What is used by most installers to power transformers and sirens?

• A. 18/2
• B. 16/3
• C. 14/2
• D. 22/4

Answer: (A)

The choice hinges on matching a practical low-voltage power run to the current you need while keeping installation simple and cost-effective. For powering transformers and sirens, a two-conductor cable in 18-gauge is the standard. It provides enough current for typical low-voltage loads without being bulky or hard to pull through walls. It also keeps costs down and works well for the short to moderate runs common in alarm installations, with voltage drop remaining acceptable for these devices.

Using a thicker two-conductor like 14/2 isn’t usually necessary here; it’s more common for higher-current 120V circuits, and it adds stiffness and cost. A three-conductor option such as 16/3 isn’t needed unless you’re carrying an extra circuit or signaling line. A thinner option like 22 gauge (even in a multi-conductor 22/4) wouldn’t be reliable for power to a transformer or siren over typical distances because of greater voltage drop and heat risk, and it’s generally used only for low-current signaling rather than power.