########################################################################
# owuitools prompt test result
# prompt dir : medium/m03-dc-wire-gauge (round v3)
# chat id    : 202f0330-2330-4aaf-ad70-d6c69010c518
# chat title : Copper Wire Gauge for 12V 20A Load
# user       : the operator
# model      : qwen3.8:latest
# turns      : 2 messages on selected branch
# tool calls : 7  wiring_calc x7
# dumped at  : 2026-09-11T23:21:57Z
########################################################################

=== USER  (2026-09-11T23:20:11Z) ===
I need to run 12 V DC to a 20 A load that's 30 feet from the battery. What copper wire gauge keeps the voltage drop under 3%? Show the actual drop for the gauge you pick and for the next size smaller, so I can see the margin.

=== ASSISTANT  (2026-09-11T23:20:11Z, model qwen3.8:latest) ===
usage: prompt_eval_count=14977 eval_count=938 prompt_tokens=14977 completion_tokens=938 total=28.2s prefill=2.4s decode=25.7s 36.6 tok/s

=== [1] THINKING (27s) ===
The user wants a wire gauge calculation for 12V DC, 20A load, 30 feet. Voltage drop < 3%.

Let me think about this. The run is 30 feet one way, so total circuit length is 60 feet (round trip).

Voltage drop formula: V_drop = 2 × L × I × R_per_foot (where R is resistance per foot of wire, L is one-way length).

Actually, V_drop = I × R_total where R_total = 2 × L × R_per_foot.

3% of 12V = 0.36V max drop.

Let me use the wiring_calc tool for voltage drop. It takes AWG, length, current, voltage.

Let me check AWG properties and voltage drop. Let me calculate for a few gauges.

Let me think about what gauge would work. For 20A over 60 feet total, we need low resistance.

Let me compute. Resistance per foot (copper):
- 10 AWG: ~1.0 ohm/1000 ft = 0.001 ohm/ft
- 8 AWG: ~0.647 ohm/1000 ft = 0.000647 ohm/ft
- 6 AWG: ~0.407 ohm/1000 ft

For 30 ft one way, round trip 60 ft.

Using 10 AWG: R_total = 60 ft × 0.001 ohm/ft = 0.06 ohm. V_drop = 20A × 0.06 = 1.2V. That's 10% of 12V. Too much.

8 AWG: R_total = 60 × 0.000647 = 0.0388 ohm. V_drop = 20 × 0.0388 = 0.776V. That's 6.5%. Still over 3%.

6 AWG: R_total = 60 × 0.000407 = 0.0244 ohm. V_drop = 20 × 0.0244 = 0.488V. That's 4.07%. Still over 3%!

4 AWG: ~0.253 ohm/1000 ft = 0.000253 ohm/ft. R_total = 60 × 0.000253 = 0.0152 ohm. V_drop = 20 × 0.0152 = 0.304V. That's 2.53%. Under 3%!

So 4 AWG works, 6 AWG does not.

Wait, let me double check the resistance values. These are from memory - I should use the tool. Let me use wiring_calc with awg_properties and voltage_drop.

Actually the question asks to show the actual drop for the gauge I pick AND the next size smaller. So if I pick 4 AWG, show 4 AWG and 6 AWG.

Let me verify with the tools. Let me run awg_properties for 4, 6, 8, 10 and voltage_drop calculations.

Note: the user says "30 feet from the battery" - I'll assume that's one-way distance, so round trip is 60 ft. I should state this assumption clearly.

Let me use the tools. I'll do voltage_drop for 4, 6, 8, 10 AWG with length 30 (one-way? or total?).

Hmm, the voltage_drop tool - I need to check whether it takes one-way or round-trip length. Let me look. The description says "One-way cable length in metres." for length. Wait, it says metres but the user is in feet. Let me check - the tool uses SI (metres). But the user gave feet. Let me convert: 30 ft = 9.144 m.

Actually wait, let me re-read: "length": "One-way cable length in metres." So it takes one-way length in metres and presumably computes round-trip internally. Let me verify by running it.

Let me just run the tools and see what they return. Let me do awg_properties first to get resistance, and voltage_drop.

Actually, let me be careful. Let me run several in parallel:
- awg_properties for 4, 6, 8, 10
- voltage_drop for each with length 9.144 m (30 ft one way), current 20A, voltage 12V

Let me batch these.

Actually, let me reconsider whether the tool does round-trip automatically. I'll run one and check the output, then decide. But to save time, let me run them all and read the outputs carefully.

Let me run awg_properties for 4, 6, 8, 10 in parallel first.

