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 Post subject: Ultra high amps w/ medium voltage ... true hazard?
PostPosted: Mon Nov 09, 2015 5:15 am 
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Hello,

I'm new to forum and hoping one of the pros here can ease my mind a bit.

While conducting an arc flash survey I ran into a few panel and switches that are bothering me a bit. I just do not feel that I am capturing the risk properly. If I may provide a few examples below. I would like to know what you believe the HazCat is for each, so that I may compare it with mine.

Thank you in advance.

Bret


Main Panel Switch
Rating: 1200A
Syst Voltage: 120/208V
Fault Current: 100K
Grounded
w/typical defaults

Main Panel Switch
Rating: 1600A
Syst Voltage: 480V
Fault Current: 35K
Grounded
w/typical defaults

Disconnect Switch
Rating: 400A
Syst Voltage: 120/208V
Fault Current: 65K
Grounded
w/typical defaults


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 Post subject: Re: Ultra high amps w/ medium voltage ... true hazard?
PostPosted: Mon Nov 09, 2015 5:54 am 
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What incident energy was calculated for each? You can't do an arc flash assessment on an individual piece of equipment without including the upstream equipment as well.


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 Post subject: Re: Ultra high amps w/ medium voltage ... true hazard?
PostPosted: Mon Nov 09, 2015 6:07 am 
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Location: Rutland, VT
I am confused by what you mean by arc flash survey. Are you collecting data to perform an arc flash study? Also the Fault Current that you list for those devices seems to be the Short Circuit Rating. Is that true?

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 Post subject: Re: Ultra high amps w/ medium voltage ... true hazard?
PostPosted: Mon Nov 09, 2015 7:16 am 
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My first task was to go to each facility and gather information that is on the main panel which feeds the building. Each of the examples I provided was from the main. These are not for individual pieces of equipment. However, a facility in some cases may only contain a single item like a pump house.


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 Post subject: Re: Ultra high amps w/ medium voltage ... true hazard?
PostPosted: Mon Nov 09, 2015 7:28 am 
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Ok, so you have collected that data, not sure what you mean by typical defaults but there is nothing wrong with what you collected. So I am still not clear on what you are asking.

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 Post subject: Re: Ultra high amps w/ medium voltage ... true hazard?
PostPosted: Mon Nov 09, 2015 8:30 am 
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Typical defaults such as Arc Flash Boundaries and Gaps for MCC/Panels & Switch Gears, etc. ... 18"/25mm and 24"/32mm respectively. Using a .03/.33/.5 second clearing times as shown in in the 70E tables.

I was hoping to see what kind of results others came up with. Depending on the method I used the 1200A Main panel came in as either a HazCat 2 or a HazCat 4.


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 Post subject: Re: Ultra high amps w/ medium voltage ... true hazard?
PostPosted: Mon Nov 09, 2015 9:22 am 
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What is your fault current at the Main Panel and what is the upstream clearing device? That will help.

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 Post subject: Re: Ultra high amps w/ medium voltage ... true hazard?
PostPosted: Mon Nov 09, 2015 9:43 am 
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I am assuming that would information found on the transformer on the pole. Just great.


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 Post subject: Re: Ultra high amps w/ medium voltage ... true hazard?
PostPosted: Mon Nov 09, 2015 10:44 am 
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Yes and no. What you need to do is ask the utility company for:
1. Available fault current on at the primary fusing for 3 ph and SLG along with X/R
2. Primary fuse data
3. Transformer info such as size, impedance, connection
4. Riser cable although in your case it is most likely aerial conductor (quadplex)

Take that information and model it to obtain the short circuit value at your main panel. You then need to determine the corresponding fault current in the primary fuse. These 2 pieces of information will allow you to determine if you are within the parameters of the NFPA 70E-2015 tables.

It sounds like you are very new to arc flash and you would benefit, IMHO, from obtaining the book, "Complete Guide to Arc Flash Hazard Calculation Studies" by Jim Phillips, PE and read it completely.

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 Post subject: Re: Ultra high amps w/ medium voltage ... true hazard?
PostPosted: Mon Nov 09, 2015 12:13 pm 
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Thank you very much!


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