Calculate Voltage Drop

Have you ever noticed a time when some of your home appliances turn on but seem to lack enough power to function well?  You are seeing the effects of what is called a voltage drop which is caused by a reduction in the voltage or current in the electric circuit.   Too much drop in voltage is a waste of energy and can actually damage equipment or the wire itself.  Voltage drop would increase with the length of wire being installed.  Generally, the longer the wire the higher the voltage drops.  In addition, if the wrong wire gauge is used, it can cause an even higher voltage drop at the load end.

If you have basic understanding of circuits, you can calculate voltage drop manually and arrive at an educated approximation.  Below is a simple example to illustrate how to calculate voltage drop.  There are certain standards or constants that can be referred to when you calculate voltage drop.  One such matrix was prepared to calculate for the voltage drop values when using 100 feet-length of paired wires, taking into consideration the wire gauge and the load current.  However, for purposes of illustration, we will only select appropriate values for each situation and not discuss the entire matrix and values contained therein.

Example:  If you have 1 AMP of load current, using an 18 AWG wire gauge, calculate voltage drop at the load end if the paired wire is 350 feet in length?

• In reference to the prepared matrix for a 100 feet long wire, look for the value that corresponds to 1 AMP and 18 AWG.  The corresponding figure in the matrix is 1.27 and that is the voltage drop for a 100 feet long wire.
• Given the example is for a 350 feet long wire, we need to divide 350 by 100 and multiply the quotient to 1.27;  the product would equal to 4.47 volts which is the actual voltage drop.

If you find manual computation tedious or if you are afraid of miscalculating, there are several websites that offer online voltage drop calculators.  These are simple to use and can be used for free.  All you need to do are the same information discussed in the example above – wire gauge, wire run length, load current (AMP)  and the voltage drop value found in the matrix.  You simply need to input the data and press “calculate” and you will have the voltage drop figures in an instant.  The complete voltage drop matrix is also available online.