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# Maximum run distance

#1
06-26-05, 07:29 PM
Bob10
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Maximum run distance

Is there a rule of thumb for determining the maximum distance I can run a #12/2 w/ground? (outdoors, direct burial). on a 20A breaker.
And how can I determine the maximum wattage that I can have on the line based on distance?
I am wanting to operate incandescent lighting that will total approximately 1400 watts.
Thanks.
Bob10

#2
06-26-05, 07:53 PM
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Generally, you establish the distance (usually fixed) and the load (wattage), and then you decide on the wire size needed.

#3
06-26-05, 08:00 PM
Bob10
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I understand that would be the way it would normally be done, however I have many variables or possibilities in this particular case (ie. location of lighting and distance from panel) and it is "cost" related where I locate the lighting.

#4
06-26-05, 08:16 PM
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Let me ask you another question. Are all these lights going to be the same distance from the panel, or will they be at increasing distances?

#5
06-27-05, 05:47 AM
Bob10
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at varying distances.
Light 1-300w .. 47'
Light 2-300w .. 62'
Light 3-300w .. 105'
Light 4-300w .. 118'
Bob10

#6
06-27-05, 05:56 AM
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The only problem I see with this is that the voltage will be less at each successive light on the run, meaning that the lights will be less bright. Incandescent lights tolerate voltage drop, so as long as you can live with this you will be fine. The voltage drop won;t be bad, and you may not even notice the light difference.

#7
06-27-05, 07:42 AM
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Not long ago someone posted in a thread on here a way to use 12-3 UF rather than 12-2 that would distribute the voltage drop so all lights would have equal brightness. I do not recall the details, but it involved using the red wire to create a loop from the 1st to the last light. Perhaps, assuming it is OK by code, that would be useful for the OP.

Maybe somebody remembers that thread, or knows what I am talking about.

#8
06-27-05, 08:11 AM
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Bob, given your distances and wattages, you won't have a problem using 12/2. Go for it.

#9
06-27-05, 11:43 AM
Bob10
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I'll be sure to post back.
Thanks for all the help.
Bob10

#10
06-27-05, 11:43 AM
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Bob10,

Ok...last minute light on the subject...light..get it...light..thehehhee...hmmm...ok...anyway..

If you ran 12/2 for 118' as you said and lets say the load is 1,440 watts at the end which is 12 amps......

The voltage drop would only be 5.6 volts or 4.7% in the circuit....so basically as john said....Run your 12/2....you will be fine...

#11
06-27-05, 11:48 AM
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Originally Posted by ElectricalMan
Bob10,

Ok...last minute light on the subject...light..get it...light..thehehhee...hmmm...ok...anyway..

If you ran 12/2 for 118' as you said and lets say the load is 1,440 watts at the end which is 12 amps......

The voltage drop would only be 5.6 volts or 4.7% in the circuit....so basically as john said....Run your 12/2....you will be fine...
ElectricalMan, how are you able to determine the voltage drop so specifically? Is there a formula which does this, or a table? Quite curious...

#12
06-27-05, 11:59 AM
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There are voltage drop calculators on the Internet at various sites. Google the term "voltage drop calculator" and you will find them.

Calculating the drop on a circuit like this is tough, as the current varies because the lights will be at different locations on the cable. Technically you would have to computer the voltage drop to the first light, then compute to the second light, then to the third, etc. However, that is more work than really necessary. If you go worst case (as if all the load was at the end of the run), you will be safe, since the actual drop will be less.

#13
06-27-05, 12:00 PM
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http://www.electrician.com/vd_calculator.html

I actually do most by hand in the field or use our ElecticalCalc....but us OLD school guys like to figure it by hand...lol....anyway many use the simple online calc I posted above.

Most of the time we total the entire load for the circuit in question and then do the math......as RAC said as well....in our systems we like to total the overall potential and then do the math on that because basically as RAC said with Incond. lights it can handle the drops better....and if you ensure the entire line on the max draw is fine...chances are the lights ahead of it will be fine also.

#14
06-27-05, 12:16 PM
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Man....RAC...........I wanted sx to think I was a mathmatical genius...lol.....ok I am pushing that a bit...lol...thehehe...

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