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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 13:15:00 +0200
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On 13-10-2024 01:33, Don Y wrote:
> On 10/12/2024 4:02 PM, Klaus Vestergaard Kragelund wrote:
>> On 12-10-2024 12:00, Don Y wrote:
>>> On 10/12/2024 2:38 AM, Klaus Vestergaard Kragelund wrote:
>>>> Somebody was talking about 48V warts. Some standards only allow 24V 
>>>> (for wet environments), and 32V for certain parts of the world
>>>
>>> 48V wall-warts/bricks are typically used in midspan PoE
>>> injectors (and as standalone power supplies for PDs
>>> without PSEs).  As such, almost always in dry locations.
>>>
>>> Can those "certain parts of the world" use PoE products
>>> with nominal 48VDC delivered over the twisted pairs?
>>> Is the limit on the "packaging" or on the potential?
>>
>> In IEC60730 (safety for household products), 2.1.5 SELV is defined as 
>> maximum 42V. Note states that for the US and Canada the SELV voltage 
>> is max 30VRMS (which equates to 42.4Vpeak). Those numbers are when 
>> dry, when wet it reduces to 15V/21.2V peak.
>>
>> Normally things are dry, so US is 30V. I do not know how it is 
>> possible to allow 48V warts.
>>
>> Searching a little, it seems the 48V systems are approved against 
>> telecommunication standards which may not use the SELV nomenclature
>>
>> NEC has higher voltages, up to 60VDC, but matters little since most 
>> product needs to comply to 60730/60950, and now 62368 has replaced 60950.
>>
>> The touch voltages are defined in yet another standard, IEC61201. I do 
>> not have access to that one.
>>
>> The 48V warts are also strange in that when the product is tested for 
>> peak SELV voltage a single fault must be introduced. So if you mess 
>> with the feedback of the SMPS, the trip voltage determines the maximum 
>> voltage, and that is most likely significantly higher than 48V.
> 
> But, is the constraint on the "wall wart package"?  Or, on the presence
> of ~48V on conductors that are accessible to the user?

POE voltage is directly on the pins of the ethernet interface. The 
designer insources the external wart with 48V nominal voltage (which can 
be more under single fault)

There may be a loop hole

If you ship the adapter/wart with the product you should test as a 
system, right?

But if you just state it needs 48V in, you can blame the wart 
manufacturer if it puts out more voltage.

> 
> E.g., an N-port PoE switch looks like the (output) power cords from
> N 48V wall warts.  (technically, this is only the case while the
> cables are physically connected to their PDs as the PSE should
> power down the unconnected port).
> 
> Because the switch "isn't a wall wart", is it exempt?
> 
> Or, is all this moot because PoE switches aren't "household kit"?
> 

I just took a random POE ethernet switch which uses a 54V external adapter:

https://www.proshop.dk/Switch/Netgear-GS110TPv3-8-Port-Gigabit-PoE-Ethernet-Smart-Switch-with-2-SFP-Ports-and-Cloud-Management/2871263

No mention of standards in the datasheet. But found a reference in the 
hardware manual:

https://www.downloads.netgear.com/files/GDC/GS108Tv3/GS108Tv3_GS110TPv3_GS110TPP_HIG_EN.pdf

Page 2, link to netgears compliance document:

https://www.netgear.com/about/regulatory/

Then searched for the model no in the Declaration of conformance:

https://kb.netgear.com/11621/EU-Declarations-of-Conformity?article=11621

Finally here:

https://www.downloads.netgear.com/files/DoC/204-11529-04_CE_GS110TPv3_EN-EP-FR-IT-GR-SP_19SEP22.pdf?_ga=2.171448224.1872638720.1728816211-1033670545.1728816210

Mentions use of 60950 and 62368

I am doing EMC tests tomorrow at a test-house, so will ask them whats 
the deal ;-)