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From: Klaus Vestergaard Kragelund <klauskvik@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: EMC compliance question
Date: Sun, 13 Oct 2024 21:34:46 +0200
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On 13-10-2024 17:56, legg wrote:
> On Sat, 12 Oct 2024 13:11:02 -0400, Joe Gwinn <joegwinn@comcast.net>
> wrote:
> 
>> On Sat, 12 Oct 2024 11:38:30 +0200, Klaus Vestergaard Kragelund
>> <klauskvik@hotmail.com> wrote:
>>
>>> 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
>>
>> In these certain parts of the world, what do they use for telephones?
>> The standard central office batteries were and still are 48 Vdc. Which
>> is why the electrical codes in the US and EU ignore anything below 50
>> Volts or so.
>>
>> Only very recently are cellphones taking over.
>>
>> Joe Gwinn
> 
> Telecom standards tend to mirror BellCore regs.
> 
And thinking about that, the ringing voltage was close to 100Vrms, and 
using flimsy connectors. Amazing that was legal