so many products are sold with El Cheapo,
>>> off-brand wall warts instead of taking the power supply
>>> design *into* the overall product?
>>
>> A wart relieves one of all the AC-line safety certifications. There
>> are some big warts these days, including 48v ones.
>>
>> One can resell a cheap wart with the usual molded-in (usually fake)
>> UN/CE/CSA markings, or let the customer buy their own wart.
>>
> 
> A wart used in an EMC certification becomes part of it. Hence
> mrfs listing and retailing part numbers for suitable use.
> 
> Warts can be (and are) listed independently, to reduce
> potential testing and deployment gliches. A listed
> wart doesn't guarantee radiated compliance, only facilitates
> conducted performance on that one, main, port.

All of the EMC tests still needs to be done even if you use a wart.
But LVD (safety) becomes a lot easier, if it's below 15W consumption (no 
glow-wire test etc)

Somebody was talking about 48V warts. Some standards only allow 24V (for 
wet environments), and 32V for certain parts of the world