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| Arc flash Study for 5 HP motors https://brainfiller.com/arcflashforum/viewtopic.php?f=4&t=3800 |
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| Author: | yograj.s [ Wed Oct 14, 2015 9:27 pm ] |
| Post subject: | Arc flash Study for 5 HP motors |
Why in Arc flash study the motors below 5HP are not considered? Is it there any standard for that? |
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| Author: | wbd [ Thu Oct 15, 2015 3:35 am ] |
| Post subject: | Re: Arc flash Study for 5 HP motors |
It is 50hp (37kW) motors not 5hp. This is noted in IEEE 1584-2002 Clause 4.2 and larger than 50hp motors need to be considered as they can contribute to the total fault current on a bus. |
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| Author: | PaulEngr [ Thu Oct 15, 2015 8:26 pm ] |
| Post subject: | Re: Arc flash Study for 5 HP motors |
Large motors (over 50 HP) are inductors which store energy in their magnetic fields. During a fault, they become generators for a short period of time and increase the fault current. Small motors are too small to have enough energy to make a substantial contribution so they are ignored. Second consideration and this is more of a practical one is that the overcurrent protection for a small motor will limit the incident energy to an acceptable level. Generally this holds true for breakers that are 100 A or smaller where the cable is less than 200-300 feet long and the voltage is 480 V. But I know of no detailed, published scientific study or engineering standard stating this. |
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