FYI - Regarding the SCCR, it's really not about the interrupt rating of overcurrent protection devices. It relates to the ability of the equipment to withstand the fault currents that overcurrent devices would let through in a short circuit event. Looking through the supplement in UL 508A is instructive. If you try to evaluate through the "weakest link" method rather than testing, values are assigned to components commonly found in switchgear, including bus bars. If you have overcurrent protection that is current lmiting, it helps reduce the required withstand rating of components downstream, but this is dependent on the extent of current limiting rather than interrupt rating.
On Tue, Nov 25, 2014 at 8:33 AM, Ted Eckert <[email protected]> wrote: > Hello Brian, > > The role the enclosure plays in arc flash protection may be less than you > would expect. The concern about arc flash isn't for normal operation of the > equipment. Arc flash and arc blasts are considered an issue for the > servicing of equipment. The concern is that service personnel may > accidentally create a short circuit between two phases or a phase and > ground. This could occur due to improperly de-energizing circuits or when a > metal tool or part is accidentally placed such that it creates a short > circuit. > > NFPA 70E requires that the arc flash boundary be calculated, although it > is assumed to be 4 feet (1.2 meters) for typical small equipment rated 250 > V or less connected to a branch circuit breaker. The boundary will be > greater depending on the rating of the circuits overcurrent protector. NFPA > 70E requires that untrained and unprotected personnel must remain outside > of that boundary during the service of equipment. Personnel inside of that > boundary must be properly trained and they must be wearing the correct PPE > based on the arc flash hazard risk. Since this is an issue during the > servicing of equipment when doors are open and covers are off, the > enclosure provides no protection. The arc flash rules just require marking > indicating the hazard so that service personnel can take the proper > precautions. > > Field wired equipment that never needs to be serviced live should be > marked with instructions to disconnect all power before servicing. If this > can be done properly, arc flash marking may not be required. The marking > may not be required if the equipment is installed with an external > disconnect. Arc flash marking is generally not required for plug connected > equipment. > > Pick your favorite search engine and search for "arc flash labels" and you > will find examples of the marking typically required. > > Ted Eckert > Compliance Engineer > Microsoft Corporation > [email protected] > > The opinions expressed are my own and do not necessarily reflect those of > my employer. > > -----Original Message----- > From: Kunde, Brian [mailto:[email protected]] > Sent: Tuesday, November 25, 2014 6:08 AM > To: [email protected] > Subject: Re: [PSES] Arc Flash Requirements NFPA 79 > > Thanks for the input. > > Because our products are Laboratory Equipment and not Industrial Machines, > I assume NFPA 79 would not apply. So the SCCR on the nameplate would not be > required. It would be difficult to provide anyway. Since we are only > required to provide supplementary over current protection the SCCR value is > really unknown. Our Circuit Breaker manufacturer rates their parts with a > 5kA SCCR but to my understanding they don't even have to survive the test. > So the Branch Circuit Breaker is relied upon to provide the protection and > the necessary SCCR value would be based on the Customer's power system. > > The SCCR value is interesting to me. For those of you who has to design > your products to meet a specific SCCR value, what do you design for? Are > there typical values you shoot for? How high of value must you design for? > So if you design for say 10kA and your customer wants 50kA what do you do? > > Thanks for the information regarding Arc Flash. I'm assuming that if our > chassis (fire enclosure) meets the constructional requirements of IEC/EN/UL > 61010-1 that it should contain an Arc Flash; especially with a 230VAC > powered instrument where the energy to produce an Arc Flash is somewhat > limited. I have also been asked by customers if our chassis meet the NEMA > requirements. I assume the question is in regards to Arc Flash. > > Thanks again for the info. It was most helpful. > > The Other Brian > > > -----Original Message----- > From: Mr. Doug Nix C.E.T. [mailto:[email protected]] > Sent: Monday, November 24, 2014 4:32 PM > To: [email protected] > Subject: Re: [PSES] Arc Flash Requirements NFPA 79 > > Dave, Brian, > > Electrical field inspectors commonly require that labels of the type I > referenced be installed by the manufacturer. The detailed labels with the > arc flash degree and the details on the PPE requirements can only be > installed post installation and post arc-flash hazard analysis. This is a > workplace requirement, and not a manufacturer requirement. > > Dave is correct about the Short-Circuit Withstand Rating (SCCR). This has > been part of the nameplate requirements for many years. > > Doug > > On 24-Nov-14, at 16:10, Nyffenegger, Dave <[email protected]> > wrote: > > > Over the years recently there has been more emphasis on arc flash due to > injuries. You can search on it. The issue is the potential for arc flash > when the control panels are open and powered by the electrician which can > cause clothing to catch fire. It's not so much an issue of containing an > arc flash within the enclosure, a fire enclosure should do this regardless. > > > > I asked our NRTL test engineer about arc flash warning label > requirements a few months ago and he pointed out that wording in NFPA 70 > states that arc flash warning labels are to be applied on site during > machine installation. There is not a requirement for the manufacturer to > apply the warning. I don't have my copy of NFPA 70 in front of