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Discussion Starter · #1 ·
Here's a couple of things I've seen in the field:

20A lighting circuit, #6 wire used because of the distance...then a photocell was installed next to the panel.

20A lighting circuit, #8 wire starting from the contactors, increasing to #2 wire at light poles at far end of parking lot.

Both of these seem as if they would work, but will they ?
 

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Feel like I'm about to get jumped... But here goes,

Scenario #1. No problem here( assuming #6 was sized for the actual distance), the voltage drop across the photocell is minimal... The distance is the factor. So the #6 leaving the cell and going all the way to wherever it goes is better than smaller wire.

Scenario #2. Sounds like an oops to me... The #8 had unacceptable voltage drop, the #2 was added at the end to maintain reasonable voltage to the end of the circuit. My opinion is the conductor should have been sized correctly and consistently from source to load.
 

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Discussion Starter · #4 ·
I was pretty sure that the short length of the photocells leads would not cause a problem. The #6 went to the ground box on opposite side of bldg, then #8's split off in different directions.

The second one seemed to have been done exactly backwards #8, then #6, then #4, then finally #2. I didn't measure the distances exactly.

As a general rule of thumb, at what distance would any of you start calculating for voltage drop ?
100' ? 150' ?
 

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Depends what the load is... Motor loads I start to consider voltage drop when the 100' mark is close. Few lights and an outlet in a shed 100' away... I don't really worry too much about it honestly, unless it's stupid far, say over 200'. No idea if I'm right on this! Just the way it was when I was learning the trade. There's a voltage drop app for iPhone that I have used for landscape lighting projects that's very handy.
 

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Value engineering. It's cheaper to run the smaller conductors for as long as you can and transition to a larger size to keep voltage drop within the engineer's specs. On small installations, the material costs aren't as crucial, but on a big project with miles of copper it makes a big difference
 

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The phone company runs larger wire as they get further away. Starts out as 24AWG then to 22AWG then well you get the idea. I always thought it was backwards too. The engineers spec it that way. I guess a 300pair of 24 is much cheaper than a 300pair of 19AWG which is the largest wire they use, odd number.

TWN
 

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This is interesting, and makes sense. I'm wondering how to calculate smaller to larger. I've done larger to smaller, that always seemed logical to me, but cost wise for bidding parking lot jobs....this could come in handy.
 

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Value engineering. It's cheaper to run the smaller conductors for as long as you can and transition to a larger size to keep voltage drop within the engineer's specs. On small installations, the material costs aren't as crucial, but on a big project with miles of copper it makes a big difference
A small piece of #12 only 4 feet long will have less voltage drop then 4 miles of 4/0 cu.


Another example of that I frequently see are road way lights. 2/0 might be used at the beginning run, but as fewer lights are up the stream drawing less current less voltage drop is present do the conductor drops to #1 #2 , #3 ect but still within limits for voltage drop.
 

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Here's a couple of things I've seen in the field:

20A lighting circuit, #6 wire used because of the distance...then a photocell was installed next to the panel.

20A lighting circuit, #8 wire starting from the contactors, increasing to #2 wire at light poles at far end of parking lot.

Both of these seem as if they would work, but will they ?
It seems to me that that is kind of like running a one half inch diameter water hose for a distance and then increasing the size of the hose to three quarters at the end. Am I missing something?
 

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Another example of that I frequently see are road way lights. 2/0 might be used at the beginning run, but as fewer lights are up the stream drawing less current less voltage drop is present do the conductor drops to #1 #2 , #3 ect but still within limits for voltage drop.
I don't understand your example is the opposite of the second scenario and what bt said.

I am really confused as to why it would be good at 60 hz to go from smaller wire at the source to larger at the load. If you an big John agree I must be wrong, but why?
 

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I don't understand your example is the opposite of the second scenario and what bt said.

I am really confused as to why it would be good at 60 hz to go from smaller wire at the source to larger at the load. If you an big John agree I must be wrong, but why?
You are not wrong.
 

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I don't understand your example is the opposite of the second scenario and what bt said.

I am really confused as to why it would be good at 60 hz to go from smaller wire at the source to larger at the load. If you an big John agree I must be wrong, but why?
Not necessarily one load on these circuits. They can serve outlets earlier in the run where voltage drop is not an issue and then transition larger ones where voltage drop comes into play.
It seems odd to do this but I've seen engineers spec it this way time after time, so I imagine they have crunched the numbers and figured out a way to save some coin by doing it
 

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Not necessarily one load on these circuits. They can serve outlets earlier in the run where voltage drop is not an issue and then transition larger ones where voltage drop comes into play.
It seems odd to do this but I've seen engineers spec it this way time after time, so I imagine they have crunched the numbers and figured out a way to save some coin by doing it
I can't possibly know everything...just ask my wife. However, How can someone restrict ANY energy at the source and expect to bring it up...down the line somewhere?
 

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I can't possibly know everything...just ask my wife. However, How can someone restrict ANY energy at the source and expect to bring it up...down the line somewhere?
The end load sees the total resistance of the circuit. It wouldn't matter if you reversed it and put the larger wires near the source, the total resistance would be the same
 

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RIVETER said:
I can't possibly know everything...just ask my wife. However, How can someone restrict ANY energy at the source and expect to bring it up...down the line somewhere?
I think the object isn't to bring the voltage back up, it's just to prevent any further voltage drop by lowering the resistance of the wire further from the source.
 

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None of these explanations show that it is better, cheaper, or even as good as just run your wires from larger to smaller. The only thing I am hearing is "Some guy speced it. Must be better".
 
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