Vincent et al,
There have been several really good responses to your question
on this listserv; it’s great to see everyone chime in and provide their info.
I’d like to add a bit of background and detail to all of this.
Scott pointed out the time vs current curve in the ABB paper.
This curve is from the original version of IEC 60479-1 ‘Effects of electric
current on humans …’ and has been slightly updated in the current version of
the standard. The small changes do not however affect the overall argument nor
the application of this base data to the problem at hand.
There are 3 electric shock levels stated in 60479-1. Perception
of electric current is highly variable among persons and extends well into the
low microamp range. In 60479-1, the lowest level, the startle-reaction level
(‘a’ line) is at 0.5mArms level; the next level, the letgo-immobilization level
(‘b’ line) is 5mArms for times above one ac cycle (which provides protection
for all individuals – men, women and children); the third level, the
Ventricular Fibrillation level (‘c1, c2 and c3’ lines) is intended to
illustrate a statistical distribution for VF and the lowest, ‘c1’ line is
30mArms for times above one ac cycle.
The selection of 5mArms for the GFCI units is chosen to prevent
immobilization if the earth/ground current goes above that value. These units
are widely used in North America especially in homes but also in commercial
buildings anywhere there is ground present – bathrooms, kitchens, laundries,
garage and outdoor outlets.
The RCD units have been used in Europe for some time for
industrial use intended to prevent serious hazard to workers. The choice of
the 30mArms limit has been considered adequate for that application.
There is some question about the adequacy of the 30mArms limit
in that the ‘c1’ line is not an absolute limit for persons. It is a
statistical limit, having been considered a 5% line in the past (but some folks
today like to call it a 1% line). In either case it is clear that there are
humans who lie to the left of this line and will be subject to VF at lower
currents. [When considered a 5% line it means that there are about 350 Million
persons on planet earth to the left of the curve.]
The US will introduce a higher current device for use in
industrial and other high power uses (such as electric car chargers). It looks
like the devices will be 15mArms or 25mArms (and the limit prescribed for
various installations).
A further issue is that mains electronic switching devices are
no longer sinusoidal and the circuits on which they work are subject to
impulses which will push the current levels in the circuit being protected
above the desired level (whether 5mArms, 15mArms, 25mArms or 30mArms). The
impulses are invading the space of the next higher protection level since it is
the peak value of the impulse which causes the harm. These impulse currents
can be harmful to humans when accessible.
Today there are issues using electronic switching units
connected to GFCI and RCD units. The feedback signals from the equipment will,
in some cases, either falsely trip the protection device or not properly trip
when the current exceeds the protection value.
Obviously coordinated levels for outgoing emissions and incoming
susceptibility between equipments need to be fully worked out.
Hopefully this further explanation is helpful to you and other
on this network.
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety & Regulatory Affairs Consultant
PO Box 23427
Tigard, ORe 97281-3427
503/452-1201
<mailto:p.perk...@ieee.org> p.perk...@ieee.org
From: Scott Aldous [mailto:00000220f70c299a-dmarc-requ...@ieee.org]
Sent: Thursday, February 16, 2017 8:29 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Questions on RCB, RCCB and ELCBs
Hi Vincent,
Here
<https://library.e.abb.com/public/c4e584f06cc6c4fbc1257ad800496193/2CSC420004B0201_RCDs%20EN.pdf>
is a technical guide from ABB that you may find helpful. With regard to the
30mA trip level for an RCD, the paper refers to IEC 60479-1 and reproduces a
Figure from that standard on page 2 relating effects on the body from exposure
to ac currents (15 Hz to 100 Hz) with different durations. I don't believe the
paper explains this, but this graph is specific to a left hand to feet current
path through the body. The version of the standard that I have actually has a
figure that is slightly different from the ABB paper, FYI.
The paper seems to indicate that the 30mA level was chosen since it marks the
delineation between regions made by the c1 curve. Referring to the table on the
next page (the table from the standard has more information), although below
that current level let-go can occur it does not mention danger of ventricular
fibrillation. If the assumption regarding the reason for this choice is
correct, it appears that the IEC chose ventricular fibrillation as the major
consideration, likely also considering that 30mA is still within zone 2 (AC-2
in the standard) for durations up to about 200ms and that people will generally
react to move away from contact. As John mentions, likelihood of nuisance
tripping was also surely taken into account when choosing this level. It
appears that the UL standard focused on prevention of effects at a less severe
level. Note that 5mA is always within zone 2 (AC-2) regardless of duration.
That being said, I am not familiar with the history of the development of the
relevant standards. If there are folks on this forum who are, I would love to
see a more accurate or more detailed explanation.
On Thu, Feb 16, 2017 at 12:49 AM, John Woodgate <jmw1...@btinternet.com
<mailto:jmw1...@btinternet.com> > wrote:
1. That's a really big question and the really big answer is too big for a
mailing list. Search on the web for descriptions and/or comparisons.
2. The IEC standard is an international agreement. I suppose the GFCI is a
US-only (or NA-only) specification. Fault currents are obviously half with 120
V supplies versus 230 V supplies. At 230 V, 5 mA would cause nuisance tripping
and problems with protective conductor currents due to capacitance from L to
PEC.
3. ELCBs required a PEC connection, so if the PEC is broken, the protection
does not work. RCCBs detect the difference between L and N currents and do not
use a PEC connection.
With best wishes DESIGN IT IN! OOO – Own Opinions Only
<http://www.jmwa.demon.co.uk/> www.jmwa.demon.co.uk J M Woodgate and
Associates Rayleigh England
Sylvae in aeternum manent.
From: Vincent Lee [mailto:000008e6c8d35910-dmarc-requ...@ieee.org
<mailto:000008e6c8d35910-dmarc-requ...@ieee.org> ]
Sent: Thursday, February 16, 2017 3:04 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG>
Subject: [PSES] Questions on RCB, RCCB and ELCBs
Hi all,
I am Vincent, newbies in Product Safety. Hence, I sincerely hope to seek your
professional answers to my following questions,
1) What are the major differences between RCB, RCCB, GFCI and GFEP ?
2) If the human-let-go-current-threshold is about 10mA, why does IEC 61008
RCCBs used in Household being specified at 30mA trip current while GFCI used in
Household are specified at 5mA (+/- 1mA) ?
3) I heard that Residual Current Circuit Breaker are replacing Electrical
Leakage Circuit Breaker, in what ways are RCCB better than ELCB for electrical
safety protection that causes ELCB being replaced?
Regards,
Vincent
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