Voltage Drop with Varying Wire Gauges

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glick

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None of the voltage drop resources I have found list what happens with voltage drop when the conductor size varies.

Let's say a 1A/120V motor has 18AWG leads that are 1' long.
Then the supply leads are 12AWG and are 50' long.

I know in this scenario, voltage drop is not that big of a deal.
I am more curious about instances when the differences are more extreme.

Let's say the motor has 24AWG leads and the supply conductors are 10AWG.
(Yeah, I know 24AWG is not large enough for the load, just ignore that for now)

I have heard people say to just average the results, but it would seem to me that the smaller conductor would act as a weak link or choke point and would cause much more voltage drop than an average of the two voltage drops.

Thank you for your help!
 
mivey

mivey

Senior Member
glick said:
None of the voltage drop resources I have found list what happens with voltage drop when the conductor size varies.

Let's say a 1A/120V motor has 18AWG leads that are 1' long.
Then the supply leads are 12AWG and are 50' long.

I know in this scenario, voltage drop is not that big of a deal.
I am more curious about instances when the differences are more extreme.

Let's say the motor has 24AWG leads and the supply conductors are 10AWG.
(Yeah, I know 24AWG is not large enough for the load, just ignore that for now)

I have heard people say to just average the results, but it would seem to me that the smaller conductor would act as a weak link or choke point and would cause much more voltage drop than an average of the two voltage drops.

Thank you for your help!
Click to expand...
When wire sizes change, I make a sequence calculation (drop across 1st conductor, then drop across second conductor, etc). The drops for each section add, for the most part.
 
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gar

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Location
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EE
101206-0915 EST

It is quite simple. Calculate the resistance for each part of the path. There could be a 100 different segments and it would not change your procedure. Add all the resistances. Determine the current flowing. This means you determine the total impedance of the circuit to calculate the current. Or just measure the current. Your wiring also has inductance, but for simple estimates that is usually ignored. Then multiply that summed resistance by the current. You may also want to take into account the wire temperature in different segments.

This is all basic simple electrical engineering circuit analysis.

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