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 Post subject: Available Fault current and PPE selection
PostPosted: Sat Oct 19, 2019 3:27 pm 

Joined: Sat Oct 19, 2019 3:14 pm
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Is there a formula to determine the amount of calorie ( Clothing Rating ) needed if the available fault current is known?
For instance, if I use the bussman app and determine that at the point I am working, 32471 amps are available, how can I calculate the amount of rating in calories is needed?

In other terms, 1 cal offers protection against ________ amps of fault current

Hope I am getting my point across.....


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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Mon Oct 21, 2019 5:40 am 
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If you have calculated the fault current, then you can use the time current curve of the upstream protective device to determine the tripping time. Then you will have the two parameters needed to determine if you can use a table in NFPA 70E

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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Mon Oct 21, 2019 6:08 am 
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I have used the Bussman app myself and it is excellent. However as Barry has indicated above you need to determine the tripping time of the closest upstram overcurrent protection device whether it be fuse or circuit breaker. You can find this by looking at the time current curve drawing


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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Mon Oct 21, 2019 9:10 am 
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sparks257ai wrote:
Is there a formula to determine the amount of calorie ( Clothing Rating ) needed if the available fault current is known?
For instance, if I use the bussman app and determine that at the point I am working, 32471 amps are available, how can I calculate the amount of rating in calories is needed?

In other terms, 1 cal offers protection against ________ amps of fault current

Hope I am getting my point across.....


No there is no formula that would allow you calculate PPE calorie rating based on available fault current. Note please that in your specific example of 32471 A fault current, arcing current could vary anywhere between 15.5kA to 30kA (600V system assumed) depending on gap between conductors, electrode configuration and equipment size. Obviously the NFPA 70E table method is highly questionable and very limited at best since it does not factor in none of the above (arcing current, protection device clearing time as a function of the arcing current, equipment configuration, gap etc.)

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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Tue Oct 22, 2019 6:37 am 

Joined: Sat Oct 19, 2019 3:14 pm
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So might there ever be a consensus established for a ratio of cal/cm2 to amperage?
I understand the calculations and factors of 1584 but the relative information and knowledge
needed to apply such, by the worker in the field, is usually not available.


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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Sun Oct 27, 2019 5:08 pm 
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sparks257ai wrote:
So might there ever be a consensus established for a ratio of cal/cm2 to amperage?
I understand the calculations and factors of 1584 but the relative information and knowledge
needed to apply such, by the worker in the field, is usually not available.


I just wondered how you've arrived at the 32471A available fault current figure. I assume that' s a total fault current. Is it the maximum value combining fault current contribution both from utility and all inductive load? What's the minimum available fault current? What'ts the amount of fault current coming through upstream protection device? What's the fault X/R ratio?

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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Mon Oct 28, 2019 6:49 am 

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Just a number I threw out there for conversation........


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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Mon Oct 28, 2019 7:13 pm 
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sparks257ai wrote:
Just a number I threw out there for conversation........


I see. I just wanted bring to your attention that you need to factor in both active and reactive impedance for each power system component, contribution from the utility as well as other inductive sources (motors and generators) and determine both total available fault current as well as fault current through upstream device before you can continue on with quantitative arc flash analysis based on IEEE 1584-2018 guide. It explains reason why NFPA 70E table method as well as Bussmann and other manufacturers arc flash calculators and tools (the ones requiring only available fault current + the manufacturer protection device part number on input) are controversial in general and very limited at best.

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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Tue Oct 29, 2019 3:52 am 

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Then what do you suggest the worker use for proper ppe selection when justified energized work exists?

Keep in mind, most systems lack coordination studies


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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Tue Oct 29, 2019 6:37 am 
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sparks257ai wrote:
Then what do you suggest the worker use for proper ppe selection when justified energized work exists?

Keep in mind, most systems lack coordination studies


Perform comprehensive short circuit and arc flash hazard analysis, and make the ppe selection based on hazards in place. The work is not justified until hazards have been identified and properly addressed.

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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Wed Oct 30, 2019 3:47 am 

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I agree that is a correct procedure, in a perfect world . However in many smaller environments it may not be practical and or feasible for a study.


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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Wed Oct 30, 2019 5:42 am 
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sparks257ai wrote:
I agree that is a correct procedure, in a perfect world . However in many smaller environments it may not be practical and or feasible for a study.


I think if employers were aware of the magnitude of possible OSHA fines, they would see that a study can be very reasonable. There are many small engineering shops that can be quite reasonable for a study as they do not have large overheads like larger firms. I have seen OSHA proposed fines of upwards to $70,000 for not providing proper PPE for electrical hazards of which arc flash is one.

The other benefits that a study provides are:
1. Available fault current is known so the entrance can be labeled with per NEC
2. Any overdutied equipment is found which is an NEC and OSHA violation
3. Coordination is checked and may be able to be improved
4. Actual incident energy is determined which allows for proper PPE to be determined and may result in cost savings by not over buying PPE.
5. With the coordination study, settings may be able to be adjusted to lower the incident energy thereby increasing safety.
6. A one line is created which the facility may not have had before.

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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Fri Nov 01, 2019 6:52 am 

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All valid points and larger companies ( corporate America) recognizes such.
But the larger problems lie with the small ones.

Real life scenario
Small manufacturing company need a 400 amp breaker replaced in their switch gear
Contractor A does a assessment and the cat table of 70e can not be used and figured a additional cost of $10,000 for a coordination study and submits a bid for $12,000

Contractor B submits a bid for $2000 to replace the breaker He figures send his guy down with a 40 cal suit and all is good

It’s obvious who the manufacturer is going to give the job to


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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Fri Nov 01, 2019 11:18 am 
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and if something goes wrong the lawyers will have a field day and the employer and his insurance company will pay a lot more and still end up having to perform a study.

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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Sat Nov 02, 2019 6:01 am 

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wbd wrote:
and if something goes wrong the lawyers will have a field day and the employer and his insurance company will pay a lot more and still end up having to perform a study.


Absolutely......

So then might there ever be a NEC mandate that all new electrical systems require a full coordination study ? That would take it above the current requirements of just having the available fault current at the service posted


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 Post subject: Re: Available Fault current and PPE selection
PostPosted: Sat Nov 02, 2019 1:08 pm 
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sparks257ai wrote:
All valid points and larger companies ( corporate America) recognizes such.
But the larger problems lie with the small ones.

Real life scenario
Small manufacturing company need a 400 amp breaker replaced in their switch gear
Contractor A does a assessment and the cat table of 70e can not be used and figured a additional cost of $10,000 for a coordination study and submits a bid for $12,000

Contractor B submits a bid for $2000 to replace the breaker He figures send his guy down with a 40 cal suit and all is good

It’s obvious who the manufacturer is going to give the job to


There are ways and resources to perform short circuit analysis for free or a fraction of your projected costs. So if Contractor B can do breaker replacement for $2000 I don't see reason why to pay fortunes to contractor A


sparks257ai wrote:
So then might there ever be a NEC mandate that all new electrical systems require a full coordination study ? That would take it above the current requirements of just having the available fault current at the service posted


I would address this question to NEC group. Right now the available fault current is required but NEC requirements may and most probably will change in the future.

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