Question 1

What is NEC Table 310.16 used for?

Accepted Answer

NEC Table 310.16 gives the allowable ampacity for insulated conductors rated up to 2000V installed in raceways, cables, or directly in earth, with no more than 3 current-carrying conductors and a 30°C ambient temperature. Electricians use it to size wire for branch circuits, feeders, and services.

Question 2

When do I use 60°C vs 75°C vs 90°C ratings in Table 310.16?

Accepted Answer

The temperature column you use depends on the termination rating of the equipment, not the conductor insulation rating. Per NEC 110.14(C), most residential and commercial equipment is rated 60°C or 75°C. You may use the 90°C column only when both the conductor insulation AND all terminations are rated 90°C, or to apply correction and adjustment factors before sizing down to the 75°C value.

Question 3

How do I apply derating factors to Table 310.16 values?

Accepted Answer

When more than 3 current-carrying conductors share a raceway, apply the adjustment factors from NEC Table 310.15(C)(1) — for example, 4–6 conductors = 80%, 7–9 = 70%. For ambient temperatures above 30°C, apply the correction factors from NEC Table 310.15(B)(1). Apply both factors if applicable, then compare the result to the termination temperature rating.

Size	Copper (A)			Aluminum / Cu-Clad Al (A)
Size	60 °C	75 °C	90 °C	60 °C	75 °C	90 °C
#14 AWG	15	20	25	—	—	—
#12 AWG	20	25	30	—	—	—
#10 AWG	30	35	40	—	25	30
#8 AWG	40	50	55	30	40	45
#6 AWG	55	65	75	40	50	60
#4 AWG	70	85	95	55	65	75
#3 AWG	85	100	110	65	75	85
#2 AWG	95	115	130	75	90	100
#1 AWG	110	130	145	85	100	115
1/0 AWG	125	150	170	100	120	135
2/0 AWG	145	175	195	115	135	150
3/0 AWG	165	200	225	130	155	175
4/0 AWG	195	230	260	150	180	205
250 kcmil	215	255	290	170	205	230
300 kcmil	240	285	320	190	230	255
350 kcmil	260	310	350	210	250	280
400 kcmil	280	335	380	225	270	305
500 kcmil	320	380	430	260	310	350

Table 310.16 — Allowable Ampacities

Need to apply derating or correction factors?