me but I > recall I confirmed the wording. I recall I also confirmed the same on the > OSHA web site. These labels can be purchased off the shelf. > > > > NFPA-79: Sec. 16.4 requires the SCCR of electrical control panels to be > put on the product nameplate. UL 508A: Supplement SB has instructions for > determining SCCR. If your product doesn't contain an electrical control > panel and no internal branch circuits you may not need the rating. > > > > I've only had an NRTL certify to NFPA 79 for field labeling/marking. > > > > -Dave > > > > -----Original Message----- > > From: Kunde, Brian [mailto:[email protected]] > > Sent: Monday, November 24, 2014 3:29 PM > > To: [email protected] > > Subject: [PSES] Arc Flash Requirements NFPA 79 > > > > Our company produces Laboratory Equipment. We design to the IEC/EN/UL > 61010-1 series of standards and the NFPA 70 NEC. > > > > Some of our instruments can be quite large; slightly bigger than an > upright piano. They typically are powered by 230VAC, 20A to 50A branch > circuits. It is typical that our instruments are installed near or in a > heavy industrial environment even though they are not considered Industrial > Machines. They are sometimes mistaken as Industrial Machines. > > > > Recently, we have had customers ask the following questions about our > instruments: > > > > * Proof that the electrical system complies to NFPA 79. > > * Are the electrical enclosures marked for arc flash hazard per > NFPA 79? > > * What is the Short Circuit Current Rating (SCCR) of our > instruments? > > > > > > Typically we simply reply that our instruments are not Industrial > Machines and that is that. However, if there is information we can provide > that would be helpful, we would like to do so. > > > > I can see where our customer may wish to power our instrument from a > circuit that is capable of producing very high short circuit current (SCC). > If this exceeds the 5kA rating of our internal Supplementary Protection > Device, then our customer would have to supply a Brach Circuit Breaker that > can handle the SCC. > > > > High SCC can also cause a concern for Arc Flash. I do not know the > requirements of NFPA 79 and how it affects Arc Flash. For instance, since > our chassis meets the mechanical requirements called out in IEC 61010-1, is > it likely that our chasses will contain the arc flash hazards? > > > > Is there any part of NFPA 79 that could apply to our instruments; to the > mechanical or electrical system? > > > > Has something changed recently which would explain why we are now > receiving these type of questions? > > > > Thanks for any input or advice. > > > > The Other Brian > > > > > > > > > > ________________________________ > > > > LECO Corporation Notice: This communication may contain confidential > information intended for the named recipient(s) only. If you received this > by mistake, please destroy it and notify us of the error. Thank you. > > > > - > > ---------------------------------------------------------------- > > 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 <[email protected]> > > > > 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/ > > Instructions: http://www.ieee-pses.org/list.html (including how to > > unsubscribe) List rules: http://www.ieee-pses.org/listrules.html > > > > For help, send mail to the list administrators: > > Scott Douglas <[email protected]> > > Mike Cantwell <[email protected]> > > > > For policy questions, send mail to: > > Jim Bacher: <[email protected]> > > David Heald: <[email protected]> > > > > - > > ---------------------------------------------------------------- > > 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 <[email protected]> > > > > 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/ > > Instructions: http://www.ieee-pses.org/list.html (including how to > > unsubscribe) List rules: http://www.ieee-pses.org/listrules.html > > > > For help, send mail to the list administrators: > > Scott Douglas <[email protected]> > > Mike Cantwell <[email protected]> > > > > For policy questions, send mail to: > > Jim Bacher: <[email protected]> > > David Heald: <[email protected]> > > - > ---------------------------------------------------------------- > 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 < > [email protected]> > > 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/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <[email protected]> > Mike Cantwell <[email protected]> > > For policy questions, send mail to: > Jim Bacher: <[email protected]> > David Heald: <[email protected]> > ________________________________ > > LECO Corporation Notice: This communication may contain confidential > information intended for the named recipient(s) only. If you received this > by mistake, please destroy it and notify us of the error. Thank you. > > - > ---------------------------------------------------------------- > 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 < > [email protected]> > > 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/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <[email protected]> > Mike Cantwell <[email protected]> > > For policy questions, send mail to: > Jim Bacher: <[email protected]> > David Heald: <[email protected]> > > - > ---------------------------------------------------------------- > 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 < > [email protected]> > > 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/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <[email protected]> > Mike Cantwell <[email protected]> > > For policy questions, send mail to: > Jim Bacher: <[email protected]> > David Heald: <[email protected]> > -- Scott Aldous Compliance Engineer Google 650-253-1994 [email protected] - ---------------------------------------------------------------- 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 <[email protected]> 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/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
