Hi Glyn,
I understand that there should not be hazard in all expected situations
(normal / abnormal use and fault condition) and USB cable is too short
to consider transients.
What I am trying to do is to understand 62368-1 and reading it I came to
5.4.11 that was hard for me to understand what are exact listed there
requirements and if they touch my devices.
That laptop I described is an example of device that looks as being not
excluded from 5.4.11, and USB is looking (for me) as being external
circuits according to 62368-1 definition of this therm and being
indicated in table 14.
The only way to solve this laptop problem, I see, is if we have to
assume that the note in table 14 of not considering transients (as USB
is wholly in the same building) makes USB being not indicated in table.
When first time writing my question I was not sure if I can assume this.
Now I suppose that I have to assume this (if transients are not taken
into account than cable is not indicated in table 14).
The device I have in mind is 12V powered access controller hawing RS485
(not isolated) and because of this RS485 I am trying to understand 5.4.11.
Now I suppose that:
1. It is permanently connected equipment so 5.4.11 not apply, and even
it is not permanently connected (as being isolated from Mains by 12V
supply) then
2. RS485 as being whole in one building (transients are not taken into
account) is not indicated in table 14 so 5.4.11 not apply.
The typical 12V supply used (MEAN WELL DRC-40A) specification says:
SAFETY STANDARDS: UL60950-1, TUV EN60950-1 approved
WITHSTAND VOLTAGE: I/P-O/P:3KVAC I/P-FG:2KVAC O/P-FG:0.5KVAC
I always assumed that it is better to not Earth DC12V (its negative pole).
Reading 62368-2 5.4.11 description I confirm myself in this belief. Not
Earthing 12V we not provide (by RS485) Earth potential to a remote
environment making it being still save even if by any other fault the
Mains potential can be there.
Do you agree with me?
Best Regards
Piotr Galka
W dniu 2024-05-10 o 17:26, Glyn Payne pisze:
Hi Piotr,
Maximum USB cable lengths are quite short, a few meters, and they are
not designed to be part of the ‘building or structure’, hence
transients are not considered for these ports. If a USB extender or
hub is used to extend the USB and this is wired through the building
or structure then transients would be the problem of the hub
manufacturer and not your product.
There was/is /IEC 62368-//3/: /Safety aspects for DC power
transfer through communication cables and ports/, which is
referenced by IEC 62368-1 however this being reworked by TC108 and
as far as I can tell few people are using it in it’s present form.
When testing your product under 62368-1 the test house will
determine the maximum voltage and current the USB (or serial) port
can provide, under normal, abnormal and fault conditions, to
ensure that there is no hazard.
Best regards,
Glyn Payne
*From:*Piotr Galka <piotr.ga...@micromade.pl>
*Sent:* Wednesday, May 8, 2024 9:28 PM
*To:* EMC-PSTC@LISTSERV.IEEE.ORG
*Subject:* Re: [PSES] IEC 62368-1: To understand chapter 5.4.11
You don't often get email from piotr.ga...@micromade.pl. Learn why
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Hi Bostjan,
I know that if circuit is not going out of building it is considered
being without transients. My doubt is mainly because in 5.4.11 says
about circuits being external and indicated in table 14 and according
to my understanding 3.3.1.1 USB was external and note about transients
in table 14 for me didn't make for me USB being not indicated in table.
In my RS485 design even it is in one building I assume during storm up
to 50V temporary difference between several grounding points and I use
2 steps protection. I know of two such incidents that after lightning
struck directly into the building, many systems stopped working, but
ours did.
I acknowledge that USB is not external circuit.
Thanks a lot.
I have never bought any standard abroad and as I have written
answering to Johns post I see that 62368-2 is not in current Polish
Standard Committee offer.
Best regards
Piotr Galka
W dniu 2024-05-08 o 18:45, Boštjan Glavič pisze:
Hi Piotr
If circuit does not go out of building it is not considered as
circuit with transients. I think you should check other standard
like IEC 62151 and IEC 62102 which clasify external circuits.
From my experiences, and I do have quite some, USB is not
considered as external circuit in the sense of clause, where
requirements between external circuit and PE are specified.
Did you also check 62368-2?
Best regards
Bostjan
Poslano iz Outlook za Android <https://aka.ms/AAb9ysg>
------------------------------------------------------------------------
*Od:* Piotr Galka <piotr.ga...@micromade.pl>
<mailto:piotr.ga...@micromade.pl>
*Poslano:* sreda, maj 8, 2024 5:21:33 PM
*Za:* EMC-PSTC@LISTSERV.IEEE.ORG <EMC-PSTC@LISTSERV.IEEE.ORG>
<mailto:EMC-PSTC@LISTSERV.IEEE.ORG>
*Zadeva:* Re: [PSES] IEC 62368-1: To understand chapter 5.4.11
Hi Bostjan,
Thanks for your feedback, but...
