Battery Equivalents and Replacements

100 Amp Wire Size: What Size Wire Do I Need For 100 Amp Service/Sub-Panel

100 Amps is a very serious current requiring thick wires in order to keep the energy losses to an acceptable level and to keep the wire surface temperature below the maximum allowed temperature.

The thickness of the wire depends on the wire material, conduit size, and maximum allowed energy losses/wire surface temperature, but it can also depend on other details, as well. Personally, if You are going to service or add 100 Amp service, consult or hire a certified electrician, regardless of whether You need a permit for such works or not.

Updated: April 24, 2024.

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AWG Wire Size Chart

The following AWG wire size chart lists some of the most common wire thicknesses with wire current carrying abilities (Wire Ampacity) and wire dimensions, given at a certain temperature:

AWG
#
Diameter
(mm/inches)
Area
(mm2/in2)
Resistance (Copper)
(mΩ/m;mΩ/ft)
Ampacity (A)
@60°C/140°F @75°C/167°F @90°C/194°F
4/0
(0000)
11.6840
0.4600
107.2193
0.1662
0.1608
0.04901
195 230 260
3/0
(000)
10.4049
0.4096
85.0288
0.1318
0.2028
0.06180
165 200 225
2/0
(00)
9.2658
0.3648
67.4309
0.1045
0.2557
0.07793
145 175 195
AWG 0 (1/0) 8.2515
0.3249
53.4751
0.0829
0.3224
0.09827
125 150 170
1 7.3481
0.2893
42.4077
0.0657
0.4066
0.1239
110 130 145
2 6.5437
0.2576
33.6308
0.0521
0.5127
0.1563
95 115 130
3 5.8273
0.2294
26.6705
0.0413
0.6465
0.1970
85 100 115
AWG 4 5.1894
0.2043
21.1506
0.0328
0.8152
0.2485
70 85 95
5 4.6213
0.1819
16.7732
0.0260
1.028
0.3133
- - -
AWG 6 4.1154
0.1620
13.3018
0.0206
1.296
0.3951
55 65 75
7 3.6649
0.1443
10.5488
0.0164
1.634
0.4982
- - -
AWG 8 3.2636
0.1285
8.3656
0.0130
2.061
0.6282
40 50 55
9 2.9064
0.1144
6.6342
0.0103
2.599
0.7921
- - -
AWG 10 2.5882
0.1019
5.2612
0.0082
3.277
0.9989
30 35 40
11 2.3048
0.0907
4.1723
0.0065
4.132
1.260
- - -
AWG 12 2.0525
0.0808
3.3088
0.0051
5.211
1.588
20 25 30
13 1.8278
0.0720
2.6240
0.0041
6.571
2.003
- - -
AWG 14 1.6277
0.0641
2.0809
0.0032
8.286
2.525
15 20 25
15 1.4495
0.0571
1.6502
0.0026
10.45
3.184
- - -
16 1.2908
0.0508
1.3087
0.0020
13.17
4.016
- - 18
17 1.1495
0.0453
1.0378
0.0016
16.61
5.064
- - -
AWG 18 1.0237
0.0403
0.8230
0.0013
20.95
6.385
10 14 16
19 0.9116
0.0359
0.6527
0.0010
26.42
8.051
- - -
20 0.8118
0.0320
0.5176
0.0008
33.31
10.15
5 11 -
21 0.7229
0.0285
0.4105
0.0006
42.00
12.80
- - -
22 0.6438
0.0253
0.3255
0.0005
52.96
16.14
3 7 -
23 0.5733
0.0226
0.2582
0.0004
66.79
20.36
- - -
24 0.5106
0.0201
0.2047
0.0003
84.22
25.67
2.1 3.5 -
25 0.4547
0.0179
0.1624
0.0003
106.2
32.37
- - -
26 0.4049
0.0159
0.1288
0.0002
133.9
40.81
1.3 2.2 -
27 0.3606
0.0142
0.1021
0.0002
168.9
51.47
- - -
28 0.3211
0.0126
0.0810
0.0001
212.9
64.90
0.83 1.4 -
29 0.2859
0.0113
0.0642
0.0001
268.5
81.84
- - -
30 0.2546
0.0100
0.0509
0.0001
338.6
103.2
0.52 0.86 -
31 0.2268
0.0089
0.0404
0.0001
426.9
130.1
- - -
32 0.2019
0.0080
0.0320
0.0000
538.3
164.1
0.32 0.53 -
33 0.1798
0.0071
0.0254
0.0000
678.8
206.9
- - -
34 0.1601
0.0063
0.0201
0.0000
856.0
260.9
0.18 0.3 -
35 0.1426
0.0056
0.0160
0.0000
1079
329.0
- - -
36 0.1270
0.0050
0.0127
0.0000
1361
414.8
- - -
37 0.1131
0.0045
0.0100
0.0000
1716
523.1
- - -
38 0.1007
0.0040
0.0080
0.0000
2164
659.6
- - -
39 0.0897
0.0035
0.0063
0.0000
2729
831.8
- - -
40 0.0799
0.0031
0.0050
0.0000
3441
1049
- - -

Note: Ampacities are given for enclosed wires @86°F (@30°C) ambient temperatures.

