Mick, Thanx for the reply given on this thread.
I am familiar with the 60479 clauses you describe. My overall
comment is that 60479 folks primary focus is on preventing VF (not killing
people). Much of what you quoted relates to such electric shock situations.
Because of the data spread there probably are a few folks who lie below the
curves shown in the standard. Tasers meet these requirements yet there are
occasional deaths with their use; the ‘almost perfect weapon’ in my opinion.
In the product standards the allowed electric shock level is
always set much lower so that the VF region is not involved. The upper limit
to electric shock from equipment is the Letgo-immobilization limit of
5mArms/7mApk under fault conditions. The long time separation to allow the
heart to reset doesn’t come into play for this effect so it is irrelevant. The
peak current is the major factor that needs to be controlled.
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety & Regulatory Affairs Consultant
PO Box 23427
Tigard, ORe 97281-3427
503/452-1201
IEEE Life Fellow
<mailto:[email protected]> [email protected]
Entropy ain’t what it used to be
From: Mick Maytum <[email protected]>
Sent: Tuesday, March 12, 2019 1:03 PM
To: [email protected]
Subject: Re: [PSES] classification of the output
Joe Randolph and I talked about “pulsed power” delivery at the 2019 ATIS-PEG
conference last week and how it should be treated.
A good starting point is the IEC 60479 series of documents on “Effects of
current on human beings and livestock”. IEC 62368-1 mentions the time locked
IEC TS 60479-1:2005, but the current version is IEC 60479-1:2018. The IEC TS
60479-2:2017 variant is particularly interesting as clause 9 covers “Effects of
current pulse bursts and random complex irregular waveforms”. For sequential
pulses separated by > 300 ms there isn’t a cumulative effect on the heart and
each pulse can be treated as single, non-repetitive pulse of current. For
safety, I believe pulsed power systems will insert this separation time when
any non-load currents are detected to delay any following power pulse.
Thus only the effects of a single power pulse need to be evaluated provided the
safety separation is >0.3 s. Primarily IEC TS 60479-2:2017 is seeking to
establish a “no fibrillation” condition, which is higher stress level than
you’d want for a safety standard.
A 2018 ATIS-PEG conference paper on IEC TS 60479-2:2017 gave an example
evaluation using the quoted pulsed currents produced by a TASER® gun. Safety
tip - if anyone is pointing a TASER® gun at you, yell out you have a
pre-existing medical condition.
Regards,
Mick
Safety and Telecom
Standards
<mailto:[email protected]> [email protected]
https://ict-surge-protection-essays.co.uk/
------ Original Message ------
From: "Joe Randolph" <[email protected]
<mailto:[email protected]> >
To: [email protected] <mailto:[email protected]>
Sent: 12/03/2019 17:54:36
Subject: Re: [PSES] classification of the output
Hi Pete:
This discussion reminds me of some things I have been hearing about “digital
power” as a way to deliver large amounts of power while keeping the circuit
classification to ES1 or ES2. A company called Voltserver has been promoting
(and deploying) this technology.
I know few details about the scheme, and I’m not familiar with how IEC 62368-1
evaluates things such as touch current.
However, as I understand it, the “digital power” method uses a series of short
pulses with off periods during which the power sourcing device attempts to
detect a fault condition. The power is immediately cut off if a fault
condition is detected. I have heard that the pulse frequency is in the range
of 7 KHz, and the voltages can be up to 380 V. The key to making this scheme
even plausible is that the system must respond VERY quickly to a fault
condition (such as a human touching a live conductor).
I’m interested in hearing your thoughts (and hopefully Rich Nute’s thoughts
too) regarding how the touch current tests in IEC 62368-1 might apply to such a
system. I don’t know whether such a system would pass or fail the IEC 62368-1
tests.
Regardless of whether such a system would pass or fail the existing tests in
IEC-62368-1, I think the important thing is to go back to first principles and
evaluate whether the proposed “digital power” can be made sufficiently safe to
prevent harm to humans.
Thanks,
Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
<mailto:[email protected]> [email protected]
<http://www.randolph-telecom.com> http://www.randolph-telecom.com
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