Interesting Voltage Drop Information

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iwire

iwire

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I went searching for some voltage drop information here based on the 2002 NEC.

Here is part of it.


" CALCULATIONS FOR VOLTAGE DROP OF A FEEDER, OR A BRANCH CIRCUIT ?

?Special Note? The FPN Notes in the NEC are considered to be advisory, only.

If you adhere to the NEC requirement considering voltage drop.

The NEC requires the conductor to be able to carry the load, as per Article 220 PARTS B & C & D for feeders, and as per Article 210-19 for branch circuit conductors. Article 220 parts B, C, & D, calculates the load on a conductor at 100% for a non- continuous load, and at 125% for continuous load

PERIOD.

The NEC speaks nothing about giving a break for consideration of a loss of power, due to a voltage drop, that decreases the current carrying capacity of the conductor used. Therefore the NEC expects a full amount of power, [voltage], at ?end of line?.

Therefore the NEC requires that there will be no voltage drop allowance at all. You will find in ARTICLE 90-4 in the NEC that ?judgment calls? are up to the Authority Having Jurisdiction. Therefore, the Authority Having Jurisdiction has the authority to allow the use of the FPN note speaking of 3% on a branch, or feeder, and with a total voltage drop of 5% on the feeder, and branch combined. This NEC FPN Note can be used as an allowance for you to use that is within the authority of his judgment. Otherwise the NEC flat says that the conductor must be able to carry the load as computed in Article 220.
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iwire said:
I went searching for some voltage drop information here based on the 2002 NEC.

Here is part of it.
Click to expand...

But, the following pretty much sums up the fact that it only an opinion. and he is not very sure of it at that. :grin:

THE AUTHOR AND/OR PROVIDERS OF THIS DOCUMENT ASSUMES NO RESPONSIBILITY FOR ERRORS OR OMISSIONS, NOR IS ANY LIABILITY ASSUMED FROM THE USE OF THE INFORMATION CONTAINED IN THIS DOCUMENT, BY THE AUTHOR AND/OR PROVIDER.
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Roger

 
I don?t know where to begin with this one. Perhaps I?ll start here:
The NEC speaks nothing about giving a break for consideration of a loss of power, due to a voltage drop, that decreases the current carrying capacity of the conductor used.
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The current carrying capacity of a conductor has nothing to do with the voltage applied to it, nor with the voltage that is dropped along its length.
Therefore the NEC expects a full amount of power, [voltage], at ?end of line?.
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Clearly, the author does not know the difference between power and voltage.
Therefore, the Authority Having Jurisdiction has the authority to allow the use of the FPN note speaking of 3% on a branch, or feeder, and with a total voltage drop of 5% on the feeder, and branch combined. This NEC FPN Note can be used as an allowance for you to use that is within the authority of his judgment.
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The NEC does not convey to anyone the ?authority? to use a Fine Print Note. 90.5(C) explicitly says so.
Otherwise the NEC flat says that the conductor must be able to carry the load as computed in Article 220.
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Yes it does, and the AHJ?s thoughts with regard to an FPN neither add to nor detract from that requirement. But again, neither voltage nor voltage drop has an impact on ampacity.
 
The NEC speaks nothing about giving a break for consideration of a loss of power, due to a voltage drop, that decreases the current carrying capacity of the conductor used.
Click to expand...


How does voltage drop decrease the current carrying capacity of a conductor?:confused: :confused:

The whole thing looks like flawed logic to me.:rolleyes:


Edit: Yeah, what Charlie said! ( I type way too slowly)
 
Otherwise the NEC flat says that the conductor must be able to carry the load as computed in Article 220.
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The circuit can still carry the load and have a voltage drop. So if we base out calculation on 240 volts and the power company delivers 236 volts are we in violation??? Of course not-- there is always going to be fluctuations in voltage and ampacity, , to some degree, on circuits.

That being said I think it is wise to consider VD as most of us here do.
 
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