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 Post subject: Flash Hazard for Mobile Equipment?
PostPosted: Sun Dec 06, 2009 5:51 am 
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Joined: Sun Dec 06, 2009 5:39 am
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Greetings,
Does anyone know what the flash hazard requirements are for large diesel generator powered mobile equipment like impact rock crusher/jaw crushers? There are electrical components that operate at 480 volts. Is a study required? Warning labels? Is this clearly defined in 70E or anywhere else?

Please advise.
Thanks


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PostPosted: Sun Dec 06, 2009 8:45 am 
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Location: NY
Rock Crushers

Interesting point. Article 90.2 (B) (NOT Covered) item 2 states ".....Installations underground in mines AND self propelled mobile surface mining machinery and its attended trailing cable..." But section A (Covered) states"....Installations of conductors and equipment that connect to the supply of electricity..."

Does operating a generator put you in the Utility ( not covered) class ? Based on this you could definately make a case for not performing a study but OSHA would cite the general duty clause if an injury were to occur.

It should be made mandatory for any company producing and selling generators to post a arc-flash label. The calculations won't change unless you sync a few together or have motors contributing. Anyway, it would be a starting point.

Jim
http://www.jpbtrainingassociates.com/


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PostPosted: Sun Dec 06, 2009 4:00 pm 
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Location: Louisville, KY
What is a utility?

I think there was an OSHA case a few years back in which OSHA was legally justified in NOT defining a generator, PPO or a Co-Gen as a utility.

The "service point" in the NESC (ANSI C2) is what defines the utility. Utilities get their legal exemptions because they have "public service" responsibilities, like keeping power on to hospitals and critical public operations and servicing rural areas. This is why they are given some leeway by congress in the public utilities act and subsequent legislation.

Make sure you are considered a utility by OSHA before using the utility exemption. Misuse of this clause is part of what is driving some to call for eliminating the exemption. it was almost eliminated in Canada Z246 and mines were not exempted. The NESC (the NFPA-70E-like standard for utilities) requires a resonable arc flash study and protection for the workers.
So even if you are a utility you don't get out of a study but might get some relaxation on labeling some equipment. Part of utility equipment can require NEC compliance.

Be sure before you exempt something from due diligence.


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PostPosted: Sun Dec 06, 2009 5:51 pm 
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Location: Charlotte, NC
"Does operating a generator put you in the Utility ( not covered) class ? Based on this you could definately make a case for not performing a study but OSHA would cite the general duty clause if an injury were to occur. "

Just because you operate a generator, that does NOT make you a utility. To qualify for that exemption, you would need to be governed by the NESC.

"It should be made mandatory for any company producing and selling generators to post a arc-flash label. The calculations won't change unless you sync a few together or have motors contributing. Anyway, it would be a starting point."

But if you sync a few together or have motor contribution OR if you have a utility contribution at its terminals, and the mfg. has no way to know. Then the label would be wrong, useless, dangerous and should not have been there to start with. :confused:


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PostPosted: Mon Dec 07, 2009 7:56 am 
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Generator's Arc Flash Label

I like the idea of the mfg putting the arc flash label on but it wouldn't help much except for working on the live generator. The cable connections is about all it would apply to. Diesel generators usually produce lower fault current than the utility system and make the whole plant have greater arc flash energies when they are running unless they are running WHEN the utility generation is running. Lots of scenarios that all require due diligence in a well designed arc flash study. We have run as many as 5 scenarios on normal plants and many more on T&D systems and power plants.


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PostPosted: Mon Dec 07, 2009 8:58 am 
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First, how large is large?

Up to ~ 200kW, I think the arc flash hazard is going to be fairly small, but a study should be done.
By the time you take the generator decrement curve and voltage drop into account, the arc flash is short lived, with reduced energies.


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PostPosted: Mon Dec 07, 2009 11:58 am 
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Thanks

Thanks for all the replies. We still will do a flash hazard study with regard to "general duty" but I am confident that NFPA 70E does not require it (not covered). However, working on this type of energized equipment definitely represents a a hazard so our study will outline all conditions, design the appropriate warning labels, identify the proper PPE and any other relevant data to try to ensure safe maintenance and operation.


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