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 Post subject: Arc Flash Calculation for Motor with Different PowerPosted: Wed Jan 14, 2015 3:07 pm

Joined: Wed Jan 14, 2015 7:43 am
Posts: 1
All,

I would like to ask for your advice whether it is possible to get the same Arc Flash hazard rating for motor with different power?
For example:
On a 480V BUS-1A, there are the following motor:
1. MTR-1: 2 HP
2. MTR-2: 20 HP
3. MTR-3: 80 HP

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 Post subject: Re: Arc Flash Calculation for Motor with Different PowerPosted: Fri Jan 16, 2015 5:05 am
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Joined: Wed May 07, 2008 5:00 pm
Posts: 863
Location: Rutland, VT
psdyn wrote:
All,

I would like to ask for your advice whether it is possible to get the same Arc Flash hazard rating for motor with different power?
For example:
On a 480V BUS-1A, there are the following motor:
1. MTR-1: 2 HP
2. MTR-2: 20 HP
3. MTR-3: 80 HP

Per IEEE 1584 only motors greater than 50hp need to be considered in an arc flash analysis. This is because above that the amount of short circuit current contribution can start to add to the incident energy. Therefore the analysis should be performed with the 80hp motor on the bus. All can be modeled also.

I would say that you probably won't see a difference with the 2hp and 20hp on line and you may see a slight increase in incident energy with the 80hp and with all 3 on line.

The caveat is if any of the motors have a non-regenerative variable drive on them. Then there is no fault current contribution from the motors.

_________________
Barry Donovan, P.E.
www.workplacesafetysolutions.com

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 Post subject: Re: Arc Flash Calculation for Motor with Different PowerPosted: Mon Jan 19, 2015 8:21 am

Joined: Sat Feb 07, 2009 9:24 am
Posts: 32
Location: Swanton, Vermont
If you are asking if the arc flash hazard calculated at the motor disconnects would be different for each then the answer is "possibly". If you are asking if the arc flash hazard at each of these bus taps (whether they have fuses or circuit breakers) would be different, the answer is "probably not". If you are referring to the motors' contribution to the fault current then see the reply by wbd.

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