Voltage drop

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nickelec

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I'm having a bit of a hard time trying to grasp the fact of a current situation I have going on right now.. 300 ft run of 2 sets of 350s fused at 800a
Testing on the end of the line I get a reading of 203v phase to phase on. 120/208 system and 114v line to neutral.
So my calculations say that 350s are to small so what I could do is drop down the fuse size but I know that won't solve the voltage drop.
I can't understand what is causing the voltage drop I'm thinking that no matter what size wire was ran the voltage drop would still occur

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nickelec said:
I'm having a bit of a hard time trying to grasp the fact of a current situation I have going on right now.. 300 ft run of 2 sets of 350s fused at 800a
Testing on the end of the line I get a reading of 203v phase to phase on. 120/208 system and 114v line to neutral.
So my calculations say that 350s are to small so what I could do is drop down the fuse size but I know that won't solve the voltage drop.
I can't understand what is causing the voltage drop I'm thinking that no matter what size wire was ran the voltage drop would still occur

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Voltage drop is entirely a function of the total current between two points and the effective parallel resistance between those two points.
Resistance can include resistance of poorly designed or executed terminations and splices as well as the calculated resistance in the conductor runs themselves.
You did not say what the current was when you measured the 114/203. Nor did you say what the measured voltage was at the source end of the circuit. Without both of those we cannot tell you whether the voltage drop you see is normal or unexpected, nor what you can do about it.
Voltage drop is measured from the actual system voltage, not the nominal system voltage, so not all cases of low voltage at equipment are entirely the result of voltage drop in the circuits feeding that load.
If you are talking about voltage drop rather than just low voltage, then larger wires will always be better.
 
Be wary of oversimplified voltage drop calculations. You need to consider more than just the resistance of the wire; i.e. reactance and power factor of the circuit. Send me a PM with the details and I’ll calculate it for you.
 
These measurements were taken at a new sub panel with no load connected

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There was no current draw nothing is connected to the panel yet

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nickelec said:
These measurements were taken at a new sub panel with no load connected.

There was no current draw nothing is connected to the panel yet
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Then you should be measuring the same lower-than-nominal voltage at the feeder source, which means your issue may be caused by voltage drop ahead of this point.

Keep measuring upstream until you find greater readings.
 
nickelec said:
There was no current draw nothing is connected to the panel yet
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Then this isn’t a voltage drop issue with your installation. It’s a voltage regulation problem from wherever you are connecting your feeder. This could be due to an overloaded transformer, improper tap settings, upstream voltage drop.
 
nickelec said:
I'm having a bit of a hard time trying to grasp the fact of a current situation I have going on right now.. 300 ft run of 2 sets of 350s fused at 800a
Testing on the end of the line I get a reading of 203v phase to phase on. 120/208 system and 114v line to neutral.
So my calculations say that 350s are to small so what I could do is drop down the fuse size but I know that won't solve the voltage drop.
I can't understand what is causing the voltage drop I'm thinking that no matter what size wire was ran the voltage drop would still occur
Click to expand...

As others have stated the problem isn't at the panel since there is no load. You didn't say where the 300' run originates, the problem could even be upstream of that. Also two sets of parallel 350's are no good for 800 amps. (310*2=620 amps)
 
nickelec said:
There was no current draw nothing is connected to the panel yet

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Voltage won't drop when there is no current flow. This just means wherever you connected to is already a little low for some reason and that it can drop even more at the end of the feeder in question once you start to load it.
 
kwired said:
Voltage won't drop when there is no current flow. This just means wherever you connected to is already a little low for some reason and that it can drop even more at the end of the feeder in question once you start to load it.
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And if the calculated load allows it, you can avoid pulling more wire by changing the breaker. Voltage drop may or may not be a real problem then.
 
nickelec said:
The voltage at the supply is normal 120/208

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If the voltage at the supply is normal and the voltage at the unloaded branch is low, then either there is a transformer along the way or there is significant current and voltage drop in the feeder which is supplying that branch.
If there is no current and no magnetic circuit like a buck transformer, then there can be no voltage drop from one end of the wire to the other.
 
GoldDigger said:
If the voltage at the supply is normal and the voltage at the unloaded branch is low, then either there is a transformer along the way or there is significant current and voltage drop in the feeder which is supplying that branch.
If there is no current and no magnetic circuit like a buck transformer, then there can be no voltage drop from one end of the wire to the other.
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No matter how long the run is or the size of the wire?

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Voltage drop

nickelec said:
No matter how long the run is or the size of the wire?

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You need to be drawing current to drop voltage. An open circuit feeder in your case will have no voltage drop.
 
nickelec said:
No matter how long the run is or the size of the wire?

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It's like having a water pipe a mile long. The pressure at both ends will be the same till you open the faucet, and you wouldn't notice if the pipe is too small if you all you did was crack the faucet open enough to let a trickle of water out.
 
ActionDave said:
It's like having a water pipe a mile long. The pressure at both ends will be the same till you open the faucet, and you wouldn't notice if the pipe is too small if you all you did was crack the faucet open enough to let a trickle of water out.
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The only time the pressure would be different between the two ends would be if one end of the pipe was higher than the other. In other words unless some sort of voltage generator was operating between the two ends of the wires.
Electrons flow uphill with hardly any problem at all. :happyyes:
 
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