#### walkrand

##### New member

- Location
- Michigan,USA

Thanks

- Thread starter walkrand
- Start date

- Location
- Michigan,USA

Thanks

http://electricalsector.eaton.com/bussmann-2018-SPD

The most recent SPD I have is based on the 2014 NEC, and the calculations are on pages 236-242.

The lastest SPD (based on the 2017 NEC) may be slightly different, but I trust the calcs are still in there. They have been for the last 20 years.

- Location
- Rutland, VT, USA

- Occupation
- Electrical Engineer, PE

In order to calculate the available bolted fault current in your system, you need to get the available fault current from the utility. When you initially ask, a customer service rep will look at a chart and provide you with the bolted fault current based on your transformer size and voltage. This is not what you want as that is based on an infinite bus. You have to be persistent and tell them that it is for arc flash.

Thanks

Do not use the equations in NFPA 70E-2018 as they are based on IEEE 1584-2002. IEEE 1584-2002 was superseded in November of 2018 by IEEE 1584-2018. This contains new equations based on more testing and will provide a more accurate incident energy value. The downside is that if you are trying to do this by hand, it is very complicated. For example: IEEE 1584-2002 had 3 pages which contained the equations which was 6 equations. IEEE 1584-2018 had 40 pages for the equations and has factors for enclosure size, electrode configuration, etc.

I have attached a page from IEEE 1584-2018 that shows the first equation to calculate the arcing currents. The math is substantial with logs and powers of 6, 5, etc.

View attachment equation.pdf

- Location
- New York, 40.7514,-73.9925

Due to grid switching and the "smart grid", power can come from lots of directions with changes / development making it hard to keep track, so they often just defer to unlimited primary calculations because they don't know at any given time which way power is flowing.IMO, the POCO ought to give you the available fault current at your POC based on their most recent sub-system short-circuit study. A call to the engineering section of the utility is in order.

- Location
- Rutland, VT, USA

- Occupation
- Electrical Engineer, PE

Depends on the sophistication of the utility system but they should be able to give you a max/min value or an average value as they need to know this information themselves to operate the system.Due to grid switching and the "smart grid", power can come from lots of directions with changes / development making it hard to keep track, so they often just defer to unlimited primary calculations because they don't know at any given time which way power is flowing.