Mr. O’Connell gives me too much credit. It’s been 10 years since I did much work in this area<http://www.apc.com/salestools/KSIH-6Y6UU5/KSIH-6Y6UU5_R0_EN.pdf>. My copy of NFPA 79 started to grow moldy and I had to remove it from under my pillow.
I’m not sure I have much to add to the discussion. I believe the guidance given by Mr. Nyffenegger is correct and Mr. O’Connell has given accurate additional information. Ted Eckert Microsoft Corporation The opinions expressed are my own and do not necessarily reflect those of my employer, the NFPA, ASHRAE, IEC TC108 or the International Brotherhood of Motor Thermal Protection Design and Installation Engineers (IBMTPDIE). -----Original Message----- From: Brian O'Connell [mailto:oconne...@tamuracorp.com] Sent: Friday, March 10, 2017 11:35 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Moter Overload Protection with Supplemental Protector Ted Eckert could probably answer this more completely, as has been rumored that he sleeps with a copy of NFPA79 beneath pillow, and has his phone configured where 911 auto-dials members of TC108. Motor protection - inverse time breaker sized to 250% of FLC, see table 430.52; but for 1/2 hp, NEC wants 14 awg in the raceway. FLC should be per tables 430.247, 430.248, 430.250, 430.6(A)(1). FLA is per the motor's nameplate rating; and is used to determine conductor requirements per 430.22 and branch ckt overcurrent sizing per 430.52 and 430.62. If motor indicates FLC on nameplate, ignore the HP rating and use FLC number. As both of your scenarios are powered from OC-protected branch ckt, 'supplemental' current interrupt devices would be ok per code, but would not recommend for some motors. If you are wired into a 'derived' ckt, you would also need to assess the limits of the materials. Branch ckt protection devices are for short ckt only - they should not be intended to protect for motor overloads. Probably preaching to choir, but article 240 is *not* scoped for motors, and many do not want to use article 430 to avoid the bigger FLA and FLC current protection requirements. Brian -----Original Message----- From: Kunde, Brian [mailto:brian_ku...@lecotc.com] Sent: Friday, March 10, 2017 10:49 AM To: EMC-PSTC@LISTSERV.IEEE.ORG<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> Subject: [PSES] Moter Overload Protection with Supplemental Protector Greetings experts. This question applies to both North America rules (NEC) keeping in mind the rest of the world including Europe BUT my example will be for a 115Vac 60hz device. My example product is used in the Workplace but not typically in an industrial environment (if that matters). It's not a home appliance or power tool. Consider an End Product powered by 115Vac 60hz from a standard 16AWG power cord with a NEMA-5-15 plug, from a 15 amp receptacle (15 amp Branch Circuit). Within this product is a 1/2 hp motor with an Full-Load Amp (FLA) rating of 5 amp. The motor can run continuous in this application. The motor does not have integrated over temperature protection. Scenario 1: If this was a single phase AC motor, we would have to provide Overload Protection. According to the NEC, a fuse or circuit breaker no larger than 6.25 amp (FLA x 125%) can be used (lets ignore start up current for now). Can this Overload Protector be a "Supplemental Protector" (UL 1077 circuit breaker) or does it have to be a UL 489 circuit breaker or some other type of device? Scenario 2: If an Inverter, Frequency Drive, PWM Motor Controller, etc. is used to drive an AC or PWM DC motor (1/2hp), the Branch Circuit is not stressed by Motor Start currents since the motor is soft started. So for example, if we have a 1/2hp 90Vdc motor that is driven by a PWM controller, can the Overload Protector be a Supplemental Protector? If not, what does it have to be and why? Scenario 3: If the inverter, frequency drive, PWN motor controller, etc. provides Overload Protection for the motor, do we even need to add an additional Overload protector? Can we use a single Supplemental protector for the entire product and not worry about the motor? In this scenario, I assume the motor controller would have to be Listed by a safety agency and specifically call out the overload protection feature in the datasheet. What other concerns might I need to know about? I'm trying to make sense of the NEC article 430 but it doesn't seem to address motors driven by Motor Controllers. Can I assume that when a motor is driven by a Motor Controller (inverter, freq. drive, PWM, etc.) that the NEC 430 does not apply because the motor is not being directly powered by a Branch Circuit? Thanks to all in advance. 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. 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