IEEE 1584 exception for transformers <125kVA

[shoaib10]

Hello,

This is my first question here.I am doing a short circuit and Arcflash study for a complex using SKM.I have seen articles where it says that we dont have to do arcflash for panels if they are fed from a transformer <125kVA according to IEEE std.Does the latest IEEE std still has the exception for this?

 

[jim dungar]

Hello,

This is my first question here.I am doing a short circuit and Arcflash study for a complex using SKM.I have seen articles where it says that we dont have to do arcflash for panels if they are fed from a transformer <125kVA according to IEEE std.Does the latest IEEE std still has the exception for this?

There is no formula that works well for these small circuits, so IEEE suggests that the incident energy does not need to calculated. NFPA70E does not say you can ignore these circuits. You still need to risk assess them using methodologies other than IEEE. Maybe you can use the 'task tables' in 70E.

 

[Tshering]

The IEEE 1584 2002 Edition is the latest standard, that has complete arc flash equations. There are some changes like 1584a 2004 amendment 1, 1584b 2011 amendment 2, & 1584.1 2013, but until IEEE 1584 new edition gets released, we have to use the 2002 edition equations for incident energy analysis method. Please note that the 1584 2002, section 9.3.2 exception for transformer size less than 125KVA is voltage dependent. What that means is technically:
1. For 3 phase 240V system, arc flash study has to be performed regardless of the size of the transformer.
2. For 3 phase 208V (less than 240V), arc flash study has to be performed if the service transformer is greater than 125KVA. 125 kVA transformer size is not a common standard in industry, so 112.5 KVA may be used as threshold. However, please note that recent study by IEEE 1584/NFPA 70E collaboration has shown that 208V 3 phase can actually sustain arc in the air for short circuit corresponding to transformer size relatively smaller than 125 KVA. The best way is to model in SKM/ETAP/EasyPower and run the analysis. If there is a potential thermal incident energy from 3 phase, 208V system (less than 240V), affix the label on the equipment to warn the qualified workers. At my facility, we study all 208V systems regardless of the transformer size, and label the equipment for safety.

Hello,

This is my first question here.I am doing a short circuit and Arcflash study for a complex using SKM.I have seen articles where it says that we dont have to do arcflash for panels if they are fed from a transformer <125kVA according to IEEE std.Does the latest IEEE std still has the exception for this?

 

[shoaib10]

The problem is the project i am working on has a lot of xfmrs less than 125kva...And i have to comply with the IEEE 1584 for that....If i get you right then there is no need to calculate or assess arcflash for xfmrs<125kVA according to IEEE1584.....Am i right?

 

[ron]

The problem is the project i am working on has a lot of xfmrs less than 125kva...And i have to comply with the IEEE 1584 for that....If i get you right then there is no need to calculate or assess arcflash for xfmrs<125kVA according to IEEE1584.....Am i right?

NFPA 70E still requires an arc flash label, so if you do not calculate, you would still need to determine the arc flash hazard anyway

 

[shoaib10]

Ron,

I agree that NFPA 70E states that all the equipment above 50v should be assessed for Arcflash. But the scope of work that i am doing the project on refers to IEEE 1584 so i want to make sure that i am complying with that.If the exception is still there in IEEE 1584 for xfmrs<125kVA then it would save a lot of time on my side creating the oneline...

 

[NewtonLaw]

What it means ......

What it means ......

""All equipment operating at 50 volts and higher must be assessed for electrical shock and potential ArcFlash hazards per OSHA regulations and NFPA 70E standards. IEEE 1584, published by the Institute of Electrical and Electronic Engineers (IEEE), provides a method of calculating the amount of Arc-Flash incident energy possible at certain working distances from exposed live conductors. IEEE 1584 helps to determine the Hazard Risk Category and PPE requirements of IEEE 1584 states, "Equipment below 240 V need not be considered unless it involves at least one 125 kVA or larger low-impedance transformer in its immediate power supply." This statement refers to the incident energy exposure possible under these conditions as observed during testing .

The IEEE statement means that it is not necessary to calculate incident energy on equipment under 240V fed from a transformer less than 125 kVA, because the available fault current is not high enough to sustain an Arc-Flash and release significant energy.

It is important to remember that this statement only refers to incident energy calculations, and does not release employers from the responsibility to assess all equipment operating at 50 volts and higher in the workplace for other electrical hazards, such as shock and overload conditions which may lead to electrocutions, fires, or other hazards.""

 

[shoaib10]

""All equipment operating at 50 volts and higher must be assessed for electrical shock and potential ArcFlash hazards per OSHA regulations and NFPA 70E standards. IEEE 1584, published by the Institute of Electrical and Electronic Engineers (IEEE), provides a method of calculating the amount of Arc-Flash incident energy possible at certain working distances from exposed live conductors. IEEE 1584 helps to determine the Hazard Risk Category and PPE requirements of IEEE 1584 states, "Equipment below 240 V need not be considered unless it involves at least one 125 kVA or larger low-impedance transformer in its immediate power supply." This statement refers to the incident energy exposure possible under these conditions as observed during testing .

