## Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.

## Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.

(OP)

The NEC recommends a maximum voltage drop (VD)of a total of 5% across feeders and branch circuits, and 3% across the branch circuit alone implying 2% on the load circuit.

Since most loads can operate efficiently at 95% of the nominal nameplate voltage, what is the relevance of meeting the 3% voltage drop in the branch circuit?

Since most loads can operate efficiently at 95% of the nominal nameplate voltage, what is the relevance of meeting the 3% voltage drop in the branch circuit?

## RE: Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.

## RE: Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.

## RE: Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.

Of that 5%, no more than 3% may be on branch circuits.

If the voltage drop on the branch circuits is less than 3% the percentage voltage drop on the feeders may be increased as long as the total does not exceed 5%.

If the voltage drop on the feeders is less than 2%, the voltage drop on the branch circuits is still limited to 3%, and the total voltage drop will be less than 5%.

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Ohm's lawNot just a good idea;

It's the LAW!## RE: Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.

- Branch circuit:from the transformer to the main distribution panel........ 4%VD (EXCEEDED 3%)-Load circuit:from the main distribution panel to the load.........................1%VDTOTAL VOLTAGE DROP FROM THE SOURCE TO LOAD.........................5%(Meet max. %VD threshold)## RE: Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.

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Ohm's lawNot just a good idea;

It's the LAW!## RE: Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.

If you get the voltage at the gate of 114 you have to assure the furthest motor 108 volt [104 V sometime]

Because, sometime, if there is a problem with power delivery [for short time] the range B is the minimum. So, the law permits a service voltage of 110 V. In this case 120-104=16 V[104/120=86.7%]

## RE: Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.

Hi Waross, I'm not sure of the CA code, but the NEC in the US is not mandatory for voltage drop issues and electric utilities are legally exempt from following the NEC. The voltage issue is not a code violation but rather an efficiency issue.

From the efficiency standpoint, if the load operates in the acceptable efficiency range within -5% of the equipment nameplate, still I have difficulty understanding the rationale for maintaining 3% VD in the branch circuit considering the load operates satisfactorily well even if exceeding the 3% on the branch circuit.

## RE: Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.

nominal 2-wire single phase system has

1) Nominal utilization voltage = 115V

2) Maximum utilization voltage = 126V

3) Minimum utilization voltage = 108V

The total 5% is based on the above limits.

Hence, it is designer's responsibility to ensure the above voltages always at the terminals of the utilization equipment.

## RE: Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.

## RE: Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.

cuky- I had assumed the 3%/2% split was typically included so that the design of the branch circuit was somewhat independent of the load circuit. Although the FPN states that this split is one possible way to have reasonable efficient operation, it leaves open the possibility that there are other alternatives available for reasonably efficient operation.

In most cases I assume the actual voltage drop is lower than the code calculated voltage drop due to lower loading. I would be kind of curious how the actual voltage on a building designed for a 4%/1% split would compare with a building designed for a 3%/2% split. Designing an installation with a alternative 4%/1% split might leave a trap for a future engineer during renovation project if they assume a new load circuit can have a 2% voltage drop.

Real world efficiency is also impacted by other variables like harmonics, phase voltage imbalance, ambient temperature, and utility side voltage variations. I suspect the overall efficiency would be poor if every factor was simultaneously at the extreme of the allowable range.

## RE: Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.

The reason I see is that main feeder lines are seldom changed/ upgraded while conductors servicing the final loads could be used for other purposes or load added to existing panels. That is why the guys before us have decided it should be practical to set a 2% limit on the VD from the source to the distribution board and have chosen a 3% VD limit (more lenient than the upstream limit).

## RE: Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.

But, if you're checking all the loads and determine the voltage drops reaching the loads are good then that's also fine.

## RE: Relevance of 3% voltage drop on the branch circuit vs. a total of 5%.