Hi Jim, My comments below are focused on the USA.
Will the machine be NRTL Listed as a whole? If not, then branch circuit rated devices will be required in the end installation. If so, then it will be the judgment of the NRTL that does the Listing evaluation. I would expect that they may require that a short circuit current rating be assigned to the machine. The question of whether branch or supplementary overcurrent protection is required internally may depend on the overall short circuit current rating and whether the internal overcurrent devices (and downstream components) can withstand the worst case short circuit currents without giving rise to a hazardous situation. You may want to look at UL 508A, Supplement SB. In that supplement, there is a method to assign a short circuit current rating without test. It assumes a branch circuit rated breaker can withstand 5kA whereas a supplementary protector can only withstand 0.2kA. Of course, testing can be performed instead, or your devices could have different ratings based on their own certifications. Providing an upstream fault current limiting device can be beneficial also. Some additional info from UL here <http://ul.com/wp-content/uploads/2014/04/ul_OvercurrentProtectionSupplementary.pdf> . Of course, abnormal tests will also be performed as part of the overall Listing of the machine, with the internal protection and external overcurrent protection in circuit. Results that are dependent on testing may lead you to have to call out a specific external overcurrent protection device in the manual (i.e. the one it was tested with). There may be other considerations specific to the standard(s) applied for Listing. On Tue, Apr 28, 2015 at 7:40 AM, Jim Hulbert <[email protected]> wrote: > I have been looking at overload protection requirements for machinery, > and I am a little unsure about application of branch protection versus > supplementary protection. For example, suppose a machine is powered from > AC mains (single phase or 3-phase, I don’t think it matters). The power > entry to the machine contains a main disconnect (breaker). The AC power is > then distributed within the machine to power supplies, motor controllers, > and internal-only outlets. These internal outlets are used during > installation by trained service personnel for defined auxiliary devices and > are accessible behind tool-accessed covers, not intended for operator > access. Each internally distributed circuit is further protected by a > overcurrent device (breaker) in addition to the main disconnect breaker. > Individual motors have further overcurrent protection. The machine > installation requires the customer to provide a dedicated circuit of > sufficient capacity for the machine, with a nearby disconnect. > > > > Questions: If the facility disconnect is a UL 489 listed circuit breaker > that meets the requirements for branch protection, are we required to have > additional branch protection within our machine or is supplementary > protection sufficient? If we do need branch protection in the machine > itself, is it sufficient only for the main disconnect at the power input? > Are there differences in the requirements for U.S. and Europe? > > > > Thanks. > > > > *Jim Hulbert* > > > > ------------------------------ > > - > ---------------------------------------------------------------- > > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. 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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]>
