Products, Vendors, CAD Files, Spec Sheets and More...
Sign up for LAWeekly newsletter
From the outside, landscape lighting transformers seem rather uninteresting. They are boxes with plugs and they all do pretty much the same thing ?EUR??,,????'?????< Why then, are there so many transformers on the market that vary considerably in price and features? The following questions and answers should shed some light on what?EUR??,,????'?????< Why should I care about the transformer core? It?EUR??,,????'?????< There are two main core configurations used in landscape lighting transformers, the laminated type (EI) and toroidal. The toroidal core has several advantages over the EI Laminated type. 1. Higher efficiency (approx. 95% vs. 85%)?EUR??,,????'?????< 2. Runs cooler?EUR??,,????'?????< 3. Runs quieter, vibrates less?EUR??,,????'?????< How do I know if the core is toroidal or EI laminated? The manufacturer?EUR??,,????'?????< I?EUR??,,????'?????< Barbeques and meltdowns can occur in a transformer for two reasons. Here?EUR??,,????'?????< 1. Don?EUR??,,????'?????< While secondary breakers or fuses are meant to protect from overloading, they do so only for the secondary common taps. Voltage taps can also be overloaded on some transformers. For example, one manufacturer warns to load no more than 600 watts on a single voltage tap (for their 1,120 watt transformer!) This precaution could easily be missed. Better transformers accept the full transformer load on any single voltage tap. Also important is temperature rating of internal wiring. Many transformers use 105 degree C wire while better manufacturers specify 150 degrees C for their wiring. 2. Tighten terminal block set screws. Internal transformer wires terminate at the common and voltage terminals. These wires are secured by setscrews that can become loose in time. Such loose connections can lead to arcing in the terminal block creating enough heat to melt internal wiring. All setscrews should be tightened upon installation and once a year thereafter. What protects the homeowner, the house, the dog and me from shocking, burning or exploding transformers? First, all the major manufacturers of professional-quality landscape lighting transformers produce units possessing a high degree of safety. Accidents are extremely rare. This level of safety can be compromised, however, by an inexperienced or poorly trained installer. Also, the built-in protective devices vary in how foolproof they are. There are three types of protective devices in UL-listed transformers. (For non-UL-listed users, you?EUR??,,????'?????< 1. Thermal breakers. These heat-activated breakers are tripped when temperatures exceed a maximum then automatically reset when cool. Thermal breakers, a UL requirement, are inaccessible to the user (usually built into the core assembly) and are triggered in only the most severe meltdowns. 2. Fuses. Some manufacturers use standard fuses to protect the primary and/or secondary circuits. Fuses are problematic because they require replacement when blown and they can be replaced with fuses of the wrong rating. They can also be bypassed entirely by an imaginative homeowner possessing a paper clip or gum wrapper! 3. Magnetic circuit breakers. These are the best over-current protectors since they can be reset. They can also be used to temporarily switch circuits on and off. Time clocks and photocells mounted on the transformer are used to turn on the transformer at dusk then off at a predetermined time. To improve access during installation, the transformer wiring can be done with the unit lying on a box or on the ground. Why do some transformers have an extra common tap? UL listings and NEC codes limit the size of a secondary transformer circuit to 300 Watts (25 Amps). For this reason, most manufacturers assign one common tap for each 300 Watts of total capacity ?EUR??,,????'?????< Why do manufacturers and contractors agree to disagree on UL 1838? In 1994, Underwriter Laboratories (UL) set a new standard for Low Voltage Landscape Lighting Systems (UL 1838). This standard specifies the mechanical and electrical configuration of all system components (transformers, wire and fixtures) and minimum performance standards for each component. This listing limits landscape lighting transformer voltage to 15 volts. Since UL is so well respected, many contractors insist on only purchasing transformers listed under 1838. Manufacturers, on the other hand, responding to the contractors?EUR??,,????'?????< A little history: Since UL?EUR??,,????'?????< Testing for electrical shock potential is more difficult. (It would be hard to find volunteers.) Instead, UL relied upon published literature on the effects of electric current on humans. The basis of their conclusions comes from a 1961 study by a Berkeley Professor, C. F. Dalziel. Professor Dalziel subjected his unfortunate students to electric shocks, recorded their reactions and presented his findings to the International Electrotechnical Commission (IEC) in Switzerland. While the professor was unable to shock his students to death, he was willing to guess at what current such demise would require; his guess approximated 21 volts under a worst-case contact scenario. This is why UL 1838 (being on the safe-side) limits transformer voltage to 15 Volts. Coming back to the present, the IEC who continued studying the subject completed a more comprehensive investigation. With a greater degree of certainty, they concluded that there is a negligible risk of death from any current less than 30 Milliamps. In a worst-case installation scenario, this corresponds to 30 Volts. Their findings are further strengthened by the fact that there have been no recorded deaths (ever) from contact with any current less than 30 volts. In fact, death from any current below 120 volts is extremely rare. With this new data in hand, UL is rumored to be amending UL 1838 with a higher voltage limit. In fact, they are in a final draft of UL 2108, a new standard that applies to indoor low voltage lighting systems. The new voltage maximum? 30 Volts.
