Re: EMC compliance question

On Sun, 13 Oct 2024 01:02:13 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> 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.

Single-fault abnormals look at steady state results - an overvoltage
protection that prevents a continuous hazard (ie latching OVP) is
sufficient.

RL