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| Motor Starter MCC https://brainfiller.com/arcflashforum/viewtopic.php?f=4&t=459 |
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| Author: | jjakubin [ Wed Jun 03, 2009 5:11 am ] |
| Post subject: | Motor Starter MCC |
I performed arc flash calculation using IEEE 1584 on a 480 volt three phase motor control center (MCC) and the incident energy level exceeds 1.2 cal/cm^2. Does the calculated value negate allowing an individual to perform a circuit breaker or starter operation with the enclosure door closed at a hazard risk category 0 based on Table 10.7(C)(9)? |
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| Author: | haze10 [ Wed Jun 03, 2009 6:38 pm ] |
| Post subject: | |
Flame question? MCCs are not switchgear and outside of the intent of high energy switching devices. With doors closed there are no exposed and energized components. Hence, NO PPE is required. If you want to use HRC0 thats higher than 'none' so go ahead. |
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| Author: | jjakubin [ Thu Jun 04, 2009 7:04 am ] |
| Post subject: | |
Thanks for your reply. Correction to my original post: I'm referring to table 130.7(C)(9) under section (600v Class Motor Control Centers (MCC's) Note-2) For example, we calculated incident energies on our 15kv switchgear and the energy levels are at Catagory-2. Per Table 130.7 (C)(9) (Metal Clad Swtichgear 1kv through 38kv) insertion or removal of circuit breakers from cubicles doors opened or closed is Catagory-4. Is it acceptable for the task of insertion or removal of circuit breakers from cubicles doors opened or closed to wear catagory-2 PPE even though the table differs? If this is acceptable because of the calculated incident energy values, why would'nt the calculated energy values dictate the PPE clothing for 480v MCC's. Do we follow the table or we follow our calculations? |
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| Author: | Zog [ Thu Jun 04, 2009 8:34 am ] |
| Post subject: | |
jjakubin wrote: Thanks for your reply. Correction to my original post: I'm referring to table 130.7(C)(9) under section (600v Class Motor Control Centers (MCC's) Note-2) For example, we calculated incident energies on our 15kv switchgear and the energy levels are at Catagory-2. Per Table 130.7 (C)(9) (Metal Clad Swtichgear 1kv through 38kv) insertion or removal of circuit breakers from cubicles doors opened or closed is Catagory-4. Is it acceptable for the task of insertion or removal of circuit breakers from cubicles doors opened or closed to wear catagory-2 PPE even though the table differs? Yes, the tables are based on many assumptions and tend to fail on the safe side (More PPE). If your calculated Ei is <8cal.cm2 you can use HRC 2 doors open or closed. jjakubin wrote: If this is acceptable because of the calculated incident energy values, why would'nt the calculated energy values dictate the PPE clothing for 480v MCC's. jjakubin wrote: Do we follow the table or we follow our calculations? Calcs. |
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| Author: | haze10 [ Thu Jun 04, 2009 8:17 pm ] |
| Post subject: | |
You have your choice of following either of two methods: under IEEE 1584 you calculate the IE at the point of interest and then use one PPE for all tasks; under NFPA Task Matrix you do NOT calculate IE at the point of interest and vary that PPE according to the table for a particular task. With the Table you need to verify Isc and OCPD (overcurrent protection device) clearing times are within the limits of the NOTES. You should not be co-mingling them together as that just creates the confusion you are experiencing now. |
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