kwired
Electron manager
- Location
- NE Nebraska
It is extremely unlikely that the utility calculated the secondary faults for this specific installation. in most cases the utility uses lookup tables, for some utilities the value is a 'design level that will never be seen in real life (this is great for selecting the ratings of service equipment). There are some utliites that will provide L-G and L-L values for MV customers, although soemtimes we get them for 'secondary service' customers.
For equipment selection, based on SCA, there is no need to treat a center-tapped system any different than other delta. The big issue is open versus closed delta.
What happens in open vs closed delta? This is something I have similar issue as OP with myself. Need to know what fault current is on an open delta system for satisfying 110.24. I can't imagine the fault current is that high by the time the conductors hit the service disconnect that it is a problem for AIC rating, but not really sure how to figure out what difference is between open and closed delta, as well as what happens if the 120/240 pot is sized larger than the other(s).
I kind of figure a closed system should have higher level of fault current if all pots are same size, and if I maximum available current is acceptable with that then I am safe as far as not exceeding AIC rating of my equipment - but don't know what actual available current is.