I am slowly and carefully reading 62368-1 for the first time.
It defines 'external circuit' in 3.3.1.1 as "electrical circuit
that is
external to the equipment and is not mains".
I assumed one device = one equipment so I thought laptop is an
equipment. After your post I checked how equipment is defined in
62368-1
but in 3.3 there is no equipment definition so I don't know what is
equipment.
May be USB device (pendrive) connected without cable to laptop can be
assumed being its part, or even device powered by USB (mouse,
keyboard)
can be assumed being its part, but USB can be used to connect other
equipment, I think. Do laser printer being powered separately from
mains
connected to laptop is understood as being internal part of
equipment?
Laptop is probably manufactured by someone else than laser
printer. They
can't assume they manufacture single equipment, I think.
In past I have read about USB being used to connect active wifi
antenna
located on the roof (with few hubs to extend connection length).
Having
all that in mind it is hard for me to accept that for 62368-1 USB is
equipment internal circuit.
Now.
If we assume laptop with connected to it mouse, external keyboard and
printer is one equipment then going to my field: do the access
control
controller with RFID readers connected to it by RS485 is also one
equipment (all powered from one 12V supply, and located in one
building)
making RS485 connection being internal equipment circuit?
I don't think so.
And I repeat my main question regarding 5.4.11: Do the access
controller
permanently connected to 12V supply that is permanently connected to
mains is permanently connected equipment? I think yes. Even 12V
supply
has isolation in it.
If I change understanding of equipment and assume that controller
+ 12V
supply are one equipment than thinks get easier - such understood
equipment is permanently connected. But is it one equipment if
controller is manufactured by someone other then 12V supply.
Best regards
Piotr Galka
W dniu 2024-05-07 o 19:49, Boštjan Glavič pisze:
> Hi Piotr
>
> USB circuit is internal circuit. There are no transients
expected on USB. Clause 5.4.11 is not applicable for power supply
with USB output.
>
> Paired conductor is a telecommunication network that we had in
old times (analogue network, ISDN,...).
>
> I hope this helps. If you need more info, you can contact me.
>
> Best regards,
> Boštjan
>
>
>
> -----Original Message-----
> From: Piotr Galka <piotr.ga...@micromade.pl>
<mailto:piotr.ga...@micromade.pl>
> Sent: Tuesday, May 7, 2024 5:40 PM
> To: EMC-PSTC@LISTSERV.IEEE.ORG
> Subject: [PSES] IEC 62368-1: To understand chapter 5.4.11
>
> CAUTION: This email originated from outside of our organisation.
Do not click links or open attachments unless you recognise the
sender and know the content is safe.
>
>
> Trying to understand 62368-1...
>
> I have got laptop with type A power supply so it looks being not
excluded from 5.4.11 by rules in 5.4.11.1.
> For me USB are external circuits indicated in Table 14, ID
numbers 1 and
> 2 (I think USB is 'Paired conductor', but even not it certainly
is 'Any other conductors').
> The note in Table 14 about not taking into account transients
for external circuits installed wholly within the same building is
only about transients so I think it doesn't make USB being not
indicated in table.
> USB cable can be used to connect laptop to printer and in
printer USB can be earthed, I think.
> Dos this means that according to first sentence of 5.4.11.2 each
USB port in this laptop should be separated from its other USB ports?
> I don't believe there is such requirement.
>
> My real problem to understand is as follows:
> Typical access controller have several not separated from each
other inputs (several RFID reader inputs, door state control
input, tamper inputs and others).
> I need to understand if the access controller powered from
(external to
> it) 12V DC buffered (= having accu in it) supply is permanently
connected equipment or not?
> To disconnect it from 12V supply you need tools, to disconnect
12V supply from mains you need tools, but 12V supply has isolation
in it so access controller is not electrically connected to mains
and 3.3.3.4 says about needing tools to disconnect from mains (if
something is not connected than tools are not needed to make it
being disconnected, I think).
> Being permanently connected equipment is the easiest way for
controller to be excluded from 5.4.11.
> But if it is not permanently connected than its inputs are in
the same situation as laptop USB ports I described first as more
common to everyone.
>
> What I miss or wrongly understand?
>
> Regards
> Piotr Galka
>
> P.S.
> Last month free time I spend browsing about 2800 EMC-PSTC posts
collected by my mail program for few years.
>
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