# Utility Transformer Fault Current



## jar546 (Nov 24, 2018)

Based on the POCO transformer dataplate seen below, what is the fault current that you would expect at the line terminals of the service disconnect?  Please answer Line to Line and Line to Neutral.


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## chris kennedy (Nov 25, 2018)

We can tell you fault current at tranny secondary bushings but for the service disconnect need to know wire size and length between the two.


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## ICE (Nov 25, 2018)

chris kennedy said:


> We can tell you fault current at tranny secondary bushings but for the service disconnect need to know wire size and length between the two.


I’m pretty sure that “we” Is a party of two.


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## jar546 (Nov 25, 2018)

chris kennedy said:


> We can tell you fault current at tranny secondary bushings but for the service disconnect need to know wire size and length between the two.



You ruin everything with trick questions!

So after we figure the fault current at the secondary taps, what is it at the service disconnect if the run is parallel (2) 350's @ 50'?


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## jar546 (Nov 25, 2018)

ICE said:


> I’m pretty sure that “we” Is a party of two.



Lots of commercial electrical inspectors know and should know how to do this since it is part of plan review.


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## ICE (Nov 25, 2018)

Jeff,
Maybe one in a hundred commercial electrical inspectors have the knowledge that you do. It's not that it is so complicated but rather that they have not been exposed to the formula. I for one would never need to know. Not that it would never come up during an inspection but because I ask for the number and run it by my electrical engineer.

So be a Peach and tell us how to do it.

Thanks in advance


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## jar546 (Nov 25, 2018)

ICE said:


> Jeff,
> Maybe one in a hundred commercial electrical inspectors have the knowledge that you do. It's not that it is so complicated but rather that they have not been exposed to the formula. I for one would never need to know. Not that it would never come up during an inspection but because I ask for the number and run it by my electrical engineer.
> 
> So be a Peach and tell us how to do it.
> ...



This is actually somewhat of a repeat:  https://www.thebuildingcodeforum.com/forum/threads/calculating-fault-current.24172/


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## ICE (Nov 25, 2018)

jar546 said:


> This is actually somewhat of a repeat:  https://www.thebuildingcodeforum.com/forum/threads/calculating-fault-current.24172/


Well there's no phone number on this label so I can't be much help here.


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## steveray (Nov 26, 2018)

110.24.....But that is as far as I go, make the engineer do the calcs...


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## jar546 (Nov 26, 2018)

There isn't always an engineer needed for every transformer swap, or electrical job.


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## ICE (Nov 26, 2018)

jar546 said:


> There isn't always an engineer needed for every transformer swap, or electrical job.


My jurisdiction has combination inspectors.  We are tasked with all of the codes.  I know enough to ask when I know that I don't know.  

None of us are supposed to inspect a transformer that was not plan checked by our electrical engineers.  We seldom see a transformer installation.  It takes the burden from the inspector....an inspector that has plenty to do.....an inspector that just came from a re-roof inspection and has new house, framing and all of the roughs, up next.  Add to that the experience level that abounds here and ....well thank goodness that we have the engineers.


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## jar546 (Nov 26, 2018)

ICE said:


> My jurisdiction has combination inspectors.  We are tasked with all of the codes.  I know enough to ask when I know that I don't know.
> 
> None of us are supposed to inspect a transformer that was not plan checked by our electrical engineers.  We seldom see a transformer installation.  It takes the burden from the inspector....an inspector that has plenty to do.....an inspector that just came from a re-roof inspection and has new house, framing and all of the roughs, up next.  Add to that the experience level that abounds here and ....well thank goodness that we have the engineers.



Most inspection departments/agencies do not have the luxury of an in house engineer.  I guess you are lucky.


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## ICE (Nov 26, 2018)

jar546 said:


> Most inspection departments/agencies do not have the luxury of an in house engineer.  I guess you are lucky.


We have all kinds..... in the dozens.  If it was left up to the administration, there wouldn't be anything but engineers.


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## steveray (Nov 27, 2018)

jar546 said:


> There isn't always an engineer needed for every transformer swap, or electrical job.


Then if the electrician wants to show me his calcs, I would be happy to review them....


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