G&D SMART / Professional outdoor lighting
18 AWG vs 20 AWG Wire for Permanent Outdoor Lighting
18 AWG VS 20 AWG PERMANENT OUTDOOR LIGHTING
18 AWG vs 20 AWG Wire for Permanent Outdoor Lighting
Wire gauge affects resistance, voltage drop, current margin, connector selection, cable size and total material cost. For professional permanent outdoor lighting, the correct choice depends on branch current, cable length, system voltage, connector limits and the exact wire construction—not AWG alone.
Quick Comparison
| Factor | 20 AWG | 18 AWG |
|---|---|---|
| Conductor size | Smaller | Larger |
| Resistance per unit length | Higher | Lower |
| Voltage drop at equal current and length | Higher | Lower |
| Current margin | Lower for the same construction | Higher for the same construction |
| Cable size / material cost | Usually lower | Usually higher |
| Typical G&D SMART use | Standard 24V UL2468 route in selected configurations | Higher-current / lower-drop 24V or 36V project route, depending on the exact cable |
Why 18 AWG Has Less Voltage Drop
A larger copper conductor has lower electrical resistance. At the same current and cable length, 18 AWG will normally lose less voltage than 20 AWG. That can help maintain more stable endpoint voltage and reduce connector and cable heating in demanding branches.
Voltage drop = Current × Total loop resistance. The total loop includes both the positive and negative conductor paths plus connector and contact resistance.
Planning Example: 24V, 4A Branch
Assume a 24V branch drawing 4A and a 20ft one-way extension, which creates approximately 40ft of copper loop length. Using typical copper resistance values near room temperature only as a planning example:
| Wire | Typical resistance basis* | Approx. loop drop at 4A | Approx. % of 24V |
|---|---|---|---|
| 20 AWG | ~10.2Ω / 1000ft | ~1.63V | ~6.8% |
| 18 AWG | ~6.4Ω / 1000ft | ~1.02V | ~4.3% |
*Illustrative copper-conductor values. Actual resistance changes with conductor construction, temperature, connectors and manufacturing tolerance. Measure the finished installation under load before setting an approved run length.
When 20 AWG Makes Sense
- The validated branch current and cable length fit the approved system design.
- Lower material cost and smaller cable size are important.
- The connector and finished cable assembly are already matched to the product.
- Voltage-drop testing confirms acceptable endpoint voltage under maximum intended load.
When 18 AWG Makes Sense
- The branch current is higher or the cable route is longer.
- More voltage-drop margin is required.
- The project uses a higher-current connector and cable assembly.
- The system is being designed around a professional 24V or 36V architecture that benefits from lower conductor resistance.
AWG Does Not Define Wet / Damp / Dry Rating
18 AWG is not automatically an outdoor Wet-location cable, and 20 AWG is not automatically indoor-only. AWG describes conductor size. The cable construction, insulation, listing/recognition, finished-product certification and installation environment determine where the cable can be used.
Compare SPT-2W vs UL2468 wire →
Connector Rating Can Become the Real Limit
Changing from 20 AWG to 18 AWG does not increase the current rating of an existing connector. The cable, connector, control-box output and fixture branch must all be checked together. A lower-resistance wire cannot compensate for an undersized connector or an overloaded output.
24V and 36V Use Cases
G&D SMART currently uses 24V as the core professional platform, with 20 AWG common in the standard UL2468 route and 18 AWG available when a lower-drop or different outdoor cable construction is required. For 36V projects, 18 AWG is the standard engineering direction in the current system architecture.
Frequently Asked Questions
Is 18 AWG always better than 20 AWG?
No. 18 AWG provides lower resistance, but it is larger and more expensive. If a validated 20 AWG design meets the required branch load, voltage drop, connector and installation conditions, increasing wire size may provide little practical benefit.
Can I replace 20 AWG with 18 AWG without changing anything else?
Not automatically. Confirm the connector crimp/contact range, cable outer diameter, sealing, strain relief, track routing and finished assembly before changing gauge.
Which wire is better for a 24V permanent lighting system?
For many standard 24V configurations, 20 AWG can be sufficient when branch current and run length are controlled. 18 AWG provides more voltage-drop margin for higher-current or longer-cable projects.
Does larger wire allow more lights on one branch?
Sometimes wire resistance is one limiting factor, but fixture load, connector current, control-box output, voltage drop, signal path and certification can limit the branch before the wire does.
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