Re: [PSES] EN 62368-1 query

[Mick Maytum]

On 26-Oct-15 6:29 PM, Scott Aldous wrote:

_Table 5 (Capacitor Energy)_

For the energy from a capacitor, the table takes into account 
capacitance and voltage, so both need to be taken into account since 
the equation for available energy from a capacitor includes both 
variables. This is similar to 2.1.1.5c)2) from 60950-1.


IEC 60479-2 provides a linearised treatment of a capacitive discharge to 
the body. The examples consider both capacitive discharge charge and 
energy. In TC108 safety documents IEC 60950-21 and the coming IEC 
62368-3 you will find voltage versus maximum capacitance figures. What 
is counter-intuitive is that these curves are set by the capacitor charge.
If you calculate the capacitor value from the maximum body energy value 
far greater values of capacitance result. Whoever calculated the figure 
capacitance values back in 2000 or so worked out that for Remote Feeding 
Telecommunication circuits the capacitive charge was the critical 
parameter, not energy, setting the maximum capacitance value.

Regards
Mick

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Re: [PSES] EN 62368-1 query

[Richard Nute]

 

 

Hi Ron:

 

 

>But, a capacitor charged to such an open-circuit
voltage need to also be rated for that voltage
(probably a DUH moment). Correct?

 

Yes.

 

>Is Table 2 of IEC 61201:1992 equivalent to Table
A.2 of IEC 61201:2007?

 

Yes.

 

>ECMA 287 Table 3.4 ES1 values decrease from 60 V
instead of increasing from 60 V from IEC 62368-1
Table 5 ES1 values.

 

In ECMA 287, Table 3.4 is ordered by capacitance,
while IEC 61201 is ordered by voltage.  The ES1
voltage values in ECMA 287 "are derived from Table
2 of IEC 61201" and are not the values in IEC
61201.   IEC 62368-1 uses the table verbatim.

 

>So, the purpose of 5.2.2.3 is intended to apply
to those capacitors in which their charged
voltages are exposed in ES1 circuits during normal
operating conditions and become exposed in ES2
circuits only after a fault?

 

Yes, although I would use the word "accessible"
as, in the IEC, the word "exposed" has a different
meaning.  

 

(ES1 is not necessarily a circuit, but a voltage
with respect to ground from 0 to 42.4 or a current
to ground from 0 to 0.5 mA.)

Need any more clarification?

 

 

Best regards,

Rich

 

 

 


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Re: [PSES] EN 62368-1 query

[Richard Nute]

 

Hi Ron:

 

 

The values in Table 5 are taken, directly, from
IEC 61201, Table A.2 and Figure A.1 (notes 1 and
2).  See Annex A, IEC 61201, for further
information about these values.

 

Upeak is not the correct term; the voltage is the
open-circuit voltage to which the capacitor is
charged.  The correct term would be "prospective
touch voltage" as specified in the note to
5.2.2.1.   

 

For 300 nF and greater, the voltage values are the
d.c. values in Table 4.  As the capacitance gets
smaller, the voltage is larger, but the effect on
the body is, supposedly, the same.  See Clause 11,
IEC 60479.  (We have very little modern
experimental evidence of this theory.)  I
personally doubt that some of the
voltage/capacitance combinations would be benign,
but I'm not going to be the guinea pig that
verifies the table!  Perhaps some of the papers
listed in the IEC 60479 bibliography show that the
values are valid.

 

Recall that ES1 can be accessible.  ES2 is only
accessible in the event of a fault.  ES3 is never
accessible.

 

Back in the old days, plotters used electrostatic
paper hold-down; the platen was charged to a high
voltage, so the capacitance was critical to avoid
an unpleasant electric shock.  The voltage source
used to charge the capacitor would have to be very
wimpy as it, too, would have to be ES1.  I don't
know of a similar construction or equipment today
that employs an accessible stored charge.

 

I hope this provides some answers for you.  If
not, just ask!

 

 

Best regards,

Rich

 

 

 


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Re: [PSES] EN 62368-1 query

[Ronald Pickard]

Hi Rich,
Thanks for your reply. And, neither would I be in line to be a guinea pig for 
that, but that does remind me of the opening scene in Ghostbusters. :)

But, a capacitor charged to such an open-circuit voltage need to also be rated 
for that voltage (probably a DUH moment). Correct?

