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 Post subject: Newbie with a very basic question
PostPosted: Thu Mar 10, 2011 6:38 pm 
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Joined: Thu Mar 10, 2011 6:24 pm
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Found the forum on a google search and looks like a lot of great information that is way over my head. A little background - I am not an electrical engineer, my background is environmental engineering and most of my 25 years has been in environmental, health & safety. I have a really basic question and you can laugh me off the forum, but at what voltage/amperage would an arc flash occur? Here's my deal, my company manages family housing at over 40 military bases in the US. We do everything for the residents but wash their dishes. Some of our maintenance techs think it's no big deal changing a breaker (15 or 20 amp) on a hot panel. Generally, the panels will be 100 amp or 200 amp. I'm pretty sure a violent explosion won't occur, but I would like to scare the crap out of these guys, before one of them gets zapped.

Thanks


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PostPosted: Fri Mar 11, 2011 6:43 am 
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ralarosa wrote:
Found the forum on a google search and looks like a lot of great information that is way over my head. A little background - I am not an electrical engineer, my background is environmental engineering and most of my 25 years has been in environmental, health & safety.

Welcome to the forum, let's start with your first question.

ralarosa wrote:
I have a really basic question and you can laugh me off the forum, but at what voltage/amperage would an arc flash occur?


That is not a basic question at all. An arc flash can occur in any system, if you unplug you vacuum cleaner at home while it is running you will see a small arc flash at the outlet. But it goes away on it's own. Where arc flash starts to become a concern is when there is enough energy behind it that it will "self sustain", meaning something (Fuse or breaker) is needed to clear the fault. Once it self sustains the duration becomes a huge factor, think of passing your hand over a candle fast vs holding it there for a few seconds.

The "generally accepted" cutoff for when an arc can be self sustaining is >208V system supplied by a >112.5kVA transformer, but there is all sorts of testing and theories that dispute that. And, that does not mean you do not need to label equipment, use safe work practices, and PPE for levels below that value.

ralarosa wrote:
Here's my deal, my company manages family housing at over 40 military bases in the US. We do everything for the residents but wash their dishes. Some of our maintenance techs think it's no big deal changing a breaker (15 or 20 amp) on a hot panel. Generally, the panels will be 100 amp or 200 amp. I'm pretty sure a violent explosion won't occur, but I would like to scare the crap out of these guys, before one of them gets zapped.


Both the NFPA 70E and OSHA do not allow for changing a breaker in an energized panel (Unless it is a critial system like at a nuclear power plant or life safety at a hospital, even then you need to use an EEWP and the proper PPE)

NFPA 70E Article 130.1 Justification for work. Live parts to which an employee might be exposed shall be put into an electrically safe work condition before an employee works on or near them, unless the employer can demonstrate that deenergizing introduces additional or increased hazards or is infeasible due to equipment design or operational limitations.

It sounds like you have some problems, and the place to start would be proper training. Employees need to be "qualified" per OSHA and 70E definitions. And by the sound of it, they are not.

According to the NFPA 70E, a “Qualified Person" is one who is trained and knowledgeable of the construction and operation of the equipment or the specific work method, and be trained to recognize the hazards present with respect to that equipment or work method.

Such persons shall also be familiar with the use of the precautionary techniques, personal protective equipment, insulating and shielding materials, and insulated tools and test equipment. A person can be considered qualified with respect to certain tasks but still be unqualified for others.

An employee that is undergoing on the job training and who, in the course of such training, has demonstrated the ability to perform duties safely at his or her level of training and who is under the direct supervision of a qualified person shall be considered to be a qualified person for the performance of those duties.

In addition, to be permitted to work within the limited approach of exposed energized conductors and circuit parts the person shall be trained in all of the following:
Qualified employees shall be trained and competent in:
•The skills and techniques necessary to distinguish exposed live parts from other parts of electric equipment
•The skills and techniques necessary to determine the nominal voltage of exposed live parts
•The minimum approach distances specified in this section corresponding to the voltages to which the qualified employee will be exposed, and,
•The decision making process necessary to determine the degree and extent of the hazard and the personal protective equipment and job planning necessary to perform the task safely


A few notes to add to the 70E definition.
•Only the employer can deem an employee qualified after they have had the proper training and have demonstrated profinency using the skills and method learned.
•There is no such thing as NFPA 70E certification, going to a training course does not make an employee qualified.
•The most misunderstood part of the "qualified" term is that it is all emcompassing, you are "qualified" to work on a specific type or piece of equipment.
•Neither a J-card, a masters license, or an engineering degree make you a "qualified person"
•The word "electrician" is not anywhere in the definition of a "qualified person" meaning these rules apply to all employees and you dont have to be an electrician to be "qualified"


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PostPosted: Fri Mar 11, 2011 7:19 am 
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Thanks for the reply. The real problem deals with supervision (or lack there of) and enforcement.


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PostPosted: Fri Mar 11, 2011 9:06 am 
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Joined: Wed Jun 24, 2009 8:47 am
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Location: Canfield, OH
NIOSH Study on electrocutions

Here is a link to a NIOSH study done on occupational electrocutions. A lot of workers like to "poo-poo" anything under 480V but Figure 10 shows that 54% of electrocutions under 600V are in the 120-240 "household voltage" range.

http://www.cdc.gov/niosh/docs/98-131/pdfs/98-131.pdf


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PostPosted: Fri Mar 11, 2011 12:46 pm 
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Thanks for the link!


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PostPosted: Tue Jan 17, 2012 5:20 pm 
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Great post, Zog. I learned a lot.


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