Wire Ampacity Calculator

Calculate wire ampacity per NEC Table 310.15(B)(16) with temperature correction factors, bundling adjustments, and termination limitations. Professional tool for electrical engineers, contractors, and students.

Wire Specifications

Conductor Material *

Wire/Cable Type *

Wire Size (AWG/kcmil) *

Installation Method

Ambient Temperature (°F)

Current-Carrying Conductors

Parallel Runs

NEC References:

Table 310.15(B)(16) - Base Ampacity | Table 310.15(B)(2)(a) - Temperature Correction | Table 310.15(B)(3)(a) - Bundling Adjustment | Section 110.14(C)(1) - Termination Limits

🔌 What is Wire Ampacity?

Wire ampacity is the maximum amount of electrical current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. It's a critical safety parameter that ensures electrical installations operate safely and efficiently.

🌡️ Temperature Factors

• Ambient temperature corrections
• Insulation temperature ratings
• Termination temperature limits
• Heat dissipation considerations

🔗 Installation Factors

• Number of current-carrying conductors
• Bundling and grouping effects
• Installation method variations
• Parallel conductor configurations

📊 NEC Wire Ampacity Chart - Table 310.15(B)(16)

Allowable ampacities of insulated conductors rated up to 2000 volts, not more than three current-carrying conductors in raceway, cable, or earth (directly buried)

Based on ambient temperature of 30°C (86°F) - Apply correction factors for different conditions

🟤 Copper Conductors

Wire Size	60°C (140°F) TW, UF	75°C (167°F) RHW, THW, THWN, XHHW, USE	90°C (194°F) THHN, THWN-2, XHHW-2, USE-2
14 AWG*	15	20	25
12 AWG*	20	25	30
10 AWG*	30	35	40
8 AWG	40	50	55
6 AWG	55	65	75
4 AWG	70	85	95
3 AWG	85	100	115
2 AWG	95	115	130
1 AWG	110	130	145
1/0 AWG	125	150	170
2/0 AWG	145	175	195
3/0 AWG	165	200	225
4/0 AWG	195	230	260
250 kcmil	215	255	290
300 kcmil	240	285	320
350 kcmil	260	310	350
400 kcmil	280	335	380
500 kcmil	320	380	430
600 kcmil	350	420	475
750 kcmil	400	475	535
1000 kcmil	455	545	615
1250 kcmil	495	590	665
1500 kcmil	525	625	705
2000 kcmil	555	665	750

⚪ Aluminum & Copper-Clad Aluminum Conductors

Wire Size	60°C (140°F) TW, UF	75°C (167°F) RHW, THW, THWN, XHHW, USE	90°C (194°F) THHN, THWN-2, XHHW-2, USE-2
12 AWG*	15	20	25
10 AWG*	25	30	35
8 AWG	35	40	45
6 AWG	40	50	55
4 AWG	55	65	75
3 AWG	65	75	85
2 AWG	75	90	100
1 AWG	85	100	115
1/0 AWG	100	120	135
2/0 AWG	115	135	150
3/0 AWG	130	155	175
4/0 AWG	150	180	205
250 kcmil	170	205	230
300 kcmil	195	230	260
350 kcmil	210	250	280
400 kcmil	225	270	305
500 kcmil	260	310	350
600 kcmil	285	340	385
750 kcmil	320	385	435
1000 kcmil	375	445	500
1250 kcmil	405	485	545
1500 kcmil	435	520	585
2000 kcmil	470	560	630

🌡️ Temperature Correction Factors

For ambient temperatures other than 30°C (86°F), multiply the ampacities above by the appropriate factor

Ambient Temperature	60°C Rating	75°C Rating	90°C Rating
21-25°C (70-77°F)	1.08	1.05	1.04
26-30°C (78-86°F)	1.00	1.00	1.00
31-35°C (87-95°F)	0.91	0.94	0.96
36-40°C (96-104°F)	0.82	0.88	0.91
41-45°C (105-113°F)	0.71	0.82	0.87
46-50°C (114-122°F)	0.58	0.75	0.82
51-55°C (123-131°F)	0.41	0.67	0.76

🔗 Bundling Adjustment Factors

For more than three current-carrying conductors in raceway or cable

Number of Current-Carrying Conductors	Adjustment Factor
4-6	80%
7-9	70%
10-20	50%
21-30	45%
31-40	40%
41 and above	35%

*Note: Refer to NEC 240.4(D) for conductor overcurrent protection limitations. These ampacity values are based on NEC Table 310.15(B)(16) and must be adjusted for specific installation conditions. Always consult the current NEC and local codes for the most up-to-date requirements.

