110.24
- Thread starter dre120
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kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
That is new section in 2011 NEC.
If they have not gotten used to installers asking about it then you have just recently adopted the 2011, or the inspectors have not been enforcing that new section.
I get funny looks from them sometimes myself, and generally just find out what size their transformer is and the impedance and do calculations myself. This will not necessarily give accurate results, but instead a worst case result. If your equipment can handle worst case then it should be safe. When you get results that are close to max equipment ratings you must then either get higher rated equipment or get more serious about accuracy.
Most basic calculations assume infinite transformer supply capabilities when in reality there is limits to the supply, (distance and size of conductors to substation, and the impedance of the sub as well as the incoming supply to the sub are also factors) so most instances the calculation results in worst case scenario assuming infinite supply at the transformer supply terminals.
If they have not gotten used to installers asking about it then you have just recently adopted the 2011, or the inspectors have not been enforcing that new section.
I get funny looks from them sometimes myself, and generally just find out what size their transformer is and the impedance and do calculations myself. This will not necessarily give accurate results, but instead a worst case result. If your equipment can handle worst case then it should be safe. When you get results that are close to max equipment ratings you must then either get higher rated equipment or get more serious about accuracy.
Most basic calculations assume infinite transformer supply capabilities when in reality there is limits to the supply, (distance and size of conductors to substation, and the impedance of the sub as well as the incoming supply to the sub are also factors) so most instances the calculation results in worst case scenario assuming infinite supply at the transformer supply terminals.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
It's a new requirement in the 2011 code to mark service equipment with the available fault current. The utility should have that information, if they own the transformer, even if they were unaware that anyone would be asking for it. It does not apply to dwelling units.
There are circumstances where the utility would not have the information. For example, if the service transformer is the property of the building owner, and if the service connection point is upstream of the transformer, then someone will have to perform the fault current calculation.
There are circumstances where the utility would not have the information. For example, if the service transformer is the property of the building owner, and if the service connection point is upstream of the transformer, then someone will have to perform the fault current calculation.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Your 25k panel is fine, but next thing you would need to know if still questionable is at what point is the 10146? Transformer output terminals? At the meter socket? Any conductor beyond the point that applies will yield a lower level at the load end because of the resistance of that conductor. Sometimes just 15 or 20 feet of conductor makes a big difference.
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