vault backup: 2025-12-03 17:11:42

conductor-sizing.md

@@ -11,9 +11,18 @@ title: Conductor Sizing
 ---
 # Conductor Sizing
 
+It is tempting to size circuit conductors
+based on overcurrent protection,
+but they are sized independently.
+
 Conductors are sized to be suitable for the load,
 overcurrent protection is sized to protect the conductors.
 
+Allowable conductor ampacity restrictions
+are not based on a wire's ability to carry current,
+they are intended to protect its insulation
+from damage due to excessive heating.
+
 ## "The 80% Rule"
 
 > [!danger]
@@ -23,7 +32,7 @@ overcurrent protection is sized to protect the conductors.
 > that isn't preceded by a section reference,
 > it is _not_ code.
 > 
-> It is my opinion that this should never be repeated,
+> It is my opinion that this one should never be repeated,
 > even as shorthand.
 
 "The 80% Rule" is a rule of thumb
@@ -31,8 +40,12 @@ referring to a common convention of several articles
 including:
 
 * [[nfpa-70_210_branch-circuits#210.19(A)(1) General.]]
+
 * [[nfpa-70_215_feeders#215.2(A)(1) General.]]
+* [[nfpa-70_215_feeders#215.3 Overcurrent Protection.]]
+
 * [[nfpa-70_430_motors#430.22 Single Motor.]]
+* [[nfpa-70_430_motors#430.51 General.]]
 
 which paraphrased states:
 
@@ -47,9 +60,9 @@ 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%.
+namely transformers, whose feeder conductors are sized at 100%[^1].
 
-![[nfpa-70_215_feeders#215.2(B)(1) Feeders Supplying Transformers.]]
+[^1]: [[nfpa-70_215_feeders#215.2(B)(1) Feeders Supplying Transformers.]]
 
 ## Branch Circuits
 
@@ -81,7 +94,7 @@ or at least was at some point in the design.
 
 ## Feeders
 
-![[nfpa-70_250_grounding-and-bonding#250.122(A) General.]]
+![[nfpa-70_250_grounding#250.122(A) General.]]
 
 Apparently in the 2026 NEC First Draft Meetings,
 Code Making Panel 5 clarified that the equipment grounding conductor (EGC)