=== [2] ASSISTANT TEXT ===
I'll work this out properly. First, a key assumption: "30 feet from the battery" I'm reading as **one-way** distance, so the current travels 60 ft of wire total (out and back) — that's what sets the drop. Let me pull the real resistance figures and compute drops rather than guess.

=== [3] TOOL CALL: wiring_calc  (call_9glenm5e) ===
{
  "calculation": "awg_properties",
  "awg": 4
}

=== [4] TOOL CALL: wiring_calc  (call_fzbsrz57) ===
{
  "calculation": "awg_properties",
  "awg": 6
}

=== [5] TOOL CALL: wiring_calc  (call_onbq2r8i) ===
{
  "calculation": "awg_properties",
  "awg": 8
}

=== [6] TOOL CALL: wiring_calc  (call_3ptx8avw) ===
{
  "calculation": "awg_properties",
  "awg": 10
}

=== [7] TOOL RESULT: wiring_calc  (call_9glenm5e) ===
# 4 AWG

Diameter:            5.189 mm (204.3 mil)
Cross-section:       21.1506 mm²
Resistance (copper): 0.815 Ω/km  (0.00025 Ω/ft)

Current rating, chassis/free-air wiring: 135 A
Current rating, power transmission:      60 A

The two figures differ because power transmission assumes bundled cable in a conduit where heat cannot escape, so it is far more conservative.

NEC Table 310.16 allowable ampacity (<=3 current-carrying conductors, 30 C ambient):
                60 C     75 C     90 C
  copper         70 A     85 A     95 A
  aluminium      80 A    100 A    115 A
Use the column matching the **termination** rating, not the insulation: NEC 110.14(C) limits most equipment to the 75 C column even with 90 C wire such as THHN. Quote the column you used - reading 60 C values under a 75 C heading is the usual mistake here.
These are 30 C ambient with no bundling. Correct for ambient (310.15(B)(1)) and for more than three conductors (310.15(C)(1)) before using them.

AC values from NEC Ch.9 Table 9 (75 °C, 60 Hz, 3 single conductors in conduit):
  PVC/aluminium conduit: R 1.020 Ω/km, X 0.157 Ω/km
  steel conduit:         R 1.020 Ω/km, X 0.197 Ω/km

**Do not work the AC drop out by hand from these.** Call this tool again with calculation=three_phase_drop (awg, length, current, voltage, power_factor, conduit) and it returns the drop, the percentage and the voltage at the load.
Hand-worked three-phase drops are wrong more often than they are right: the √3 factor gets written into the formula and then left out of the multiplication, which understates the answer by 1.73x and turns a marginal feeder into a passing one.


**For mains or building wiring, follow your local electrical code (NEC 310.16 in the US, BS 7671 in the UK) rather than these figures.** They are free-air rules of thumb; real installations derate for bundling, insulation rating, ambient temperature and conduit fill.

=== [8] TOOL RESULT: wiring_calc  (call_fzbsrz57) ===
# 6 AWG

Diameter:            4.115 mm (162.0 mil)
Cross-section:       13.3018 mm²
Resistance (copper): 1.296 Ω/km  (0.00040 Ω/ft)

Current rating, chassis/free-air wiring: 101 A
Current rating, power transmission:      37 A

The two figures differ because power transmission assumes bundled cable in a conduit where heat cannot escape, so it is far more conservative.

NEC Table 310.16 allowable ampacity (<=3 current-carrying conductors, 30 C ambient):
                60 C     75 C     90 C
  copper         55 A     65 A     75 A
  aluminium      60 A     75 A     85 A
Use the column matching the **termination** rating, not the insulation: NEC 110.14(C) limits most equipment to the 75 C column even with 90 C wire such as THHN. Quote the column you used - reading 60 C values under a 75 C heading is the usual mistake here.
These are 30 C ambient with no bundling. Correct for ambient (310.15(B)(1)) and for more than three conductors (310.15(C)(1)) before using them.

AC values from NEC Ch.9 Table 9 (75 °C, 60 Hz, 3 single conductors in conduit):
  PVC/aluminium conduit: R 1.610 Ω/km, X 0.167 Ω/km
  steel conduit:         R 1.610 Ω/km, X 0.210 Ω/km

**Do not work the AC drop out by hand from these.** Call this tool again with calculation=three_phase_drop (awg, length, current, voltage, power_factor, conduit) and it returns the drop, the percentage and the voltage at the load.
Hand-worked three-phase drops are wrong more often than they are right: the √3 factor gets written into the formula and then left out of the multiplication, which understates the answer by 1.73x and turns a marginal feeder into a passing one.