The IEEE statement means that it is not necessary to calculate incident energy on equipment under 240V fed from a transformer less than 125 kVA, because the available fault current is not high enough to sustain an Arc-Flash and release significant energy.

It is important to remember that this statement only refers to incident energy calculations, and does not release employers from the responsibility to assess all equipment operating at 50 volts and higher in the workplace for other electrical hazards, such as shock and overload conditions which may lead to electrocutions, fires, or other hazards.""

Thanks for the clarification.One more question is that the reference from IEEE latest standard after they made the amendments or the 2002 version?

 

[wbdvt]

Thanks for the clarification.One more question is that the reference from IEEE latest standard after they made the amendments or the 2002 version?

That 125kVA statement has been in IEEE 1584-2002 since it was released. The amendments did not change that.

I always get concerned when I see threads like this about doing an arc flash study and asking questions that can be answered by reading and understanding IEEE 1584. If this is a first time doing a study, it should be done under the guidance or at least reviewed by an engineer experienced in doing the studies.

Since you are working with SKM, I assume you are familiar with it and the necessary data has been collected to input into the study. Some things to consider when doing a study are:

What to do about overdutied equipment when found?
Is it appropriate to utilize the 2 second cutoff?
Are there portions of the system that are >15kV and would require a method other than IEEE 1584 to analyze?
Are there any equipment configurations where the main breaker can be utilized in the arc flash analysis?

 

[shoaib10]

That 125kVA statement has been in IEEE 1584-2002 since it was released. The amendments did not change that.

I always get concerned when I see threads like this about doing an arc flash study and asking questions that can be answered by reading and understanding IEEE 1584. If this is a first time doing a study, it should be done under the guidance or at least reviewed by an engineer experienced in doing the studies.

Since you are working with SKM, I assume you are familiar with it and the necessary data has been collected to input into the study. Some things to consider when doing a study are:

What to do about overdutied equipment when found?
Is it appropriate to utilize the 2 second cutoff?
Are there portions of the system that are >15kV and would require a method other than IEEE 1584 to analyze?
Are there any equipment configurations where the main breaker can be utilized in the arc flash analysis?

Reason why i asked the question was i dont have a copy of IEEE 1584 and its a bit expensive to buy that....and as far as your questions are concerned the study that i am doing is to provide them with the settings so that there is no miscoordination. There are no portions in the system where the voltage is >15kV. About the overdutied equipment its not in my scope of project to analyse that but if there are any equipment they should be able to replace that with the proper equipment which can handle the amount of SC available at that equipment. And yes my work is being reviewed by the engineer....:thumbsup:

 

[wbdvt]

Reason why i asked the question was i dont have a copy of IEEE 1584 and its a bit expensive to buy that....and as far as your questions are concerned the study that i am doing is to provide them with the settings so that there is no miscoordination. There are no portions in the system where the voltage is >15kV. About the overdutied equipment its not in my scope of project to analyse that but if there are any equipment they should be able to replace that with the proper equipment which can handle the amount of SC available at that equipment. And yes my work is being reviewed by the engineer....:thumbsup:

Well, overdutied equipment will affect the arc flash results so it has to be part of your scope otherwise the employee might not be wearing the correct PPE. So are you saying that the study you are performing is only for coordination? If so, not sure why the exemption for arc flash would be a concern. However, if it is a arc flash study also, then you should consult IEEE 1584.1-2013 which is the guide for specification of scope and deliverable requirements for an arc flash hazard calculation study in accordance with IEEE Std 1584.

 

[shoaib10]

I thought IEEE 1584-2002 was their latest version with certain amendments added to it.Is 2013 version the latest?My study does have arcflash study as well....

 

[wbdvt]

IEEE 1584-2002 and its amendments 1584a & 1584b is the latest standard that provides the equations and methodology to perform the calculations to determine incident energy

IEEE 1584.1-2013 is the guide to specify what the minimum guidelines are for performing an arc flash study using IEEE 1584. The intent is to allow individuals responsible for the specification and/or performance of a study to understand the minimum scope of work and deliverables required.

 

[NewtonLaw]

Thanks for the clarification.One more question is that the reference from IEEE latest standard after they made the amendments or the 2002 version?

Yes it was.

 

[shoaib10]

Well, overdutied equipment will affect the arc flash results so it has to be part of your scope otherwise the employee might not be wearing the correct PPE. So are you saying that the study you are performing is only for coordination? If so, not sure why the exemption for arc flash would be a concern. However, if it is a arc flash study also, then you should consult IEEE 1584.1-2013 which is the guide for specification of scope and deliverable requirements for an arc flash hazard calculation study in accordance with IEEE Std 1584.

I know overdutied equipment will affect the arc flash but our scope of work is to tell them what are those equipment and the amount of SC available at that equipment.Its up to them to replace the equipment with the higher SC equipment.And as far as the exemption is concerned i still have to do the arcflash analysis for the rest of the oneline.I have many transformers < 125kVA so if it was referenced in IEEE i would communicate with the client and let him know about that....