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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