Fault currents motor contribution

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don_resqcapt19 said:
If you need real numbers, you need someone to run the system in one of the electrical engineering software programs...everything else is just a good guess.
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If I say to provide using electrical engineering software they can just get any software or anything from internet and do this study.
 
hhsting said:
Take a look at NEC 110.9 and 110.10 and 240.86 first paragraph and part C. Thats why. You cant get that without short circuit w motor contribution.
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So where that is required, you make the design engineer provide the required information, and unless you have very solid reasons to doubt what has been provide, you just use that information. If your permitting process does not require that type of information, you just comment on the plans that this may not be in compliance with the rules in the NEC.
 
jim dungar said:
Then why are you questioning it?

Designers often use simplified techniques and then specify a through study as part of the project contract.
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I didn’t find it but Why do designers do that? How does that work with AHJ and approving plans? study happens after approval of plans?
 
don_resqcapt19 said:
So where that is required, you make the design engineer provide the required information, and unless you have very solid reasons to doubt what has been provide, you just use that information. If your permitting process does not require that type of information, you just comment on the plans that this may not be in compliance with the rules in the NEC.
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What?! Permitting process require to follow NEC 2017. Yea solid reason is it can be way off, loose estimate
 
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hhsting said:
...study happens after approval of plans?
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Yes.
The official study occurs after the project has been started.

It is very common to have the short circuit study identify design short comings resulting in changes to equipment that has already been approved, order, and sometimes installed. The AHJ looks at the study as part of their final approval.
 
jim dungar said:
Yes.
The official study occurs after the project has been started.

It is very common to have the short circuit study identify design short comings resulting in changes to equipment that has already been approved, order, and sometimes installed. The AHJ looks at the study as part of their final approval.
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Exactly who in AHJ looks at the study as part of final approval reviewers, inspectors who?
 
hhsting said:
Exactly who in AHJ looks at the study as part of final approval reviewers, inspectors who?
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I really don't know.
My studies were usually provided as part of the final deliverables before an occupancy permit was provided. Occasionally they were done early enough in the project to be included with the electrical contractor's approval drawing submittal. All of which occurred well after the 'building' department's plan review.
 
hhsting said:
What?! Permitting process require to follow NEC 2017. Yea solid reason is it can be way off, loose estimate
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Lots of things in a permitting process are not found in the NEC such as a requirement to provide a fault current study as part of the permit application.
In many cases, they cannot be complete until after the project has been installed as the actual conductor lengths makes a difference in the fault current. At the design stage, the designer would typically use a conservative estimate and that is all you really need for plan review.
You just use what has been provided and require changes after the fact if there is an issue after completion.

I would just note on the plans, that they are approved pending the final, after installation, short circuit study, and that if the equipment is not in compliance at that time, it will have to be replaced. This will give enough push to the owner, designer, and installer to be sure that the original installation is compliant.
 
don_resqcapt19 said:
Lots of things in a permitting process are not found in the NEC such as a requirement to provide a fault current study as part of the permit application.
In many cases, they cannot be complete until after the project has been installed as the actual conductor lengths makes a difference in the fault current. At the design stage, the designer would typically use a conservative estimate and that is all you really need for plan review.
You just use what has been provided and require changes after the fact if there is an issue after completion.

I would just note on the plans, that they are approved pending the final, after installation, short circuit study, and that if the equipment is not in compliance at that time, it will have to be replaced. This will give enough push to the owner, designer, and installer to be sure that the original installation is compliant.
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110.9 and 110.10, 240.86(c) first paragraph all of them NEC 2017 version require fault current calculations. I am not sure where you are getting its not in NEC?
 
hhsting said:
110.9 and 110.10, 240.86(c) first paragraph all of them NEC 2017 version require fault current calculations. I am not sure where you are getting its not in NEC?
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While those sections do require the calculations, nothing in those sections requires the calculation be made available to the inspection authority as part of the permit process.

You are asking for information that the NEC does not require the engineer to provide. There are some rules where the code requires calculations to be made available to the AHJ, those sections do not.

If you want that information to be provided with the plans submitted for plan review, your local permit ordinance must specify that the short circuit study be supplied along with the plans and specifications when they are submitted for review.
 
don_resqcapt19 said:
While those sections do require the calculations, nothing in those sections requires the calculation be made available to the inspection authority as part of the permit process.

You are asking for information that the NEC does not require the engineer to provide. There are some rules where the code requires calculations to be made available to the AHJ, those sections do not.