As one can see, the Ampacity of wires is given at three different temperatures (60°C/140°F, 75°C/167°F, and 90°C/194°F), but for most residential installations, 60°C/140°F is the maximum allowed wire surface temperature.

Also, if the value is not given for a required current, one has to look for a wire with a larger Ampacity.

For example, if we are going to look for 100 Amp wire size using default Ampacities for solid copper wire, then:

  • 60°C/140°F: 1 gauge wire (AWG 1) features an Ampacity of 115A,
  • 75°C/167°F: 3 gauge wire (AWG 3) features an Ampacity of 100A,
  • 90°C/194°F: 3 gauge wire (AWG 3) features an Ampacity of 115A.

But, these wire thicknesses are not recommended for actual use since wires should never carry current that equals their default values for safety reasons - hence the 80% Rule.

The 80% Safety Rule

80% Rule states that actual wire current should be at most 80% of its default Ampacity. Hence, we should not look for wires being able to carry 100 Amps, but 125 Amps:

I(80% Rule) = 100 Amp / 0.80 = 125 Amp

Thus, for 100 Amp service, the required wire thickness is:

  • 60°C/140°F: 0 gauge wire (AWG 0) features an Ampacity of 125A,
  • 75°C/167°F: 1 gauge wire (AWG 1) features an Ampacity of 130A,
  • 90°C/194°F: 2 gauge wire (AWG 2) features an Ampacity of 130A.

And these values are for relatively short wires, usually less than 50 feet (less than ~15 meters), which raises the question about the wire thickness of longer wires...

100 Amp Wire Length

There are several rules and standards that may be used when calculating the required wire thickness, but the general rule of thumb is to increase the required Ampacity by 10% for every 50 feet (~15 m) of the wire length - some standards increase Ampacity by 20% for every 100 feet (~30 m) which provides the same or very similar results.

For example, when calculating the required Ampacity for the 50 feet, 100 feet, 150 feet, and 200 feet wires, we can use (default value is 125 Amp, after applying the "80% Rule"):

50 feet wire: Ampacity = 125 Amps * 1.1 = 137.5 Amps

100 feet wire: Ampacity = 125 Amps * 1.2 = 150 Amps

150 feet wire: Ampacity = 125 Amps * 1.3 = 162.5 Amps

200 feet wire: Ampacity = 125 Amps * 1.4 = 175 Amps

Now, we have to check the required AWG value for given wire lengths, depending on the wire surface temperature - values are given in the following chart:

100 Amp Wire Size Chart

Wire Length / Surface Temperature @60°C/140°F 75°C/167°F 90°C/194°F
<50 feet (125 Amps) AWG 1/0 (125 Amps) AWG 1 (130 Amps) AWG 2 (130 Amps)
50 feet (137.5 Amps) AWG 2/0 (145 Amps) AWG 0 (150 Amps) AWG 1 (145 Amps)
100 feet (150 Amps) AWG 3/0 (165 Amps) AWG 0 (150 Amps) AWG 0 (170 Amps)
150 feet (162.5 Amps) AWG 3/0 (165 Amps) AWG 2/0 (175 Amps) AWG 0 (170 Amps)
200 feet (175 Amps) AWG 4/0 (195 Amps) AWG 2/0 (175 Amps) AWG 2/0 (195 Amps)

When calculating the wire thickness of the long wires, always use values from the 60°C/140°F column, since the "wire length" rule, especially after calculating the "80% Rule" is all about energy losses and not wire surface temperature - as long as the wires are properly installed.

So, if You need to know the solid copper wire thickness for 100 Amps service/sub-panel, then check the values for 60°C/140°F and sizes for such wires:

100 Amp Wire Size in mm and Inches

Wire Length AWG @60°C/140°F Diameter
(mm/in)
Area
(mm2/in2)
<50 feet (125 Amps) AWG 1/0 (125 Amps) 8.2515
0.3249
53.4751
0.0829
50 feet (137.5 Amps) AWG 2/0 (145 Amps) 9.2658
0.3648
67.4309
0.1045
100 feet (150 Amps) AWG 3/0 (165 Amps) 10.4049
0.4096
85.0288
0.1318
150 feet (162.5 Amps) AWG 3/0 (165 Amps) 10.4049
0.4096
85.0288
0.1318
200 feet (175 Amps) AWG 4/0 (195 Amps) 11.6840
0.4600
107.2193
0.1662

However, when adding or servicing a 100 Amp wire(s), it is highly recommended to consult and even hire a certified electrician who is familiar with local standards and laws regarding electric wiring. And if a permit is required, get one ...