Why then, are there so many transformers on the market that vary considerably in price and features? The following questions and answers should shed some light on what?EUR??,,????'?????<
It?EUR??,,????'?????< There are two main core configurations used in landscape lighting transformers, the laminated type (EI) and toroidal. The toroidal core has several advantages over the EI Laminated type. 1. Higher efficiency (approx. 95% vs. 85%)?EUR??,,????'?????< 2. Runs cooler?EUR??,,????'?????< 3. Runs quieter, vibrates less?EUR??,,????'?????< How do I know if the core is toroidal or EI laminated? The manufacturer?EUR??,,????'?????< I?EUR??,,????'?????< Barbeques and meltdowns can occur in a transformer for two reasons. Here?EUR??,,????'?????< 1. Don?EUR??,,????'?????< While secondary breakers or fuses are meant to protect from overloading, they do so only for the secondary common taps. Voltage taps can also be overloaded on some transformers. For example, one manufacturer warns to load no more than 600 watts on a single voltage tap (for their 1,120 watt transformer!) This precaution could easily be missed. Better transformers accept the full transformer load on any single voltage tap. Also important is temperature rating of internal wiring. Many transformers use 105 degree C wire while better manufacturers specify 150 degrees C for their wiring. 2. Tighten terminal block set screws. Internal transformer wires terminate at the common and voltage terminals. These wires are secured by setscrews that can become loose in time. Such loose connections can lead to arcing in the terminal block creating enough heat to melt internal wiring. All setscrews should be tightened upon installation and once a year thereafter. What protects the homeowner, the house, the dog and me from shocking, burning or exploding transformers? First, all the major manufacturers of professional-quality landscape lighting transformers produce units possessing a high degree of safety. Accidents are extremely rare. This level of safety can be compromised, however, by an inexperienced or poorly trained installer. Also, the built-in protective devices vary in how foolproof they are. There are three types of protective devices in UL-listed transformers. (For non-UL-listed users, you?EUR??,,????'?????< 1. Thermal breakers. These heat-activated breakers are tripped when temperatures exceed a maximum then automatically reset when cool. Thermal breakers, a UL requirement, are inaccessible to the user (usually built into the core assembly) and are triggered in only the most severe meltdowns. 2. Fuses. Some manufacturers use standard fuses to protect the primary and/or secondary circuits. Fuses are problematic because they require replacement when blown and they can be replaced with fuses of the wrong rating. They can also be bypassed entirely by an imaginative homeowner possessing a paper clip or gum wrapper! 3. Magnetic circuit breakers. These are the best over-current protectors since they can be reset. They can also be used to temporarily switch circuits on and off.
There are two main core configurations used in landscape lighting transformers, the laminated type (EI) and toroidal.
The toroidal core has several advantages over the EI Laminated type.
1. Higher efficiency (approx. 95% vs. 85%)?EUR??,,????'?????<
2. Runs cooler?EUR??,,????'?????<
3. Runs quieter, vibrates less?EUR??,,????'?????<
The manufacturer?EUR??,,????'?????<
Barbeques and meltdowns can occur in a transformer for two reasons. Here?EUR??,,????'?????< 1. Don?EUR??,,????'?????< While secondary breakers or fuses are meant to protect from overloading, they do so only for the secondary common taps. Voltage taps can also be overloaded on some transformers. For example, one manufacturer warns to load no more than 600 watts on a single voltage tap (for their 1,120 watt transformer!) This precaution could easily be missed. Better transformers accept the full transformer load on any single voltage tap. Also important is temperature rating of internal wiring. Many transformers use 105 degree C wire while better manufacturers specify 150 degrees C for their wiring. 2. Tighten terminal block set screws. Internal transformer wires terminate at the common and voltage terminals. These wires are secured by setscrews that can become loose in time. Such loose connections can lead to arcing in the terminal block creating enough heat to melt internal wiring. All setscrews should be tightened upon installation and once a year thereafter.
1. Don?EUR??,,????'?????< While secondary breakers or fuses are meant to protect from overloading, they do so only for the secondary common taps. Voltage taps can also be overloaded on some transformers. For example, one manufacturer warns to load no more than 600 watts on a single voltage tap (for their 1,120 watt transformer!) This precaution could easily be missed. Better transformers accept the full transformer load on any single voltage tap. Also important is temperature rating of internal wiring. Many transformers use 105 degree C wire while better manufacturers specify 150 degrees C for their wiring.
