Okonite Cable Ampacity Calculator

Cable parameters

Voltage and conductor size are required. Everything else is optional — leave it blank and the result shows the full range across every applicable table configuration.

System voltage (V) *

Conductor size (AWG / kcmil) *

Conductor material

Cable configuration

Installation method

Shielding

Conductor temperature rating

Circuits in duct bank / burial group

Ambient temperature (°C)

Cables/conduits in air — horizontal count

Cables/conduits in air — vertical count

Configuration diagram

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Result

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Min ampacity A

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Max ampacity A

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Apparent power kVA

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Reference: correction factor tables

Okonite Tables 6-1 through 6-4 — used automatically whenever you set an ambient temperature and/or a cable/conduit group size above. Shown here in full for reference and verification.

Table 6-1 — Correction factors for various ambient air temperatures (base 40°C) —

Conductor temp.	30°C	35°C	40°C	45°C	50°C
75°C	0.97	0.92	0.86	0.79	0.72
85°C	1.06	1.01	0.96	0.90	0.84
90°C	1.10	1.05	1.00	0.95	0.89
100°C	1.17	1.12	1.08	1.03	0.98
105°C	1.20	1.16	1.11	1.07	1.03
110°C	1.23	1.19	1.15	1.11	1.06
125°C	1.31	1.27	1.24	1.20	1.16
130°C	1.33	1.30	1.27	1.23	1.19
140°C	1.38	1.35	1.32	1.28	1.25

Applies to in-air and in-conduit-in-air installs (Tables 6-20 through 6-24). This calculator interpolates between columns for the 90°C and 105°C rows.

Table 6-2 — Correction factors for various ambient earth temperatures (base 20°C) —

Conductor temp.	10°C	15°C	20°C	25°C	30°C
75°C	0.99	0.95	0.91	0.87	0.82
85°C	1.04	1.02	0.97	0.93	0.89
90°C	1.07	1.04	1.00	0.96	0.93
100°C	1.12	1.09	1.05	1.02	0.98
105°C	1.14	1.11	1.08	1.05	1.01
110°C	1.16	1.13	1.10	1.07	1.04
125°C	1.22	1.19	1.16	1.14	1.11
130°C	1.24	1.21	1.18	1.16	1.13
140°C	1.27	1.24	1.22	1.19	1.17

Applies to underground duct-bank and direct-burial installs (Tables 6-5 through 6-19). This calculator interpolates between columns for the 90°C and 105°C rows.

Table 6-3 — Group correction factors: number of cables in air —

Vertical \ Horizontal	1	2	3	4	5	6
1	1.00	0.93	0.87	0.84	0.83	0.82
2	0.89	0.83	0.79	0.76	0.75	0.74
3	0.80	0.76	0.72	0.70	0.69	0.68

Applies when cables are on a messenger/support in air (Tables 6-20 through 6-22), spaced no more than one cable diameter apart. Based on a single isolated cable at 1.00.

Table 6-4 — Group correction factors: number of conduits in air —

Vertical \ Horizontal	1	2	3	4	5	6
1	1.00	0.94	0.91	0.88	0.87	0.86
2	0.92	0.87	0.84	0.81	0.80	0.79
3	0.85	0.81	0.78	0.76	0.75	0.74

Applies when conductors run in isolated conduits in air (Tables 6-23, 6-24), spaced no more than one conduit diameter apart. Based on a single isolated conduit at 1.00.

Ampacity data reproduced from The Okonite Company Engineering Data for Copper and Aluminum Conductor Electrical Cables handbook, Section 6 (Tables 6-5 through 6-25), and Table 6-25 (NEC-derived 600V ampacities). Underground duct-bank and direct-burial values assume 20°C earth ambient, RHO-90 thermal resistivity, and 100% load factor, per Okonite's stated assumptions; duct-bank cables are buried 30" to the top of the duct bank on 7½" centers, and direct-buried cable groups are buried 36" deep on 7½" centers (with multiple circuits/groups separated by 24"). In-air and in-conduit-in-air values assume 40°C air ambient with any load factor from 30–100%, for a single isolated cable or conduit — the built-in group-correction option applies the correction factors from Okonite Table 6-3 (cables in air) and Table 6-4 (conduits in air). Ambient-temperature correction uses Okonite Table 6-1 (air) and Table 6-2 (earth), linearly interpolated. This tool is provided for preliminary/reference engineering use — always verify against the current published Okonite handbook and applicable code (NEC / IEEE 835 / ICEA) before final cable sizing.