Regan et al,
The basic electric shock info for the levels selected in the
product standards come from IEC 60479 series, Effects of electric shock on the
human body… There are two sets of curves in IEC 60479-1 based upon the data
collected and evaluated (from the literature). One set of curves is for AC and
the other is for DC. These plot three body effects; startle-reaction,
letgo-immobilization and Ventricular Fibrillation as a function of time. The
names for these effects primarily come from the effect of AC currents on the
body. The DC effects are not as well defined physiologically but are given the
same names for consistency. The product committees end up picking levels which
seem appropriate for the application and the values are not fully consistent
between product standards, in spite of the work of the IEC to make it so.
A major difficulty is that the body effects are from the current
while the product committees would like to specify voltage, which is easier to
measure and verify compliance.
The IEC long ago issued a simple 1201 Voltage Limits standard, aka 61201, which
was updated using a more complete evaluation and had a myriad of curves for the
various conditions based upon the choice of contact parameters selected. This
is so much more complicated than just selecting a fixed voltage for most
conditions and is not generally used in product standards.
So, in short, whether one picks 60Vdc or 70Vdc is not very
relevant in the overall human body effect picture; nor is a change of 4Vdc
around any of these values.
Finally, as Rich stated, the DC value is not related to the AC
value by the sqrt 2. This works well for moving from AC to equivalent DC
voltage for hi-pot testing purposes but provides no path to the human body
effect which is different, as has been discussed here.
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety & Regulatory Affairs Consultant
PO Box 1067
Albany, ORe 97321-0413
503/452-1201
IEEE Life Fellow
IEEE PSES 2020 Distinguished Lecturer
<mailto:[email protected]> [email protected]
From: Regan Arndt <[email protected]>
Sent: Tuesday, February 25, 2020 8:49 PM
To: [email protected]
Subject: Re: [PSES] IEC 61010-1:2010 hazardous DC voltage
Hi Rich.
Thanks for your feedback.
Correction/clarification. I was not trying to ‘convert’ to DC using 1.414 (root
2).
I merely used that ‘multiplication factor’ (1.414 & sometimes just 1.4) based
on the widely used/misused?/abused? that is used in the industry when
determining ‘equivalent’ DC values, just like one commonly does when
calculating the hipot test values.
See:
https://electrical-engineering-portal.com/what-is-hipot-testing-dielectric-strength-test
<https://urldefense.proofpoint.com/v2/url?u=https-3A__electrical-2Dengineering-2Dportal.com_what-2Dis-2Dhipot-2Dtesting-2Ddielectric-2Dstrength-2Dtest&d=DwMFaQ&c=q6k2DsTcEGCcCb_WtVSz6hhIl8hvYssy7sH8ZwfbbKU&r=9-kTQUJB47k5_bHz_YekCwOWfoQDGgqgofVdnvpCXhM&m=X4OfXcJKn2LCMhQAhagkIEb6yDHp7Th9Mn0aSM9F6M4&s=57RvY_cM21TMTgAGuiIGMnZD0a7EcjWCvdfn0geu-kw&e=>
, where Jignesh Parmar quotes in his article: “Therefore, if we use dc test
voltage, we ensure that the dc test voltage is under root 2 (or 1.414) times
the ac test voltage, so the value of the dc voltage is equal to the ac voltage
peaks.”
Another classic example comes from the 60950 standard for hipot values. 1500
VAC/2121 DC (calculation factor = 1.414)
That being said, I look forward to hear a response from someone on TC66 on why
they chose 70V.
It would also be great if you could do a whitepaper (& speak) on the
understanding of how the body reacts to AC & DC for this year’s PSES symposium
in Chicago? 😉
Regan
On Tue, Feb 25, 2020 at 4:07 PM Richard Nute <[email protected]
<mailto:[email protected]> > wrote:
Hi Regan:
The “bump” occurred from 1st edition, 1990, to 2nd edition, 2001. The 2nd,
2001, and 3rd, 2010, are the same.
Be careful with your math and DC interpretation. The rms voltage limit is 33.
The ac peak is 1.414 x 33 = 46.7. The DC is 70, which is unrelated to the AC
voltages (which is because of how the body reacts to AC and DC).
As to the rationale for the change from 1st to 2nd, I suggest you find a member
of TC66 and ask for the documents preceding the 2nd.
Touch voltages are specified in IEC TS 61201. In this standard both 30 and 33
volts rms are listed, with very little difference in body reaction. Same for
60 versus 70 volts DC.
Best regards,
Rich
From: Regan Arndt <[email protected] <mailto:[email protected]> >
Sent: Tuesday, February 25, 2020 2:38 PM
To: [email protected] <mailto:[email protected]>
Subject: [PSES] IEC 61010-1:2010 hazardous DC voltage
Dear fellow members,
I am trying to understand the 'rationale/history' of why TC66 bumped up the DC
voltage by a mere 4 volts for hazardous voltages.
As we know by simple math, 46.7 Vp x 1.414 = 66 VDC.............where, why and
how did the extra 4 volts come about?
I need a history lesson here.... ;)
Also, will these voltages also come back to normal in Ed 4? (i.e. 42.4 Vp, 60
VDC)
Thanks for shedding any light on this?
Regan Arndt
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