Choosing a Transformer
Image courtesy of Vista Professional Outdoor Lighting, www.vistapro.com
- Magnetic overload circuit breakers
Used for reliable automatic secondary circuit protection. Circuit breakers may also be used as on/off rocker switches. - 120-volt accessory receptacle
For use with optional, removable multisetting mechanical (TC-112) 24-hour timer or electronic/digital (DTC-150) 7-day timer (with battery backup). - Terminal strip
Used for multiple low voltage cable connections. Cover flap opens to color coded voltage taps. - Accessory terminal strip
For easy installation of optional photocell, motion sensor, or other external switching devices.
When planning a low-voltage lighting system for a client, consider these tips from the transformer engineers at Cast Lighting who give LCN their expertise on the features to look for in a high-quality transformer.
The single most important component of a low-voltage landscape lighting system is the multi-tap transformer. The design and construction of the transformer is critical to the proper functioning and safety of the system.
Select a Voltage Range Appropriate for the Job
The length of wire runs, the lamp load on each run and the wire type determine the extent of voltage loss. Halogen lamps used in the fixtures have a acceptable operating range of between 10.8 volts and 12.0 volts, with the optimal range of 11.0 to 11.5 volts.
Using calculations and direct voltage measurement at splice points, the correct voltage taps needed to deliver the optimum voltage to the lamp are determined. Most voltmeters are calibrated to have their greatest accuracy at 120 volts. At 12 volts, these meters may be more than one volt off. CAST Landscape Lighting offers a volt/amp meter specifically calibrated at 12 volts.
Since the final tap decisions are made in the field based on voltage measurements, you want to have the full range of voltages available.
Transformers have taps that range between 12 and 21 volts. Be sure to select the transformer that will accommodate your voltage needs.
Circuit Breakers
Overload protection is critical for any power supply. Transformer manufacturers use three main types of protection?EUR??,,????'???fuses, push-type breakers and magnetic breakers. Of the three, magnetic breakers are far superior in performance and functionality.
Fuses are troublesome in that they must be replaced when blown, they are subject to the user putting in the wrong fuse type and they can be bypassed entirely with a nail, foil or even a cigarette wrapper.
Push-type breakers perform well, but they cannot be used as a switch. Magnetic breakers are the best choice because of their durability, ease of use, and can be used to switch on or off individual common taps.
Look for transformers that offer circuit breakers on all secondary common taps. Some high-quality transformers include a breaker for the primary voltage as well. This added level of protection ensures that the entire transformer is protected, not just the secondary. A primary breaker also can function as an on/off switch for the transformer. Without that switch, the only way to turn off a transformer is at the main breaker box (may not be easily accessed) or at the external GFI outlet (this outlet is sealed when properly installed).
Homeowners often request that they be able to manually switch off certain lighting zones. Magnetic circuit breakers are ideal for this. The primary circuit breaker can be used as an on/off switch for the entire transformer.
Terminal Types
The best types of voltage and common (neutral) terminals are screw-type and can accommodate multiple wire runs. Some older transformer designs used wire runs that dangle from the core. The installer had to use wire nuts to make their connections. During the voltage adjustment phase of installation, wires need to be twisted in and out of wire nuts several times–each time the wire is damaged and must be re-stripped. Today, good transformer manufacturers use heavy-duty, screw-type terminals that allow multiple home-run wires to be screwed securely in place.
For a further exploration into the state-of-the-art of transformer technology, log onto the online resources at www.cast-lighting.com.