**For mains or building wiring, follow your local electrical code (NEC 310.16 in the US, BS 7671 in the UK) rather than these figures.** They are free-air rules of thumb; real installations derate for bundling, insulation rating, ambient temperature and conduit fill.

=== [9] TOOL RESULT: wiring_calc  (call_onbq2r8i) ===
# 8 AWG

Diameter:            3.264 mm (128.5 mil)
Cross-section:       8.3656 mm²
Resistance (copper): 2.061 Ω/km  (0.00063 Ω/ft)

Current rating, chassis/free-air wiring: 73 A
Current rating, power transmission:      24 A

The two figures differ because power transmission assumes bundled cable in a conduit where heat cannot escape, so it is far more conservative.

NEC Table 310.16 allowable ampacity (<=3 current-carrying conductors, 30 C ambient):
                60 C     75 C     90 C
  copper         40 A     50 A     55 A
  aluminium      45 A     55 A     60 A
Use the column matching the **termination** rating, not the insulation: NEC 110.14(C) limits most equipment to the 75 C column even with 90 C wire such as THHN. Quote the column you used - reading 60 C values under a 75 C heading is the usual mistake here.
These are 30 C ambient with no bundling. Correct for ambient (310.15(B)(1)) and for more than three conductors (310.15(C)(1)) before using them.

AC values from NEC Ch.9 Table 9 (75 °C, 60 Hz, 3 single conductors in conduit):
  PVC/aluminium conduit: R 2.560 Ω/km, X 0.171 Ω/km
  steel conduit:         R 2.560 Ω/km, X 0.213 Ω/km

**Do not work the AC drop out by hand from these.** Call this tool again with calculation=three_phase_drop (awg, length, current, voltage, power_factor, conduit) and it returns the drop, the percentage and the voltage at the load.
Hand-worked three-phase drops are wrong more often than they are right: the √3 factor gets written into the formula and then left out of the multiplication, which understates the answer by 1.73x and turns a marginal feeder into a passing one.


**For mains or building wiring, follow your local electrical code (NEC 310.16 in the US, BS 7671 in the UK) rather than these figures.** They are free-air rules of thumb; real installations derate for bundling, insulation rating, ambient temperature and conduit fill.

=== [10] TOOL RESULT: wiring_calc  (call_3ptx8avw) ===
# 10 AWG

Diameter:            2.588 mm (101.9 mil)
Cross-section:       5.2612 mm²
Resistance (copper): 3.277 Ω/km  (0.00100 Ω/ft)

Current rating, chassis/free-air wiring: 55 A
Current rating, power transmission:      15 A

The two figures differ because power transmission assumes bundled cable in a conduit where heat cannot escape, so it is far more conservative.

NEC Table 310.16 allowable ampacity (<=3 current-carrying conductors, 30 C ambient):
                60 C     75 C     90 C
  copper         30 A     35 A     40 A
  aluminium      35 A     40 A     45 A
Use the column matching the **termination** rating, not the insulation: NEC 110.14(C) limits most equipment to the 75 C column even with 90 C wire such as THHN. Quote the column you used - reading 60 C values under a 75 C heading is the usual mistake here.
NEC 240.4(D) also caps overcurrent protection for 10 AWG at 30 A regardless of the ampacity above.
These are 30 C ambient with no bundling. Correct for ambient (310.15(B)(1)) and for more than three conductors (310.15(C)(1)) before using them.

AC values from NEC Ch.9 Table 9 (75 °C, 60 Hz, 3 single conductors in conduit):
  PVC/aluminium conduit: R 3.900 Ω/km, X 0.164 Ω/km
  steel conduit:         R 3.900 Ω/km, X 0.207 Ω/km

**Do not work the AC drop out by hand from these.** Call this tool again with calculation=three_phase_drop (awg, length, current, voltage, power_factor, conduit) and it returns the drop, the percentage and the voltage at the load.
Hand-worked three-phase drops are wrong more often than they are right: the √3 factor gets written into the formula and then left out of the multiplication, which understates the answer by 1.73x and turns a marginal feeder into a passing one.


**For mains or building wiring, follow your local electrical code (NEC 310.16 in the US, BS 7671 in the UK) rather than these figures.** They are free-air rules of thumb; real installations derate for bundling, insulation rating, ambient temperature and conduit fill.

=== [11] THINKING ===
Now I have resistance per foot:
- 4 AWG: 0.00025 Ω/ft
- 6 AWG: 0.00040 Ω/ft
- 8 AWG: 0.00063 Ω/ft
- 10 AWG: 0.00100 Ω/ft

Now let me compute the DC voltage drop. The user is on DC, so I use the voltage_drop calculation (DC). Let me run voltage_drop for 4, 6, 8, 10 with length (one-way) = 9.144 m (30 ft), current 20A, voltage 12V.

