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 - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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