Landscape Lighting Tips and Garden Lights Low Voltage
W. P. Law, Inc. has developed an in-depth low voltage lighting installation manual to provide you with a precise step-by-step method of designing and installing low voltage landscape lighting. Below is an excerpt from that manual. The complete manual is available in PDF format by clicking on the link below. A low voltage lighting calculator is also available in Excel format for transformer load calculations. Please click on the link below to download this useful tool.
Download & Print the Lighting Technical Guide by Clicking here.Download the Lighting Calculator by clicking here.
Transformers
Transformer Locations
The next step involves the location of the transformers. First you’ll want to guesstimate how many transformers might be needed for the job. At this point simply add up all the wattages of all the fixtures used. It is sometimes easier to use more than one transformer in different locations. This will keep your wire runs to a minimum and allow for easier zoning of the lights. Zoning the transformers this way will allow you to run areas independently. This will save money in the operation of the system. If, for example, both the back yard and front yard including the side yards yield 800 total watts used, two transformers of some wattage will be needed. [The calculations for the absolute wattage required for the transformers will be shown shortly.] Designate an area for each transformer, preferably as close to the center of each system as possible.
Setting up the Hubs
In the past, when low voltage tungsten bulbs were used, the fixtures where daisy- chained* with no real attention paid to bulb brightness, color or longevity because tungsten bulbs can burn for years on very little voltage. The newer halogen bulbs on the other hand, produce a white light giving a truer color but operate in a narrower voltage range of 10.8 to 12 volts. Therefore, to help the bulbs last for their full life rating, the fixtures are arranged in a “spider” or “hub”** configuration. The fixtures used come from the factory with 25’ leads instead of the 18” leads in the past. The fixtures are arranged so that the leads can be tied together to a trunk wire leading back to the transformer. This trunk wire is referred to as a “homerun wire”. How many lights tied together at a hub will depend on the total wattage of the hub. A rule-of-thumb is a maximum of 4-5, 20 or 35 watt fixtures per hub.
Of course some fixtures use smaller bulbs of 10 watts or less, so more of these lights may be tied together. Sometimes the full 25 foot lead is not used. If this occurs bury the extra at the base of the fixture or when using well low voltage garden lights, wrap the extra lead around the fixture. Never cut the leads to shorten them. The reason is that the voltage drop in the lead has been accounted for and cutting the leads will result in differing voltages for each fixture. The voltage reading at the hub must reflect the same reading for all lights in the group.
Controlling the Lights
The lighting transformer may be turned on or off by wiring it into a separate circuit using a wall switch or the lighting may be controlled remotely by attaching a timer, photocell or both to the transformer. The timer used may be either analog or digital. For simple lighting projects where the operation time is not varied during the week an analog timer is all that is required. This is a motorized timer with pins that can be placed around a dial to turn on or shut down the lighting at a prescribed time. This timer is limited to two start times per day. It also features a manual override on/off switch.
A digital timer may be used for more complex lighting systems where multiple start times are required including start times on different days of the week. The digital timer has an LCD display and is programmable using push buttons. This device has a battery back-up to preserve the memory in case of a power outage and also features a manual start cycle. Both timers fit a 120 volt outlet located on the face of the transformer. To install a timer simply remove the plug from the outlet, insert the timer into the outlet, then re-plug the transformer into the outlet on the side of the timer.
A photocell can be used in lieu of the timers and will operate the transformer from dusk to dawn. In order to conserve power, it is recommended to use the photo cell in conjunction with a timer to turn the power off at a predetermined time in the evening. Another advantage to using a timer/photocell combination is to avoid having to reset the timer when the yearly time changes occur.
The photocell is attached to the side of the transformer through a knock-out on its side. The photocell leads are passed through the chassis of the transformer and plugged in where the wire loop is connected. If the photocell is used, unplug the wire loop but do not discard it. This loop is used in conjunction with an amp meter to check the amp draw on the primary (120 volt) side of the transformer, when trouble-shooting the system. The photocell must receive direct sunlight in order to function properly. Avoid placing the transformer in an area that will become shaded as the sun changes positions. Because locations for transformer placement does not always provide for full sunlight, a photocell with a 25’ lead is available.
The Hub Connector
In the past, fixtures were attached at different locations along the main wire path using clunky two- piece wire piercing connectors or the line was cut and specialty gel filled wire nuts were used to make the splice. The problem is that in order for low voltage cable to be flexible it is composed of stranded wire and with every connection made, some voltage loss occurs because a secure connection could not be obtained every time. The hub makes use of a brass set screw wire connector that will hold 4-5 wire leads plus the homerun wire securely. In addition, a protective cap filled with a dielectric compound is screwed over the connector to protect the wire from corrosion. The splice is then housed in an in ground junction box to facilitate ease of maintenance and location of the hub.