Wait, but I need to check whether the tool interprets length as one-way and doubles it, or expects total. The description says "One-way cable length in metres." So it should double internally. Let me run and verify.

Let me run voltage_drop for 4, 6, 8, 10.

=== [12] TOOL CALL: wiring_calc  (call_h51jldd7) ===
{
  "awg": 4,
  "calculation": "voltage_drop",
  "current": "20",
  "length": "9.144",
  "voltage": "12"
}

=== [13] TOOL CALL: wiring_calc  (call_702gbikj) ===
{
  "awg": 6,
  "calculation": "voltage_drop",
  "current": "20",
  "length": "9.144",
  "voltage": "12"
}

=== [14] TOOL CALL: wiring_calc  (call_4g9t0saf) ===
{
  "awg": 8,
  "calculation": "voltage_drop",
  "current": "20",
  "length": "9.144",
  "voltage": "12"
}

=== [15] TOOL RESULT: wiring_calc  (call_h51jldd7) ===
# Voltage drop over 9.144 m of 4 AWG

**Drop: 298.1 mV**  (round trip, 18.288 m of conductor)

Conductor: 4 AWG = 21.15 mm² (5.19 mm diameter), 0.815 Ω/km
Loop resistance: 14.91 mΩ
Power lost as heat: 5.963 W

That is 2.48% of a 12 V supply — within the usual 3% guideline.
Voltage at the load: 11.7 V

## Nearby gauges, same run

-   1 AWG ( 42.41 mm²): 148.7 mV = 1.24%
-   2 AWG ( 33.63 mm²): 187.5 mV = 1.56%
-   3 AWG ( 26.67 mm²): 236.4 mV = 1.97%
-   5 AWG ( 16.77 mm²): 375.9 mV = 3.13%
-   6 AWG ( 13.30 mm²): 474 mV = 3.95%
-   7 AWG ( 10.55 mm²): 597.8 mV = 4.98%

Lower AWG numbers mean thicker wire and less drop.


**For mains or building wiring, follow your local electrical code (NEC 310.16 in the US, BS 7671 in the UK) rather than these figures.** They are free-air rules of thumb; real installations derate for bundling, insulation rating, ambient temperature and conduit fill.

=== [16] TOOL RESULT: wiring_calc  (call_702gbikj) ===
# Voltage drop over 9.144 m of 6 AWG

**Drop: 474 mV**  (round trip, 18.288 m of conductor)

Conductor: 6 AWG = 13.30 mm² (4.12 mm diameter), 1.296 Ω/km
Loop resistance: 23.7 mΩ
Power lost as heat: 9.481 W

That is 3.95% of a 12 V supply — above the usual 3% guideline — consider thicker wire or a shorter run.
Voltage at the load: 11.53 V

## Nearby gauges, same run

-   3 AWG ( 26.67 mm²): 236.4 mV = 1.97%
-   4 AWG ( 21.15 mm²): 298.1 mV = 2.48%
-   5 AWG ( 16.77 mm²): 375.9 mV = 3.13%
-   7 AWG ( 10.55 mm²): 597.8 mV = 4.98%
-   8 AWG (  8.37 mm²): 753.8 mV = 6.28%
-   9 AWG (  6.63 mm²): 950.5 mV = 7.92%

Lower AWG numbers mean thicker wire and less drop.


**For mains or building wiring, follow your local electrical code (NEC 310.16 in the US, BS 7671 in the UK) rather than these figures.** They are free-air rules of thumb; real installations derate for bundling, insulation rating, ambient temperature and conduit fill.

=== [17] TOOL RESULT: wiring_calc  (call_4g9t0saf) ===
# Voltage drop over 9.144 m of 8 AWG

**Drop: 753.8 mV**  (round trip, 18.288 m of conductor)

Conductor: 8 AWG = 8.37 mm² (3.26 mm diameter), 2.061 Ω/km
Loop resistance: 37.69 mΩ
Power lost as heat: 15.08 W

That is 6.28% of a 12 V supply — above the usual 3% guideline — consider thicker wire or a shorter run.
Voltage at the load: 11.25 V

## Nearby gauges, same run

-   5 AWG ( 16.77 mm²): 375.9 mV = 3.13%
-   6 AWG ( 13.30 mm²): 474 mV = 3.95%
-   7 AWG ( 10.55 mm²): 597.8 mV = 4.98%
-   9 AWG (  6.63 mm²): 950.5 mV = 7.92%
-  10 AWG (  5.26 mm²): 1.199 V = 9.99%
-  11 AWG (  4.17 mm²): 1.511 V = 12.59%

Lower AWG numbers mean thicker wire and less drop.


