Length of Run and Wire Gauge


  #1  
Old 07-26-01, 03:59 PM
M
MKM
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I noticed in the back of Home Depot's Wiring 1-2-3 book that wire gauge should be increased depending on the length of run. In particular, it says that a 15 amp circuit is fine on 14 guage for up to 50'. From 50 to 100' it suggests 12 gauge and over 100 it suggests 10/2. Imagine my surprise after I roughed in a 95' long 15A circuit on 14/2.

Are these suggested values, or NEC specs?
What's the real impact here?
And, if I do have to run my 15A circuit on 12/2, can I still use 15A switches and receptacles?

Thanks...
...Mike

BTW, the chart was put out by the makers of Romex(r) brand cable.
 
  #2  
Old 07-26-01, 05:29 PM
rhhjr
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voltage drop

Mike, if your branch circuit ever pulls the full 15 amps, I calculate that the voltage drop would be 8.3 volts (one of the smart guys on this board should double check me on this). That's more than the 3.6 volts maximum recommended by NEC 210-19a. The effect ? Well, probably none, especially if you're just powering a few incandescent lights or don't pull a lot of amps on the circuit. Where you might have a problem is on one of those hot days when you utility is dropping the voltage they put out (a brownout), AND your long run on 14 AWG drops the voltage further, AND you are running a lot of amps on that circuit, AND you plug in something voltage sensitive (computer ?). Have you closed up the walls yet ? If not, I'd yank out the 14 AWG (you'll re-use it sometime in the future) and put in 12 AWG. (Note: even with 12 AWG, at 15 amps your voltage drop is still over 5 volts !) Yes, use your 15 amp switches and receptacles....rick
 
  #3  
Old 07-27-01, 03:08 AM
Wgoodrich
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I came up with 8.95 volts lost, probably in a decimal point in the calculation for the difference between us. You did good.

If this 14 awg wire is a branch circuit within a dwelling and is used for general use or general lighting. You did fine. If this 14 awg wire is a branch circuit serving receptacles in a laundry, bathroom, kitchen, dining, nook, then you did bad.

Rule of thumb is that on a normally loaded circuit you should be able to run 125' on a 120 volt circuit, 250' on a 240 volt circuit, or 600' on a 480 volt circuit. If you stay within these limits I wouldn't worry about hitting a voltage drop calculation. If you exceed these distance compared to these voltages then start checking for voltage drop problems.

Voltage drop is electricity that you paid for but didn't get to use. Voltage drop also affects life expectancy of motors, increased heat in equipment, dimming of lights, etc.

Now if you ran that 14 awg wire to the other end of your house you should be fine. However if you wife plugs in an iron for her ironing board you may experience dimming of lights. Usually this is no problem.

If it gets hot and you install an A/C unit in you window then I would run a new circuit to that A/C unit. If this A/C unit is run on this 14 awg 95' run your life expectancy of this A/C unit would be reduced due to the starving of electricity that it is designed to run on.

Yes you may install 15 amp rated receptacles and switches on a 15 or 20 amp branch circuit.

Hope this helps

Wg
 
 

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