📋 NEC Compliance & Standards

Key NEC References

Table 310.15(B)(16)

Allowable ampacities of insulated conductors rated up to and including 2000 volts

Table 310.15(B)(2)(a)

Ambient temperature correction factors for different temperature ratings

Table 310.15(B)(3)(a)

Adjustment factors for more than three current-carrying conductors

Section 110.14(C)(1)

Equipment termination provisions and temperature limitations

Calculation Process

1Determine base ampacity from NEC Table 310.15(B)(16)
2Apply temperature correction factor based on ambient conditions
3Apply bundling adjustment factor for conductor grouping
4Consider termination temperature limitations
5Select the most restrictive ampacity value

🔧 Wire Types & Applications

THHN/THWN-2

90°C dry and wet locations

• Most common building wire
• Excellent for conduit installations
• High temperature rating
• Moisture and heat resistant

XHHW-2

90°C dry, damp, and wet locations

• Cross-linked polyethylene insulation
• Superior moisture resistance
• Underground applications
• High ampacity ratings

USE-2/RHH/RHW-2

90°C underground and wet locations

• Underground service entrance
• Direct burial applications
• Sunlight resistant
• Heavy-duty construction

NM-B (Romex)

90°C insulation, 60°C ampacity

• Residential wiring standard
• Non-metallic sheathed cable
• Dry locations only
• Cost-effective solution

UF-B

90°C insulation, 60°C ampacity

• Underground feeder cable
• Direct burial approved
• Moisture resistant
• Outdoor applications

SER/SEU & MC

75°C service and metal-clad

• Service entrance cables
• Metal-clad assemblies
• Commercial installations
• Armored protection

💡 Practical Examples & Applications

🏠 Residential Example

Scenario: 12 AWG copper THHN in conduit, 3 conductors, 90°F ambient

Calculation:

• Base ampacity (90°C): 30A
• Temperature correction (90°F): 0.96
• Bundling adjustment (3 conductors): 1.00
• Termination limit (60°C): 20A
• Final ampacity: 20A

🏭 Commercial Example

Scenario: 4/0 AWG copper XHHW-2, 6 conductors, 104°F ambient

Calculation:

• Base ampacity (90°C): 260A
• Temperature correction (104°F): 0.91
• Bundling adjustment (6 conductors): 0.80
• Termination limit (75°C): 230A
• Final ampacity: 189A

⚠️ Important Considerations

Safety Requirements

• Always use the most restrictive ampacity
• Consider continuous load factors (125%)
• Account for voltage drop limitations
• Verify equipment termination ratings

Best Practices

• Use appropriate wire type for environment
• Consider future load growth
• Minimize conductor bundling when possible
• Ensure proper installation methods

❓ Frequently Asked Questions

What is the difference between ampacity and amperage?

Ampacity is the maximum current-carrying capacity of a conductor under specific conditions, while amperage is the actual current flowing through the conductor. Ampacity is a safety limit that should never be exceeded, whereas amperage is the measured or calculated current in the circuit.

Why do termination temperatures matter for ampacity?

Equipment terminations (breakers, switches, outlets) have temperature ratings that may be lower than the conductor's insulation rating. NEC 110.14(C)(1) requires using the lower of the conductor or termination temperature rating, which often limits the usable ampacity below the conductor's full rating.

How does ambient temperature affect wire ampacity?

Higher ambient temperatures reduce a conductor's ability to dissipate heat, requiring derating of the ampacity. NEC Table 310.15(B)(2)(a) provides correction factors for different ambient temperatures. For example, at 104°F ambient, a 90°C conductor must be derated by a factor of 0.91.

When do I need to apply bundling adjustment factors?

Bundling adjustments apply when more than three current-carrying conductors are installed together in a raceway or cable. This includes phase conductors and neutrals carrying unbalanced current, but excludes equipment grounding conductors and neutrals in balanced three-phase systems.

Can I use aluminum conductors instead of copper?

Yes, aluminum conductors are permitted by the NEC and have their own ampacity ratings in Table 310.15(B)(16). However, aluminum requires larger wire sizes to carry the same current as copper, and special installation considerations apply, including compatible terminations and proper torque specifications.

What's the difference between continuous and non-continuous loads?

Continuous loads operate for 3 hours or more and require conductors and overcurrent protection to be sized at 125% of the continuous load current. This is in addition to ampacity calculations and ensures safe operation under sustained loading conditions.

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