Frequently Asked Questions (FAQ)

Here are some of the most common Frequently Asked Questions (FAQ) about 100 Amp wires and their sizes.

Can 6 gauge wire handle 100 Amps?

No, a 6 gauge wire is not suitable for handling 100 amps. For currents of this magnitude, it is typically recommended to use a wire gauge that can safely conduct the electrical load without overheating.

For 100 amps, depending on the wire length, a larger wire gauge, such as 3 gauge for copper or 1 gauge for aluminum, is generally necessary when following standard electrical codes in the United States.

It's important to select the correct wire size based on the specific requirements of your electrical circuit, including the length of the run and the ambient temperature conditions, as these factors can influence the wire's capacity to carry current safely. Always refer to the National Electrical Code (NEC) or consult with a qualified electrician to ensure safety and compliance with all local electrical codes.

What size conduit do you need for 100 amp service?

The size of conduit required for a 100 amp service depends on several factors, including the type of conduit material (e.g., PVC, EMT, RMC), the type of wire or cable, and the number of conductors in the conduit.

Here’s a general guide to help determine the appropriate conduit size for a typical 100 Amp residential service using copper wires:

  • Type of Wire: Typically, for a 100 amp service, you might use 1/0 AWG copper conductors.
  • Number of Conductors: If you are running three 1/0 AWG conductors (two hots and one neutral) and one 6 AWG ground conductor, you'll need to account for all of these in your conduit sizing.

Based on the National Electrical Code (NEC) guidelines, here are some typical conduit sizing recommendations:

  • PVC Conduit: For three 1/0 AWG conductors and one 6 AWG ground wire, you would generally need at least a 1.5-inch schedule 40 PVC conduit.
  • EMT (Electrical Metallic Tubing): A 1.5-inch EMT conduit would also be adequate for the same set of wires.
  • RMC (Rigid Metal Conduit): A 1.5-inch RMC conduit would suffice.

These sizes ensure that the conduit is not overloaded, allowing for heat dissipation and making wire pulling feasible. However, these recommendations can vary based on specific installation details and local code requirements.

Thus, it's always best to consult a certified electrician and the NEC tables and guidelines for conduit fill and check local codes or work with a qualified electrician to determine the exact needs for your specific installation.

What is the NEC code for 100 Amp service?

The National Electrical Code (NEC) provides guidelines for electrical installations, including services rated for 100 amps. However, the NEC does not specify a single "code for 100 amp service" but rather offers a series of requirements that cover various aspects of installing a 100 amp electrical service. Here are some of the key elements from the NEC that are relevant to installing a 100 Amp service:

  • Conductor Sizing: NEC Article 310 covers Conductor Types and Capacities. For 100 amp services, copper conductors need to be at least 1 AWG or larger, and aluminum or copper-clad aluminum conductors need to be at least 1/0 AWG. These sizes can vary based on the type of insulation used on the wires and the installation conditions (e.g., ambient temperature).
  • Service Entrance: NEC Article 230 provides guidelines on service entrance conductors, including their installation, insulation, and protection. It specifies requirements for the size and rating of the service entrance conductors and the means to connect to the utility supply.
  • Overcurrent Protection: NEC requires that every service have appropriate overcurrent protection (such as circuit breakers or fuses) to protect against excess current which can cause fire or equipment damage. For a 100 amp service, this typically means using a 100 amp breaker. The specific requirements for overcurrent protection devices are detailed in NEC Article 240.
  • Equipment Grounding: NEC Article 250 covers grounding and bonding requirements. It specifies how the grounding electrode system should be installed. This includes the use of grounding electrodes, grounding electrode conductors, and bonding of metallic parts to ensure a clear path to earth in case of a fault.
  • Conduit and Cable Protection: Articles like NEC 342, 344, and 358 cover the requirements for conduit systems such as Intermediate Metal Conduit (IMC), Rigid Metal Conduit (RMC), and Electrical Metallic Tubing (EMT), respectively. The choice of conduit type, size, and installation practices are all dictated by these articles, based on the type and size of the wires being protected.
  • Load Calculations: NEC Article 220 provides detailed instructions on how to calculate the load of a service or feeder, which is critical in determining if a 100 amp service is adequate for a specific application or if a higher capacity may be necessary based on the actual electrical load.

For a detailed and accurate application of these codes, referencing the latest edition of the NEC book is recommended, as codes can change with each new edition (updated every three years). For practical application and compliance, it is also advisable to consult or hire a licensed electrician familiar with local amendments to the NEC.