available short circuit current at the point of service entrance

defishu

Member
Location
new york
Help, help, help.. anyone know how can we know the available short circuit current at the point of service entrance? Per 1 RCNY §4000-01, for installing over 1000kva, we will need to show this information on plan for electrical review.

The total connected load is around 3000A, 208v, 3p. Can we use 200,000A or need to request from Con-Edison? Will con-edison provide this information or how long that would usually take to get this information since the job just started?

Thanksssssss.................
 

topgone

Senior Member
Help, help, help.. anyone know how can we know the available short circuit current at the point of service entrance? Per 1 RCNY §4000-01, for installing over 1000kva, we will need to show this information on plan for electrical review.

The total connected load is around 3000A, 208v, 3p. Can we use 200,000A or need to request from Con-Edison? Will con-edison provide this information or how long that would usually take to get this information since the job just started?

Thanksssssss.................
Short answer: Call the utility and ask for the available SC at point of common coupling.
Long one: Get the specs of the transformer feeding the service, the most important are: 1) the kVA rating, 2) secondary voltage and 3) the %Z of the transformer. Solve for the fault on the secondary end using the available transformer impedance (If = FLA/%Z).
 

nickelec

Senior Member
Location
US
3000a load if you can have the utilities bring in 277/480 u could probably cut that close to half

Sent from my SM-G965U using Tapatalk
 

wbdvt

Senior Member
Location
Rutland, VT, USA
Occupation
Electrical Engineer, PE
Short answer: Call the utility and ask for the available SC at point of common coupling.
Long one: Get the specs of the transformer feeding the service, the most important are: 1) the kVA rating, 2) secondary voltage and 3) the %Z of the transformer. Solve for the fault on the secondary end using the available transformer impedance (If = FLA/%Z).
The short answer is the correct answer if the utility provides the available short circuit current on the secondaries of the transformer. Then this value needs to be used along with the impedance of the secondary conductors to calculate the available short circuit current at the service entrance equipment.

The long answer is incorrect as this will provide the infinite bus short circuit current which is different and not the same as available short circuit current.
 
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kwired

Electron manager
Location
NE Nebraska
Help, help, help.. anyone know how can we know the available short circuit current at the point of service entrance? Per 1 RCNY §4000-01, for installing over 1000kva, we will need to show this information on plan for electrical review.

The total connected load is around 3000A, 208v, 3p. Can we use 200,000A or need to request from Con-Edison? Will con-edison provide this information or how long that would usually take to get this information since the job just started?

Thanksssssss.................
Outside of your mentioned statute, NEC in recent years has required us to calculate available fault current on pretty much everything but single family dwellings anyway and make note of it at the service equipment.

Knowing kVA and impedance of the source will give you worst case scenario at terminals of the source, presumes the primary can deliver unlimited amount of power, reality the primary impedance may place additional limit on what a particular install can actually deliver. But then you also have impedance to account for between source terminals and your service equipment. Just 25 feet of conductor can make a huge difference sometimes.

There used to be a excel spreadsheet on Mike Holts main site in the free stuff section, probably still is. It makes it easy to calculate what you are looking for.
 
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