# How much voltage drop is acceptable at 120 volts?

4 of the National Electrical Code specifies that for typical efficiency, a voltage drop of 5% at the furthest receptacle in a branch wiring circuit is permitted. In a 120 volt 15 amp circuit, this means that when the circuit is fully loaded, there should be no more than a 6 volt decrease (114 volts) at the farthest outlet. This does not include any voltage drops within individual appliances such as lights, heaters, and air conditioners.

5 As long as you aren't exceeding maximum power limits, there's no reason why voltage reduction shouldn't be done effectively. For example, if you're using reduced-voltage circuits because your home was built before 1990, when they were required by law, then you should still be able to rely on these circuits to provide enough current to all parts of the house even when they are being used heavily. In this case, reducing the voltage would be beneficial because it would allow you to use smaller wire than if the circuit was set up for full voltage.

6 Finally, if you're concerned about voltage loss, try not to load down particular branches excessively. For example, if one branch of an extension cord has several heavy appliances plugged into it while another branch is empty, there will be less voltage available to the heavy load if both branches are at 120 volts than if one branch is at 240 volts and the other at 120 volts.

## What is the maximum recommended voltage drop for a branch circuit?

Five percent The NEC advises that the maximum total voltage drop for both the feeder and branch circuit not exceed 5%, and that the maximum voltage drop for either the feeder or branch circuit not exceed 3%. (Fig. 1). If you need more than one outlet per circuit, use separate circuits if possible to avoid exceeding the voltage drop limit.

In most cases, a single-outlet branch circuit can handle up to 3% voltage drop without violating the limit. But if you want to be sure, add an extra conductor to provide an additional outlet in case something goes wrong with the first one. Then it only needs to handle 1% of the rated capacity of the load in order to stay within limits.

Branch circuits are designed to supply power to different parts of a building. The term "branch" refers to the fact that they divide into separate circuits to serve different areas. Each branch circuit must have its own breaker in a panel located near where it will be used. Power companies usually won't send more current into a branch circuit than it was designed to handle. So if you plan to use your branch circuit to supply much more than its normal share of the house load, you'll need to upgrade to a larger size wire or replace some of the loads on the circuit.

## How big should a voltage drop wire be?

Frequently, voltage drop calculators would push you to increase wire size at a 3.01 percent drop—the lower size would compute to a 3.35 percent drop, which is completely good. 4.15 percent is OK. 5.03 percent is allowed. The rule is concerned with the overall voltage drop from the meter to the final outlet; it should not be allowed to exceed 8% unless there is a compelling justification. Voltage drops greater than this amount can cause problems for some appliances and equipment.

In general, cable should be large enough so that no more than 30-40 volts difference exists between ends of cable run. If voltage drops below 20 or 30 volts over long distances, insulation may need to be replaced on the cable. Old wiring needs to be checked for damage when replacing old plumbing or heating systems. Old wiring can be damaged by water or other elements, which can lead to electrical shorting if not repaired.

The voltage drop across any single conductor within the cable cannot be greater than 4.4 volts. For example, if one end of the cable has 5 volts and the other end of the cable has 2.5 volts, then the actual voltage across the cable is 7.5 volts, which is less than 10% of the available voltage, so it's within the acceptable range.

Cables used in power distribution should be large enough to carry all the current they are expected to carry. Small cables become hot during transmission of electricity because of the resistance of their conductors. Hot cables reduce the efficiency of your system and may cause burning.

## Are 110 and 120 volts the same?

The words are interchangeable because transmission losses and power dips can lower the 120-volt electricity delivered by the power provider to as little as 110 volts by the time it reaches a receptacle. Most receptacles have a genuine voltage midway between these two figures. For example, a household circuit will usually be either 115 or 120 volts depending on which side of the middle point you measure it on.

This is different from house current which always stays at 120 volts no matter what position the meter reads in between pulses. Power surges caused by storms or other external factors can also bring about momentary drops in voltage. This happens more with 110-volt electricity and needs to be taken into account when using equipment that relies on a steady voltage level.

As long as you don't need perfect consistency, there's no reason to worry about which term is used for 110 volts vs 120 volts. They're equal opportunities offenders here!

## At what length should you worry about a voltage drop?

Under fully loaded conditions, it is suggested that the voltage loss be less than 5%. However, most power supplies only operate at this level for several seconds before they must switch to an alternative source of power. For example, if the supply voltage dips below 8V, then the 8V line will trigger a reset of the controller.

If the voltage drops too low for too long, such as during a power outage, then the equipment attached to the supply may be damaged. Therefore, it is important to include appropriate protection devices on all power supplies. These can be in the form of surge protectors or circuit breakers.

Power supplies have some inherent resistance when delivering power from one part of the circuit to another. This is because every conductor has some amount of resistance, and all parts of a circuit are not always connected together. So even though you are not using any more current than you were before, there will still be some loss due to resistance.

The voltage across any resistor decreases over time as energy is lost to the environment. A power supply delivers constant voltage, so if the input voltage drops, then the output voltage will also drop. This is why power supplies need regular maintenance to ensure that their internal components are working properly.

## What voltage drop is acceptable in the UK?

Maximum voltage drop values are allowed in BS7671 Table 4Ab I 3% for lights (6.9V) or 5% for other purposes (11.5V). These values may need to be adjusted depending on what mode you are operating your lamp in. For example, if you are using a dimmer switch then this will affect how much voltage is dropped across it each time you switch off a light so care should be taken not to exceed these limits.

The voltage across any two conductors should not be more than double the supply voltage between them. This means that if you connect a cable from a power outlet that carries 100 volts between its wires, then no conductor within the cable can carry 200 volts or less. Any conductor within the cable can only carry 100 volts or less.

Power outlets in the UK carry alternating current (AC) at 110 volts between their hot and neutral wires.

#### About Article Author

##### Kenneth Carter

Kenneth Carter is a self-proclaimed gadget guy. He's got an eye for the latest technology and knows all about what's going on in the world of gadgets. Kenneth spends his time researching and writing articles about the latest and greatest gadgets so that readers like yourself will have an expert resource at their fingertips when they need it.

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