Calculating Voltage Drop

[cambruzzi]

Voltage drop is determined by multiplying the total watts on the cable by the total length of cable and dividing by the cable constant. (These constants are listed below.)

(TOTAL WATTS x TOTAL LENGTH) / CABLE CONSTANT


Important! When most of the load is at the far end of the run, multiply constant by 2.


Total Watts= Sum of wattage for every lamp on one piece of cable.

Cable Length= Length of cable used (in feet) from the transformer to the fixture for which you are calculating voltage drop.

Cable Constant= Indicates thickness of copper wire. The thicker the wire, the lower the conduction resistance and the lower the voltage drop.

Wire Size & Cable Constant

#18= 1380

#16= 2200

#14= 3500

#12= 7500

#10= 11,920

#8= 18,960

How is the voltage determined at each lamp?

Voltage at each lamp is determined by subtracting the voltage drop at each lamp from the voltage at the transformer. The voltage at the transformer will depend on:

Which voltage tap is being used (11 volt, 12 volt or 13 volt).

The total load on the transformer.

the voltage feed to the transformer.

Try to locate the transformer in the most central location possible. Voltage drop can be controlled by:

Using the proper voltage tap on the transformer.

Center feeding to the load of each run.

Using proper cable size.

Using fewer fixtures on a cable run.

Using lower wattage lamps.

Please post any question or specific situation and we will get right back to you.