I don't as yet have a copy of IEC 61201:2007, but I know that ECMA 287 
(3.2.1.2) Table 3.4 refers to Table 2 of IEC 61201:1992, but the ECMA 287 Table 
3.4 ES1 values decrease from 60 V instead of increasing from 60 V from IEC 
62368-1 Table 5 ES1 values. Is Table 2 of IEC 61201:1992 equivalent to Table 
A.2 of IEC 61201:2007?

So, the purpose of 5.2.2.3 is intended to apply to those capacitors in which 
their charged voltages are exposed in ES1 circuits during normal operating 
conditions and become exposed in ES2 circuits only after a fault? If this is 
correct, then I wish that the authors made it clearer.

Also, a commercially available product with accessible stored charge that comes 
to mind is the Van de Graaff generator and although not technically utilizing a 
stored charge, there is a Jacob's Ladder. Both are primarily intended for 
experimentation and fun.

I look forward to your reply.

Best Regards

Ron Pickard
Regulatory Compliance Engineer
Compound Photonics
D | +1 (602) 883-8039

From: Richard Nute [mailto:ri...@ieee.org]
Sent: Monday, October 26, 2015 12:42 PM
To: Ronald Pickard <ronald.pick...@compoundphotonics.com>; 
EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] EN 62368-1 query


Hi Ron:


The values in Table 5 are taken, directly, from IEC 61201, Table A.2 and Figure 
A.1 (notes 1 and 2).  See Annex A, IEC 61201, for further information about 
these values.

Upeak is not the correct term; the voltage is the open-circuit voltage to which 
the capacitor is charged.  The correct term would be "prospective touch 
voltage" as specified in the note to 5.2.2.1.

For 300 nF and greater, the voltage values are the d.c. values in Table 4.  As 
the capacitance gets smaller, the voltage is larger, but the effect on the body 
is, supposedly, the same.  See Clause 11, IEC 60479.  (We have very little 
modern experimental evidence of this theory.)  I personally doubt that some of 
the voltage/capacitance combinations would be benign, but I'm not going to be 
the guinea pig that verifies the table!  Perhaps some of the papers listed in 
the IEC 60479 bibliography show that the values are valid.

Recall that ES1 can be accessible.  ES2 is only accessible in the event of a 
fault.  ES3 is never accessible.

Back in the old days, plotters used electrostatic paper hold-down; the platen 
was charged to a high voltage, so the capacitance was critical to avoid an 
unpleasant electric shock.  The voltage source used to charge the capacitor 
would have to be very wimpy as it, too, would have to be ES1.  I don't know of 
a similar construction or equipment today that employs an accessible stored 
charge.

I hope this provides some answers for you.  If not, just ask!


Best regards,
Rich




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Re: [PSES] EN 62368-1 query

[Ronald Pickard]

Hi Rich,
Thank you for your patience. Acknowledged on my choice of wording.

No more clarification need on this. Thank you.

Best regards,

Ron Pickard
Regulatory Compliance Engineer
Compound Photonics
D | +1 (602) 883-8039

From: Richard Nute [mailto:ri...@ieee.org]
Sent: Monday, October 26, 2015 3:58 PM
To: Ronald Pickard <ronald.pick...@compoundphotonics.com>; 
EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] EN 62368-1 query



Hi Ron:


>But, a capacitor charged to such an open-circuit voltage need to also be rated 
>for that voltage (probably a DUH moment). Correct?

Yes.

>Is Table 2 of IEC 61201:1992 equivalent to Table A.2 of IEC 61201:2007?

Yes.

>ECMA 287 Table 3.4 ES1 values decrease from 60 V instead of increasing from 60 
>V from IEC 62368-1 Table 5 ES1 values.

In ECMA 287, Table 3.4 is ordered by capacitance, while IEC 61201 is ordered by 
voltage.  The ES1 voltage values in ECMA 287 "are derived from Table 2 of IEC 
61201" and are not the values in IEC 61201.   IEC 62368-1 uses the table 
verbatim.

