vault backup: 2025-11-12 16:49:17

conductor-sizing.md

@@ -16,6 +16,16 @@ overcurrent protection is sized to protect the conductors.
 
 ## "The 80% Rule"
 
+> [!danger]
+> This description is provided _for reference only_.
+> 
+> Like every NEC "rule"
+> that isn't preceded by a section reference,
+> it is _not_ code.
+> 
+> It is my opinion that this should never be repeated,
+> even as shorthand.
+
 "The 80% Rule" is a rule of thumb
 referring to a common convention of several articles
 including:
@@ -36,12 +46,16 @@ and it is stated that conductors are suitable
 for 80% their listed rating,
 since 80% is the reciprocal of 125%.
 
+The rule neglects important context and common exceptions,
+namely transformers, whose feeder conductors are sized at 100%.
+
+![[nfpa-70_215_feeders#215.2(B)(1) Feeders Supplying Transformers.]]
+
 ## Branch Circuits
 
 ### Receptacle Branch
 
-> [!important]
-> There is no maximum number of receptacles per circuit _in any occupancy_.
+There is no maximum number of receptacles per circuit _in any occupancy_.
 
 It is a common misconception that the limit
 can be calculated with a formula like
@@ -67,14 +81,7 @@ or at least was at some point in the design.
 
 ## Feeders
 
-> [!cite] NEC Article 250 (emphasis added)
-> ### 250.122 Size of Equipment Grounding Conductors
-> #### (A) General.
-> Copper, aluminum, or copper-clad aluminum
-> equipment grounding conductors of the wire type
-> shall not be smaller than shown in Table 250.122,
-> but in no case shall they be required to be larger
-> than the circuit conductors supplying the equipment...
+![[nfpa-70_250_grounding-and-bonding#250.122(A) General.]]
 
 Apparently in the 2026 NEC First Draft Meetings,
 Code Making Panel 5 clarified that the equipment grounding conductor (EGC)