**For mains or building wiring, follow your local electrical code (NEC 310.16 in the US, BS 7671 in the UK) rather than these figures.** They are free-air rules of thumb; real installations derate for bundling, insulation rating, ambient temperature and conduit fill.

=== [18] THINKING (8s) ===
The tool confirms my hand calculation:
- 4 AWG: 298.1 mV = 2.48% ✓ under 3%
- 6 AWG: 474 mV = 3.95% ✗ over 3%
- 8 AWG: 753.8 mV = 6.28% ✗

So the answer is 4 AWG (which passes at 2.48%), and the next size smaller (6 AWG) fails at 3.95%.

Note: 5 AWG would be 3.13%, also over 3%. So 4 AWG is the smallest standard gauge that passes. Good.

The tool's voltage_drop uses round trip automatically (it doubled the length to 18.288 m). 

Now let me write a clear answer. I'll state the assumption (30 ft one-way, so 60 ft round trip), give the pick (4 AWG), show its drop (298 mV, 2.48%, load sees 11.70V), and the next smaller (6 AWG, 474 mV, 3.95%, load sees 11.53V). Also note 5 AWG at 3.13% also fails. Mention ampacity is fine (20A well within all these). Note heat loss.

Let me present this cleanly.

=== [19] ASSISTANT TEXT ===
**Pick: 4 AWG copper.** At 30 ft one‑way (60 ft / 18.29 m round trip) it drops **298 mV = 2.48%** — under your 3% limit, with the load seeing about **11.70 V**.

Here's the margin you asked for:

| Gauge | Round‑trip loop R | Drop @ 20 A | % of 12 V | Load sees | Pass? |
|-------|------------------|-------------|-----------|-----------|-------|
| **4 AWG** (chosen) | 14.9 mΩ | **298 mV** | **2.48%** | 11.70 V | ✅ |
| **6 AWG** (next smaller) | 23.7 mΩ | **474 mV** | **3.95%** | 11.53 V | ❌ |

So the step down from 4 to 6 AWG costs you ~1.5× the drop and pushes you over the line. (For completeness, 5 AWG lands at 376 mV / 3.13% — also a fail, so 4 AWG is the smallest standard size that clears 3%. 8 AWG would be 754 mV / 6.28%.)

A few things worth knowing before you buy wire:

- **The math assumes 30 ft one way.** If "30 feet" was meant as the total round‑trip length, then 6 AWG would actually clear it (~1.98%) — but I've sized it for the worst case.
- **Ampacity is not your constraint here.** 20 A is well inside every gauge's rating (even 10 AWG is rated 30 A), so this is purely a voltage‑drop decision.
- **Heat in the wire:** 4 AWG dissipates ~6 W, 6 AWG ~9.5 W over the run. Not dangerous, but it's why the load voltage sags.
- **Battery sag under load:** a real 12 V battery isn't exactly 12.0 V under 20 A of load — if the system is marginal (e.g., starting an engine or running a compressor), consider 2 AWG (~1.56%) for extra headroom, since the drop scales linearly with current and any momentary surge will eat into your margin.
- These are free‑air copper figures; derate if the cable runs hot, bundled, or through conduit for long stretches.

Rule of thumb if you want to check other loads yourself: **Drop ≈ 2 × L(ft) × I(A) × R(Ω/ft)**, where the factor of 2 accounts for the return path.

=== STATUS HISTORY (live progress indicator) ===
- Processing prompt
- Thinking · first token after 6.2 s
- Thought: The user wants a wire gauge calculation for 12V DC, 20A load, 30 feet. Voltage drop < … Let me run awg_properties for 4, 6, 8, 10 in parallel first.
- Writing response
- Calling wiring_calc
- Calling wiring_calc
- Calling wiring_calc
- Calling wiring_calc
- Thinking
- Thought: Now I have resistance per foot: - 4 AWG: 0.00025 Ω/ft - 6 AWG: 0.00040 Ω/ft - 8 AWG: … Let me run and verify. Let me run voltage_drop for 4, 6, 8, 10.
- Calling wiring_calc
- Calling wiring_calc
- Calling wiring_calc
- Thinking
- Thought: The tool confirms my hand calculation: - 4 AWG: 298.1 mV = 2.48% ✓ under 3% - 6 AWG: … within all these). Note heat loss. Let me present this cleanly.
- Writing response
- Done · 7 tool calls · prefill 6.0 s for 12,871 tokens · 2,781 generated
