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PEC vs AS/NZS vs NEC: Three Philosophies, One Physics

Ampacity plus voltage drop, temperature derating, grouping correction — the underlying physics is identical across all three codes. Here is what actually differs.

Work across the Philippine Electrical Code, AS/NZS 3008.1.1, and the NEC long enough, and a pattern becomes clear: the underlying physics governing cable sizing is completely identical across all three. What differs is reference data, presentation, and a handful of specific conventions — not the engineering itself.

What's Genuinely Identical

• The two-check structure — ampacity and voltage drop are checked independently, and the larger required conductor size wins, under every one of the three codes
• Temperature derating logic — capacity falls as ambient temperature rises above each table's own reference point, in every code
• Grouping derating logic — more current-carrying conductors sharing a raceway means more mutual heating and lower per-conductor capacity, in every code
• PV-specific safety margins — all three apply some form of a ~1.25× multiplier to a module's Isc before sizing DC cable, reflecting the same real-world overshoot above STC ratings

What Genuinely Differs

Difference	Detail
Reference tables	Independently derived datasets — PEC, AS/NZS 3008.1.1, and NEC Table 310.15(B)(16) don't share numbers, even for conceptually similar conductor sizes
Conductor size systems	PEC and AS/NZS use metric mm²; the NEC uses AWG transitioning to kcmil for larger sizes — not interchangeable by simple unit conversion alone, since the actual standard sizes offered don't line up one-to-one
Voltage drop enforcement	PEC and AS/NZS present limits as code requirements; the NEC frames its figures as an Informational Note, though it's widely enforced as a firm limit anyway
Table column structure	The NEC's insulation-temperature-rating columns (60/75/90°C) are a structurally different concept from how PEC and AS/NZS tables are typically organized

The Practical Discipline This Demands

Never mentally convert a result from one code to another and assume it's close enough. A conductor sized correctly under AS/NZS 3008.1.1 for a given load and length isn't automatically the right size for the same load and length under PEC or the NEC — pull the actual applicable table and run the actual applicable check, every time, for whichever code genuinely governs the project.

Compare the same load across codes directly using OhmWorks' PEC, AS/NZS, and NEC calculator tabs.

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