Tables and Annexes
Tables
Tables are where many exam questions are won or lost. Key tables include Chapter 9 tables (conduit fill, conductor dimensions), Table 310.16 (ampacities), Table 250.122 (equipment grounding conductor sizing), Table 430.250 (motor full-load currents), and Table 220.42/220.55 (demand factors).
Concepts to Master
- Reading tables correctly: note the column headers, the conductor insulation type, the ambient temperature basis, and whether the table is for not more than three current-carrying conductors.
- Footnotes: footnotes modify table values and are frequently tested; never ignore them.
- Annexes: Annexes are informational unless specifically referenced. Annex C (conduit fill examples), Annex D (calculation examples), and Annex E (types of construction) are commonly referenced.
- Units: tables mix inch-pound and metric; confirm which column you are reading.
Traps
- Using Table 310.16 ampacity without applying correction or adjustment factors.
- Ignoring footnotes that change the value or impose conditions.
- Treating an Annex as enforceable code text when it is informational.
- Reading the wrong column for the insulation type or temperature rating.
Worked Example
A question gives a conductor size and insulation type and asks for ampacity. Find the row for the size and the column for the insulation, then apply any correction and adjustment factors. Rule of thumb: table value first, then corrections, then compare to the overcurrent device.
Rule of Thumb
Every table answer has three steps: locate the right row and column, read the footnotes, then apply correction and adjustment factors.