2. Tighten terminal block set screws. Internal transformer wires terminate at the common and voltage terminals. These wires are secured by setscrews that can become loose in time. Such loose connections can lead to arcing in the terminal block creating enough heat to melt internal wiring. All setscrews should be tightened upon installation and once a year thereafter.
First, all the major manufacturers of professional-quality landscape lighting transformers produce units possessing a high degree of safety. Accidents are extremely rare. This level of safety can be compromised, however, by an inexperienced or poorly trained installer. Also, the built-in protective devices vary in how foolproof they are.
There are three types of protective devices in UL-listed transformers. (For non-UL-listed users, you?EUR??,,????'?????<
1. Thermal breakers. These heat-activated breakers are tripped when temperatures exceed a maximum then automatically reset when cool. Thermal breakers, a UL requirement, are inaccessible to the user (usually built into the core assembly) and are triggered in only the most severe meltdowns.
2. Fuses. Some manufacturers use standard fuses to protect the primary and/or secondary circuits. Fuses are problematic because they require replacement when blown and they can be replaced with fuses of the wrong rating. They can also be bypassed entirely by an imaginative homeowner possessing a paper clip or gum wrapper!
3. Magnetic circuit breakers. These are the best over-current protectors since they can be reset. They can also be used to temporarily switch circuits on and off.
UL listings and NEC codes limit the size of a secondary transformer circuit to 300 Watts (25 Amps). For this reason, most manufacturers assign one common tap for each 300 Watts of total capacity ?EUR??,,????'?????<
In 1994, Underwriter Laboratories (UL) set a new standard for Low Voltage Landscape Lighting Systems (UL 1838). This standard specifies the mechanical and electrical configuration of all system components (transformers, wire and fixtures) and minimum performance standards for each component.
This listing limits landscape lighting transformer voltage to 15 volts. Since UL is so well respected, many contractors insist on only purchasing transformers listed under 1838. Manufacturers, on the other hand, responding to the contractors?EUR??,,????'?????<
A little history: Since UL?EUR??,,????'?????<
Testing for electrical shock potential is more difficult. (It would be hard to find volunteers.) Instead, UL relied upon published literature on the effects of electric current on humans. The basis of their conclusions comes from a 1961 study by a Berkeley Professor, C. F. Dalziel.
Professor Dalziel subjected his unfortunate students to electric shocks, recorded their reactions and presented his findings to the International Electrotechnical Commission (IEC) in Switzerland. While the professor was unable to shock his students to death, he was willing to guess at what current such demise would require; his guess approximated 21 volts under a worst-case contact scenario. This is why UL 1838 (being on the safe-side) limits transformer voltage to 15 Volts.
Coming back to the present, the IEC who continued studying the subject completed a more comprehensive investigation. With a greater degree of certainty, they concluded that there is a negligible risk of death from any current less than 30 Milliamps. In a worst-case installation scenario, this corresponds to 30 Volts.
Their findings are further strengthened by the fact that there have been no recorded deaths (ever) from contact with any current less than 30 volts. In fact, death from any current below 120 volts is extremely rare.
With this new data in hand, UL is rumored to be amending UL 1838 with a higher voltage limit. In fact, they are in a final draft of UL 2108, a new standard that applies to indoor low voltage lighting systems. The new voltage maximum? 30 Volts.
Yes, aside from the safety concerns, using higher voltage taps wastes energy. Since energy consumption is a function of both voltage and resistance, shifting a wire run to the next higher voltage tap increases energy consumption by about 8 percent.
Rather than relying upon the higher voltages, installers can take steps to reduce the resistance on the wire run. They can do this in the following ways:
1. Using lower gauge wire.
2. Replacing one large transformer with two or smaller ones located closer to fixtures.
3. Using multiple wire runs instead of putting large lamp loads on single runs.
4. Reducing lamp wattage.
All these techniques reduce energy consumption. Of course there are times when the above methods are insufficient to keep the needed voltage to 15 Volts and higher taps are required. That?EUR??,,????'?????<
Source: CAST Lighting
12 to 22: Volts, the range commonly found of ?EUR??,,????'?????< 10.6 to 11.6: Volts, the optimum range, per fixture, of each light on a low voltage lighting system. 200: Percent, the lamp life gained from operating fixtures in a landscape lighting application at 11.6 volts. Source: Consumers Choice Lighting
10.6 to 11.6: Volts, the optimum range, per fixture, of each light on a low voltage lighting system.
200: Percent, the lamp life gained from operating fixtures in a landscape lighting application at 11.6 volts.
Francisco Uviña, University of New Mexico
Hardscape Oasis in Litchfield Park
Ash Nochian, Ph.D. Landscape Architect
November 12th, 2025
Sign up to receive Landscape Architect and Specifier News Magazine, LA Weekly and More...
Invalid Verification Code
Please enter the Verification Code below
You are now subcribed to LASN. You can also search and download CAD files and spec sheets from LADetails.