>So, the purpose of 5.2.2.3 is intended to apply to those capacitors in which 
>their charged voltages are exposed in ES1 circuits during normal operating 
>conditions and become exposed in ES2 circuits only after a fault?

Yes, although I would use the word "accessible" as, in the IEC, the word 
"exposed" has a different meaning.

(ES1 is not necessarily a circuit, but a voltage with respect to ground from 0 
to 42.4 or a current to ground from 0 to 0.5 mA.)

Need any more clarification?


Best regards,
Rich




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Re: [PSES] EN 62368-1 query

[Scott Aldous]

Hi Ronald,

It may be helpful for you to purchase a copy of 62368-2, which has the
rationale for the requirements in 62368-1.

Others can provide more detail and probably explain better than I, but in
general Table 4 has voltage *or* current limits, and Table 5 has
capacitance *and* voltage limits. Table 4 is based on current (concerned
with electrical shock), while Table 5 is based on energy (concerned with
energy hazard), so you aren't comparing apples to apples by just looking at
the voltage values in each table.

*Table 4 (Electric Shock)*

See Figure 21, and the explanation at the end of 5.2.2.1. "For any voltage
up to the voltage limit, there is no limit for the current. Likewise for
any current up to the current limit, there is no limit for the voltage..."

   - For low voltage circuits, the current is limited by the impedance
   through the human body. The currents assumed to flow through the human body
   at the ES1 voltage limits are lower than that which causes undesirable
   physiological effects.
   - There could be an ES1 circuit up to 25kV, or even higher in theory
   (with currents in normal, abnormal and single fault conditions limited to
   comply with the applicable limit). As long as the current is limited to
   values below that which causes undesirable physiological effects, the
   voltage doesn't matter. This is similar to the Limited Current Circuit from
   60950-1, clause 2.4.

*Table 5 (Capacitor Energy)*

For the energy from a capacitor, the table takes into account capacitance
and voltage, so both need to be taken into account since the equation for
available energy from a capacitor includes both variables. This is similar
to 2.1.1.5c)2) from 60950-1.

A bit more info here

(see
section III).



On Mon, Oct 26, 2015 at 10:31 AM, Ronald Pickard <
ronald.pick...@compoundphotonics.com> wrote:

> For all those more familiar than I with this standard, I would appreciate
> a clarification.
>
>
>
> I’ve just purchased EN 62368-1 (assuming IEC 62368-1, too) and have
> started immersing myself in it, but in 5.2.2.3 (Table 5) ES1/ES2 voltage
> limits from a charged capacitor appear to violate the ES1/ES2 voltage
> limits from 5.2.2.2 (Table 4). As Table 5 doesn’t address Vdc or Vac, I am
> assuming absolute voltages (Upeak not defined) apply here. It appears that
> up to 25KV (50KV for ES2) are allowed depending on capacitor value. And,
> how would a capacitor be charged to 25KV in or then connected to an ES1
> circuit without consequence? Am I reading this correctly? Are these voltage
> limits intended for capacitor rating limits only? What is the purpose of
> 5.2.2.3 and Table 5?
>
>
>
> The further I get with this, the more questions that pop up for me. I
> can’t seem to resolve this in my own feeble grey matter as to why such
> voltages would be allowed. I would like to understand this better and would
> appreciate if someone would clarify this for me and possibly others that
> may have these or similar questions as well.
>
>
>
> I look forward to your reply.
>
>
>
> Best regards,
>
>
>
> *Ronald Pickard*
> Regulatory Compliance Engineer
> *Compound Photonics*
> D | +1 (602) 883-8039
>
> -
> 
>
> 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
>
> All emc-pstc postings are archived and searchable on the web at:
> http://www.ieee-pses.org/emc-pstc.html
>
> Attachments are not permitted but the IEEE PSES Online Communities site at
> http://product-compliance.oc.ieee.org/ can be used for graphics (in
> well-used formats), large files, etc.
>
> Website: http://www.ieee-pses.org/
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>



-- 
Scott Aldous
Compliance Engineer
Google
650-253-1994
scottald...@google.com

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