Very good advice. There is a 'dumb' fallback, if your best efforts to
find a documented rationale to not apply the requirement, is to consider
how much extra it costs to comply with it, compared to the cost of
trying to find a reason not to comply with it.
For example, I found that replacing the inter-winding insulation in a
transformer by PET tape, which has a very high dielectric strength, met
the requirement that I considered unnecessary by a very large margin,
and incidentally was marginally less costly.
======================================================================================
Best wishes John Woodgate OOO-Own Opinions Only
www.woodjohn.uk
Rayleigh, Essex UK
I hear, and I forget. I see, and I remember. I do, and I understand.
Xunzi (340 - 245 BC)
On 2022-12-02 19:15, Joe Randolph wrote:
Hi Steve:
I work mostly with the 60950-1 and 62368-1 standards for ITE, so I’m
not familiar with the details of the requirements in 61010-1.
That being said, I’ve seen many cases where someone misinterpreted the
creepage/clearance/dielectric requirements in 60950-1 and 62368-1, not
realizing that their specific configuration was exempt from those
requirements. So, I’d like to have more details on the specific
requirement that concern you, and the specific circuit where you are
trying to apply this requirement.
Is the 100 Vdc secondary fully floating with respect to the ground at
the AC mains, or is it referenced to the AC mains ground?
Does the AC mains connection use an ordinary “Pluggable Type A” plug
or is it hardwired?
If it uses a Type A plug, does that plug have a ground pin?
These are just some of the factors that can affect how the isolation
requirements apply to this specific design.
If the AC mains ground is obtained from a grounded Type A plug, there
is a fault scenario that */might/* be behind the requirement that
concerns you. This is case where the presumed ground in the AC outlet
is missing, or the user has installed a “cheater adapter” to convert
the 3-prong plug to a 2-prong plug.
In this case the ground node in the equipment becomes a floating node,
which creates certain potential scenarios that might create the need
for the requirement that concerns you.
I agree with you that it’s best to always make sure that understand
the rationale behind any requirement that is giving you trouble. Once
you know the rationale, you will better understand whether the
requirement should apply to your specific application.
Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com <mailto:j...@randolph-telecom.com>
http://www.randolph-telecom.com <http://www.randolph-telecom.com/>
*From:*Steve Brody [mailto:sgbr...@comcast.net]
*Sent:* Thursday, December 1, 2022 3:51 PM
*To:* EMC-PSTC@LISTSERV.IEEE.ORG
*Subject:* [PSES] Secondary creepage/clearance
I have a client who has a secondary pwb that has traces and vias that
may have 100 vdc on them adjacent to ground.
Per 61010-1 there is a requirement for spacing and/or dielectric test,
both depending on what the mains voltage is.
The question is why is the mains voltage a consideration or concern if
the 100vdc secondary voltage is several layers of impedance and
circuitry from the mains?
Is it a concern that a surge on the mains would trickle down to the
secondary circuit, or is there another reason/rationale?
I suggested that a dielectric test per Table 6 [in A1] would suffice
and put the issue to rest for this product, but the question from the
designers remains as to why is it a concern in the standard of what
the mains voltage is.
Is there anything in the standard, that I haven't found, that does not
require Table 6 to be followed if there is no way for a mains surge to
impact the secondary voltage?
I look to the experts for an explanation.
Thanks,
Steve Brody
sgbr...@comcast.net
C - 603 617 9116
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