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 Post subject: Arc Flash Potential?
PostPosted: Mon Nov 29, 2010 1:03 pm 
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We have created a portable temporary power system - supply is 480V/10A single phase into a toroid transformer, output is 120VAC/40A.

The components are enclosed in a NEMA 1 aluminum enclosure. The interfaces on the front panel are standard 120V electrical outlets. What is the potential for an arc flash with this equipment? I can provide a schematic if necessary. Here is a picture of the system. Each unit has a 480V/120V Xfmr.

Thanks.


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PostPosted: Tue Nov 30, 2010 8:05 am 
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Since this is single phase, with a 10 A feed this would not fall into a IEEE 1584 analysis. What is your company's standard electrical PPE requirements?
If it is HRC #1 PPE, I would think that would be sufficient.

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PostPosted: Tue Nov 30, 2010 8:45 am 
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The workers actually plugging equipment in to the 120V outlets are not 'qualified electrical workers' per our requirements, so they don't wear HRC 1PPE. However, this is used in a radiological area so the users are wearing protective clothing which includes rubber gloves and rubber booties.

If I understand you correctly, the system power specifications are below the IEEE1584 requirements? Can you direct me to a link that states the requirements? Is it below 1KV, or is it because it's single phase?

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PostPosted: Tue Nov 30, 2010 9:13 am 
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The Equations in IEEE 1584 are for three phase circuits only and not for single phase.

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PostPosted: Tue Nov 30, 2010 9:23 am 
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Thanks for the response. So (and I apologize if I seem obtuse), this system is not capable of an arc flash?


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PostPosted: Tue Nov 30, 2010 2:44 pm 
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The system still will cause Arc flash hazard, but it will be low enough so that you can wear basic PPE to protect yourself.


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PostPosted: Tue Nov 30, 2010 3:38 pm 
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I agree that the 120 volt side would likely have a very low arc flash incident energy, but what is the 480 volt source? There may be an arc hazard on the 480 volt side. This depends entirely on the source and its overcurrent protection. Just because the source is single phase and can't be calculated using IEEE 1584 doesn't mean there is no hazard.


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PostPosted: Wed Dec 01, 2010 5:29 am 
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The 480V source is one phase (i.e. A-B) of a 3 phase 480V supply. Each phase is fused at 60 Amps at the source. However, in this system each phase is fused again at 15 Amps. The toroid transformer is only capable of drawing 10 Amps max on the 480V side. There are no copper bars in the system. Each connection employs insulated wiring. I have attached a schematic for reference.


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PostPosted: Thu Dec 02, 2010 11:57 am 
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[font="Comic Sans MS"][SIZE="4"]Am I assuming correctly that the outlet is a cover mount that is like a typical 120v outlet (the cover remains closed)? If there is no exposure to the 480v/120v wiring by these unqualified people, I doubt it would be any more than HRC 0 for them, HRC 1 for those who would service it. You may need to post an SOP cautioning people to not plug in equipment with its power on though.[/size][/font]


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