Re: [PSES] Secondary creepage/clearance

[Douglas Powell]

I've had personal experience with lightning coupled transients to the
secondary, strong enough to burn out an office Mr Coffee pot.
Interestingly, if you have a transformer in the coupling path and the
windings are oriented to normally invert a sine wave, the transient will
likely not be inverted.  This is because the coupling is
through inter-winding capacitance and not the transformer core flux. This
can usually be simulated with the IEC 61000-4-5 test as well.

-Doug

Laporte, Colorado USA
doug...@gmail.com
LinkedIn 

(UTC -07:00) Mountain Time (US-MST)




On Fri, Dec 2, 2022 at 3:17 PM Richard Nute  wrote:

>
>
>
>
> Hi Steve:
>
>
>
> Mains circuits are subject to lightning and switching transients both
> line-to-neutral and line/neutral-to-ground.  The transients are normal; to
> prevent insulation breakdown and consequential electric shock, the electric
> strength of mains-to-ground and mains-to-other circuits insulations must
> exceed the expected transient voltages.  (Electric strength requirements
> based on transient voltages are specified in IEC 60664-1, supported by
> research by Stimper.)
>
>
>
> The mains transients can be capacitively coupled to secondary circuits,
> depending on the configuration of the isolation scheme.  In most cases, the
> isolation scheme and the impedance of the secondary circuit attenuates the
> transient voltage to near zero. This point seems to be recognized by IEC
> 60101-1.
>
>
>
> Then, as Brian Kunde has said, secondary circuit devices such as relays,
> solenoids, and switching can generate transients in the secondary
> circuits.  In most cases, such transient voltages are small and are
> attenuated by the secondary source impedance.
>
>
>
> IEC 60601-1 has a similar requirement, although it includes clearance
> requirements for no-transient secondary circuits.  IEC 62368-1 does not
> have such a requirement.  I wonder what evidence or research supports
> transient voltages in secondary circuits?
>
>
>
> Best wishes for the holiday season,
>
> Rich
>
>
>
> *From:* Steve Brody 
> *Sent:* Thursday, December 1, 2022 12:51 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
>
> -
> 
>
> This message is from the IEEE Product Safety Engineering Society emc-pstc
> discussion list. To post a message to the list, send your e-mail to <
> emc-p...@ieee.org>
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> All emc-pstc postings are archived and searchable on the web at:
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>
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> David Heald 
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> 
>
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> emc-p...@ieee.org
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> All emc-pstc postings are archived and searchable on the web at:
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> David Heald dhe...@gmail.com
> 

Re: [PSES] Secondary creepage/clearance

[Richard Nute]

 

 

Hi Steve:

 

Mains circuits are subject to lightning and switching transients both 
line-to-neutral and line/neutral-to-ground.  The transients are normal; to 
prevent insulation breakdown and consequential electric shock, the electric 
strength of mains-to-ground and mains-to-other circuits insulations must exceed 
the expected transient voltages.  (Electric strength requirements based on 
transient voltages are specified in IEC 60664-1, supported by research by 
Stimper.) 

 

The mains transients can be capacitively coupled to secondary circuits, 
depending on the configuration of the isolation scheme.  In most cases, the 
isolation scheme and the impedance of the secondary circuit attenuates the 
transient voltage to near zero. This point seems to be recognized by IEC 
60101-1.

 

Then, as Brian Kunde has said, secondary circuit devices such as relays, 
solenoids, and switching can generate transients in the secondary circuits.  In 
most cases, such transient voltages are small and are attenuated by the 
secondary source impedance. 

 

IEC 60601-1 has a similar requirement, although it includes clearance 
requirements for no-transient secondary circuits.  IEC 62368-1 does not have 
such a requirement.  I wonder what evidence or research supports transient 
voltages in secondary circuits?  

 

Best wishes for the holiday season,

Rich

 

From: Steve Brody  
Sent: Thursday, December 1, 2022 12:51 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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[PSES] "how to fish" - UKCA extension legislation

[Lauren Crane]

For those keeping score at home on when the UKCA 2yr extension legislation is 
actually passed, this is how I am tracking

Goto https://commonsbusiness.parliament.uk/
Click on HTML or PDF version of "Daily Order Paper" in the "Today's business 
papers" section.

Search on "Metrology" and you should quickly (or eventually) land on 
information titled

"Secretary Grant Shapps

That the draft Product Safety and Metrology (Amendment and Transitional 
Provisions) Regulations 
2022,
 which were laid before this House on 14 November, be approved."

If you look today, you can see it is now "remaining order 36". It was 
"remaining order 41" on November 28.
Best Regards,
-Lauren


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Re: [PSES] Secondary creepage/clearance

[John Woodgate]

Sorry, a word missing:

, if your best efforts to find a documented rationale to not apply the 
requirement FAIL,


==
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 21:04, John Woodgate wrote:


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 

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

-


This message is from the IEEE Product Safety Engineering Society 
emc-pstc discussion list. To post a message to the list, send your 
e-mail to 


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unsubscribe) 

List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Mike Cantwell 

For policy questions, 

Re: [PSES] Secondary creepage/clearance

[John Woodgate]

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 

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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emc-pstc discussion list. To post a message to the list, send your 
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This message is from the IEEE Product Safety Engineering Society 

Re: [PSES] Secondary creepage/clearance

[Joe Randolph]

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

  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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Re: [PSES] Secondary creepage/clearance

[Brian Kunde]

The simple answer is that you need to provide creepage and clearance
distances in secondary circuits to avoid arcing when the circuit is
subjected to the absolute worst case surges and transients that the circuit
might see.  Since this can be difficult to determine, most people just use
the tables found in the standard. These tables are also found in the IP
Standards used by PCB CAD programs.

Notice that Table 6 says, "circuits derived from Mains", which means
circuits that are or can be affected by commonly known surges and
transients on the AC Mains.  These tables are created as a guide to take
some of the guess work and testing out of the equation.  Circuits that are
highly isolated or independently generated may not be subject to junk that
gets onto the AC Mains.  But keep in mind that there are some transients,
such as from relays, solenoids, switch contacts, etc. that can be quite
strong in a local circuit, so you must be careful not to underdesign.

I think the old version of the 61010-1 standard had an equation that took
into account the maximum transient overvoltage, but I think that has now
been integrated into Table 6 in Ed. 3 of the standard.

If you can run tests on your secondary circuits and can determine the worst
case surges and transients, you can design to those distances.  Also keep
in mind the use of PCB coatings, potting, pollution degree, etc..  Inner
layers of a PCB can have closer trace distances in most cases.

Good luck and have fun with it.

The Other Brian

On Thu, Dec 1, 2022 at 3:51 PM Steve Brody  wrote:

> 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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