LED Lighting

In the case of LED lighting, it is generally not recommended to increase the wire size beyond what is specified by the manufacturer. Here's the reason: Power Efficiency

LED lights are highly efficient and draw very little current. Increasing the wire size would result in excess copper, which is not necessary and can actually reduce power efficiency.

Voltage Drop

Larger wire sizes have lower resistance, which means less voltage drop over the distance. However, with the low current draw of LED lights, the voltage drop is typically negligible, even with smaller wire sizes.

Cost

Using larger wire sizes increases the material cost without providing any significant benefits.

HVAC Split System Control Wiring

For HVAC split system control wiring, the following are possible reasons why using 12 gauge wire instead of 18 or 16 gauge could cause problems: Increased Resistance

12 gauge wire has a higher resistance compared to 18 or 16 gauge wire. This can lead to a voltage drop over the distance, which can affect the proper operation of control devices, such as thermostats and relays.

Overheating

Higher resistance can also cause the wire to generate more heat, which can be problematic in enclosed areas or near heat sources.

Code Requirements: Most local electrical codes specify the minimum wire size that must be used for HVAC control wiring. Using wire that is too small can violate code requirements and pose a safety hazard.In general, it is important to follow the manufacturer's recommendations and applicable electrical codes when wiring any electrical system. Using wire that is too large or too small can have unintended consequences. Flag for review