CAST Voltage Calculator - Daisy Chain - T-Method - Spider Splice Method

 CAST Voltage Calculator - Daisy Chain - T-Method - Spider Splice Method
This excel worksheet is a low voltage LED system calculator that uses the daisy chain or T-Method wiring method.
Download the CAST Lighting LED System Calculator


  • File is in .xlsm format and may not open and/or function properly with old versions of excel
  • If download attempts are unsuccessful, then request calculator from CAST Lighting.

CAST Lighting has long been a proponent of the Spider Splice (Hub) Method of low voltage system wiring. With the introduction of low-wattage LED's, many contractors instead elect to use the old daisy chain method of wiring.

The daisy chain method involves running a home run wire from the transformer into the field - with fixtures spliced into this wire along its length. At some of these splice points, multiple fixtures may be connected together (combining the Spider Splice and Daisy Chain methods).

When a relatively small number  of LED fixtures (less than about 20) or short lengths (less than about 200 feet) are employed, voltage loss is minimal and calculations are not needed. But when systems become larger, or when higher wattage incandescent fixtures are included in the system, voltage loss may become considerable.

Incandescent lamps require between 10v and 12v for acceptable performance. LED's vary greatly in acceptable voltage range. This new calculator (beta version) enables the contractor to enter fixture information and predict voltage loss to ascertain whether or not voltage taps need to be adjusted, or other system parameters need to be changed.

Another confounding factor with LED's is the fact that manufacturers' specifications usually indicate wattage-only (as with incandescents). A system plan, however, cannot be based on reported LED wattage alone. Since LED drivers contain electronic components, they present a "power factor" consideration. The power factor represents an alteration of the current that necessitates over-sizing the wire and transformer.

Where an incandescent lighting system can be planned according to:

 Watts = Volts x Amps

An LED system must be planned according to:

 Watts/(Power Factor) = Volts x Amps

For incandescent systems, installers simply base transformer size on total watts. For LED systems, installers need to base transformer size on volt-amps. This can be confusing since landscape lighting manufacturers typically identify their transformers in wattage. This identification is actually incorrect; transformers should be specified in volt-amps. For the purpose of moving forward with LED installations, installers may assume that, for example, a 900-Watt transformer is actually a 900 volt-amp transformer.

Since standards for LED specifications are still under development, most manufacturers fail to report LED energy data in volt-amps, instead they only indicate wattage. To properly size transformers and predict voltage loss, the installer must use volt-amp values. It should also be noted that some manufacturers' claims of wattage are actually based on a DC power supply. DC current is more efficient (about 10% greater) than AC current when powering LED's. With this in mind, installers should be conservative in their system plans, and include a 10 to 20% margin of error.

This new calculator includes a fixture lamp volt-amp calculator. The installer can input manufacturer data (if available) or make an estimate of volt-amps by selecting "Estimate" in the Power Factor column.. The "Estimate" value is a Power Factor of 0.8 - a conservative estimate.

Evaluating the Calculator
This calculator is a beta version, meaning that it is released for the purpose of gathering feedback. CAST Lighting invites lighting and electrical professsionals to download this calculator, enter test values and evaluate for ease of use, accuracy, and relevency.


(Document No. 00146: Created on: 09/05/12 Last modified on: 04/14/15)