In the 2026 National Electrical Code, a slight revision was made that can effect which conductor or cable assembly that can be installed in accordance with the 83% rules. The revised requirements can be found in section 310.12.
This rule permits conductors for services or feeders that serve the entire load of an individual dwelling unit to be sized at not less than 83 percent of the rating of the overcurrent protective device (OCPD). Simple math would look like this. 100-amp circuit breaker equals 83-amp copper or aluminum conductors.
If you look in that section you can find Table 310.12(A) which basically does the math for us for copper or aluminum and copper-clad aluminum (CCA). This rule was introduced many years ago because of “load diversity”, which is associated with power consumption in dwellings.
We all know that not every load is going to be on at the same time within a dwelling. Therefore, we are permitted to use a reduced size service or feeder conductor for the dwelling units, but only for dwelling units.
