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 Post subject: 120 VAC Voltage Testing
PostPosted: Wed Feb 06, 2013 12:36 pm 
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Hi,
I am a safety guy trying to get my company in NFPA 70E compliance and I am new to the forum. Please excuse me if this question has been answered before.
What HRC would apply for voltage testing a 120 VAC receptacle with the cover on.
Thanks,
Skip


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PostPosted: Wed Feb 06, 2013 4:33 pm 
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If your electrical system meets the requirements in the tables in 130.7 then you can use those and you are at H/RC 0. If not you can assume that anyways if you meet certain minimal requirements following IEEE 1584 currently. That section is under review and likely to be revised in the next edition. Otherwise, you pay for an engineering study and I highly recommend doing both the hazard analysis (IEEE 1584) AND the risk analysis (HAZOP, FTA, SWIF, etc.), using for instance one of the ANSI risk assessment methodologies since when you take the engineering study approach, IEEE 1584 does not address risk, only hazard.


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PostPosted: Thu Feb 07, 2013 12:48 pm 
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Thanks for the reply.
Could please look at this transformer tag and tell me the Voltage, Phase, KVA, Full Load Amps and % Impedance?
Thanks,
Skip


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PostPosted: Fri Feb 08, 2013 6:26 pm 
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13800:480Y/277 V, three phase, 1288 kVA, 1549 A secondary, 5.76%. Did I get it right? Really should start a new thread for a new question.


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PostPosted: Sat Feb 09, 2013 7:13 pm 
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You can't directly use a short circuit analysis method for arc flash modeling. Short circuit methodologies typically ignore the contribution of reactive power sources (especially motors) that can increase the available fault current over the transformer rating, and assuming "zero" impedance for cabling, bus bar, and wiring, is a typical beginners mistake. You need to model all of the impedances to determine the fault current for arc flash purposes. Which means you end up doing a full blown arc flash study. There are no short cuts here.


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PostPosted: Mon Feb 11, 2013 9:37 am 
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What am I missing:

1. Single Phase 120V.
2. A 20A overcurrent device.

Why is arc flash even being discussed (no disrespect to anyone).


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PostPosted: Mon Feb 11, 2013 7:25 pm 
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Hi Skip

As mentioned above. There is no arc flash hazard here, 120 Volt single phase. At least no flash that will cause injury. Also no exposed energized electrical parts. So no need for shock protection.

Again no disrespect, however would you wear electrical specific PPE and clothing to plug in an appliance at home


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PostPosted: Thu Feb 14, 2013 7:38 am 
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Skip

If you are the "Safety Guy" responsible for electrical safety, then you need to "demand" training to get up to speed with NFPA 70E & OSHA Subpart S standards. The pay back could be a matter of life or death. The best thing a non-electrical safety manager can do is admit they don't know that they don't know. If you can survive the impending "sales pitch" from an electrical safety consultant, then contact one and have them tell you (for free) what it will take to get you into compliance. Then take half of what they tell you and investigate the rest.


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PostPosted: Thu Feb 14, 2013 10:37 am 
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Implementing an arc flash protection program is a huge undertaking but something that must be done. Developing a committee consisting of members of the company’s electrical community, management and the safety department can also be very beneficial in conducting the required research, standards interpretation, decision making, developing procedures and training.


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PostPosted: Thu Feb 28, 2013 5:26 pm 
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Flash wrote:
What am I missing:

1. Single Phase 120V.
2. A 20A overcurrent device.

Why is arc flash even being discussed (no disrespect to anyone).


I agree...


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PostPosted: Thu Feb 28, 2013 7:09 pm 
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Flash wrote:
What am I missing:

1. Single Phase 120V.
2. A 20A overcurrent device.

Why is arc flash even being discussed (no disrespect to anyone).


1. The tables in 70E, if you haven't done an arc flash hazard study, include some H/RC 1 cases for up to 240 V panels. So sorry, can't categorically dismiss this.

2. If you used IEEE 1584 as the analysis method and meet the special criteria (currently <125 kVA single transformer) then you can say there's no appreciable arc flash hazard except when wearing meltable clothing. If however you violate those assumptions or are following the 70E tables or Ralph Lee's theoretical model, then you can easily find yourself in something above a 1.2 cal/cm^2 hazard.

3. Some recent test work by NFPA/IEEE has shown that arc flashes are possible (though extremely limited circumstances) that exceed 1.2 cal/cm^2 at these voltages. The circuit breaker obviously doesn't matter if we have an extremely large transformer and/or multiple sources connected to the load other than the fact that it can trip very quickly, especially if the work to be done is on the breaker itself where line-side exposures may exist.

So, no, you can't categorically dismiss even a "simple 120 V, 20 A breaker" case, both from a practical and theoretical point of view. Since that's all the information you've been given, you can't make assumptions about the scenario as given.


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