If you want that information to be provided with the plans submitted for plan review, your local permit ordinance must specify that the short circuit study be supplied along with the plans and specifications when they are submitted for review.
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Which sections require calculation?

Also I still dont follow how you can say those section dont require fault current calculation. Interrupt rating must be greater than available fault current. If they dont provide interrupt rating at all and they dont provide fault current calculation then how do I know if NEC 2017 section 110.9 or 110.10 comply? I cannot do that without fault current calculation that is saying short circuit fault current calculation

NEC 2017 section 240.86 first paragraph in order to verify if it applies say available fault current must be greater than interrupt rating. NEC 2017 section 240.86(C) says higher rated device and lower rated deci e how do I know if all that applies if fault current calculations and interrupt rating not provided?


Remember this is a high rise and also this is brand new building.
 
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hhsting said:
Which sections require calculation?

Also I still dont follow how you can say those section dont require fault current calculation. Interrupt rating must be greater than available fault current. If they dont provide interrupt rating at all and they dont provide fault current calculation then how do I know if NEC 2017 section 110.9 or 110.10 comply? I cannot do that without fault current calculation that is saying short circuit fault current calculation

NEC 2017 section 240.86 first paragraph in order to verify if it applies say available fault current must be greater than interrupt rating. NEC 2017 section 240.86(C) says higher rated device and lower rated deci e how do I know if all that applies if fault current calculations and interrupt rating not provided?


Remember this is a high rise and also this is brand new building.
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NEC 2017 section 110.9:

110.9 Interrupting Rating.

Equipment intended to interrupt current at fault levels shall have an interrupting rating at nominal circuit voltage at least equal to the current that is available at the line terminals of the equipment.

Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage at least equal to the current that must be interrupted.

NEC 2017 section 110.10:

110.10 Circuit Impedance, Short-Circuit Current Ratings, and Other Characteristics.

The overcurrent protective devices, the total impedance, the equipment short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit protective devices used to clear a fault to do so without extensive damage to the electrical equipment of the circuit. This fault shall be assumed to be either between two or more of the circuit conductors or between any circuit conductor and the equipment grounding conductor(s) permitted in 250.118. Listed equipment applied in accordance with their listing shall be considered to meet the requirements of this section.


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hhsting said:
Which sections require calculation?

Also I still dont follow how you can say those section dont require fault current calculation. Interrupt rating must be greater than available fault current. If they dont provide interrupt rating at all and they dont provide fault current calculation then how do I know if NEC 2017 section 110.9 or 110.10 comply? I cannot do that without fault current calculation that is saying short circuit fault current calculation

NEC 2017 section 240.86 first paragraph in order to verify if it applies say available fault current must be greater than interrupt rating. NEC 2017 section 240.86(C) says higher rated device and lower rated deci e how do I know if all that applies if fault current calculations and interrupt rating not provided?


Remember this is a high rise and also this is brand new building.
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You are not reading what I am saying. I have never said that the calculations are not required.

All I am saying is that the NEC does not require those calculation to be provided to you as part of the permit process. If you want those to be provided, your local ordinance that covers permit applications must specifically require that the person or company requesting the permit provide you with those calculations.
 
don_resqcapt19 said:
You are not reading what I am saying. I have never said that the calculations are not required.

All I am saying is that the NEC does not require those calculation to be provided to you as part of the permit process. If you want those to be provided, your local ordinance that covers permit applications must specifically require that the person or company requesting the permit provide you with those calculations.
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Well if AHJ building plan review has adopted NEC so this means as part of permit process AHJ is to check the plans against whats in NEC to see if plans comply or not and NEC requires calculation then how do you say NEC does not require those calculation to be provided as part of permit process?

I apologize but I am having hard time understanding. I really appreciate your help and patience
 
hhsting said:
Well if AHJ building plan review has adopted NEC so this means as part of permit process AHJ is to check the plans against whats in NEC to see if plans comply or not and NEC requires calculation then how do you say NEC does not require those calculation to be provided as part of permit process?

I apologize but I am having hard time understanding. I really appreciate your help and patience
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Sections 110.9 or 110.10 do not require "calculations", they simply require that equipment/devices are properly applied. Calculations are one method to demonstrate compliance. Based on this thread (in addition to what I already explained to you in the DM), I believe your questions have been thoroughly answered. Whether you agree or want to accept it is another issue altogether.
 
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