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Understanding Voltage Drop

Understanding Voltage Drop

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A voltage drop is the reduction in voltage in an electrical circuit that occurs when the current is passed through the wire. Essentially, when a current flows about a circuit, there is a drop in energy potential across the circuit. Wires carrying current always have an inherent degree of resistance, or impedance, to that current’s flow. The greater resistance of the circuit, the higher the voltage drop that occurs. How do you know when a voltage drop becomes inefficient or even unsafe? Here’s a summary of what’s considered a normal voltage drop and when it’s considered in excess and therefore problematic.

Voltage Drop Parameters

When a certain amount of energy is lost to the wire that’s carrying it, or voltage drop, is a normal electric function within certain parameters. Depending on the type of circuit, its amperage, its length, the type of conductor, and its load, national and local electrical codes set guidelines for the maximum voltage drop allowed in a circuit. This not only ensures efficient distribution of energy and proper operation of the equipment being powered, but it also speaks to electrical safety issues. Generally, for power efficiency, the National Electric Code (NEC) holds a recommended standard of 5% maximum voltage drop.

Causes of Excess Voltage Drop

When excess voltage drop occurs, it’s caused by too much resistance in the wire, which lowers the amount of power that reaches the “load,” or what’s drawing the electricity from its source. This is typically caused by a wire that doesn’t meet code standards, meaning it isn’t appropriate for that particular circuit. A high-resistance connection can also be caused by poor splicing, loose or intermittent connections, or corroded connections within the circuit.

Consequences of Excess Voltage Drop

When the voltage drop is too steep, it can cause the load to work harder with less voltage pushing the current. Overall, this leads to poor efficiency and wasted energy. A low voltage to the equipment being powered can also cause improper, erratic, or ceased operation, which can ultimately result in damage to the equipment. Even more alarming, heating a high-resistance voltage connection can result in a fire if it’s in contact with a combustible material or there isn’t enough air flow to dissipate the heat.

In electric design and power transmission, voltage drop needs to be taken into consideration. Electricians can always use various techniques to compensate for the effect of voltage drop, the most simple being to increase the diameter of the conductor between the source and the load, thereby lowering the overall resistance.


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