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Wire Gauge Chart

Wire Size & Amp Ratings

Wire Gauge Size
60°C (140°F) NM-B, UF-B
75°C (167°F) THW, THWN, SE, USE, XHHW
90°C (194°F) THWN-2, THHN, XHHW-2, USE-2
75°C (167°F) THW, THWN, SE, USE, XHHW
90°C (194°F) XHHW-2, THHN, THWN-2
14
15
20
25
---
---
12
20
25
30
20
25
10
30
35
40
30
35
8
40
50
55
40
45
6
55
65
75
50
55
4
70
85
95
65
75
3
85
100
115
75
85
2
95
115
130
90
100
1
---
130
145
100
115
1/0
---
150
170
120
135
2/0
---
175
195
135
150
3/0
---
200
225
155
175
4/0
---
230
260
180
205
250
---
255
290
205
230
300
---
285
320
230
260
350
---
310
350
250
280
500
---
380
430
310
350
600
---
420
475
340
385
750
---
475
535
385
435
1000
---
545
615
445
500

Understanding Ampacity​

Ampacity refers to the maximum amount of electrical current a conductor can safely carry continuously without exceeding its temperature rating. It is measured in amperes (amps). Choosing the correct wire size is critical, as undersized conductors can overheat, potentially causing insulation damage or even fire hazards.

Devices and Amp Load

The total current demand of a circuit depends on both the number and type of connected electrical devices. For instance, standard household circuits are typically rated for 20 amps, while lighting circuits are often limited to 15 amps. Proper load assessment ensures the conductor can handle the expected demand safely.

How to Calculate Ampacity Requirements

To determine the required ampacity for a circuit:

  1. Add up the total wattage of all devices connected to the circuit

  2. Divide the total wattage by the system voltage (commonly 120V or 240V)

This calculation provides the estimated current (in amps). In practice, additional factors such as voltage drop and derating conditions (e.g., ambient temperature or cable bundling) should also be considered to select the appropriate conductor size.

Ampacity Calculator

Simplify complex wire ampacity calculations with FRCABLE’s convenient Online Ampacity Calculator. This intuitive calculator takes the guesswork out of electrical code compliance, ensuring you select the right conductor size for your specific application.

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