# COMMUNITY FORUM

GlenO

03:54PM | 07/31/00
Member Since: 01/25/99
Does anyone know how to figure when to go to the next wire size when running wire over a long distance? Thanks.

HOLLYWOOD

04:37PM | 07/31/00
Member Since: 02/19/00
I need to know total feet of wire 1 way and what you are powering...Total amp draw on circuit.
You need to run UL cable. This cable requires no conduit. There is no formula, only a process to which I need to know this information. I will check back

ElectrcBil

07:13PM | 07/31/00
Member Since: 07/21/00
There is a formula for Voltage drop. 2KIL/cm Where K is a constant for the type of wire being used (copper is 10.4) I is the amperage draw of the device at full voltage rating. L is the length of the wire one way. and cm is the circular mil area for the wire. If you rearrange the formula you get cm=2KIL/Vd where Vd is voltage drop. The N.E.C. allows for a 3% Vd. So if you have a 120v circuit with a 3% Vd the allowable Vd. is 3.6. If your device pulls 16 amps and is 300 ft away from your panel then your equation will look like this, cm=(2x10.4x16x300)/3.6volts which =27733.33cm If you check the N.e.c. chapter 9 table 8 the closest wire size to this circular mil area is #4 (always go to the next larger wire size). This is only an example. If you give me some idea of what you need to do i'll try to give you a better idea of what size wire to use.

HOLLYWOOD

05:14PM | 08/01/00
Member Since: 02/19/00
I believe copper is 12.9 @75*c. The K value will change with temperature.

ElectrcBil

07:20PM | 08/01/00
Member Since: 07/21/00
The "Ugly's Electrical reference Book" shows a Voltage drop Equation with a K value of [email protected]*C. The value I was using was for a temperature of 20*C from "Delmars Standard textbook of Electricity". It also states that for each degree rise in Celcius the K value will increase by .0039. Taking into consideration an increase of 55 degrees the value would increase by .2145 for a new value of 10.61. Why would these numbers very by so much from two different references? Hollywood please provide some insight if you know. I am very curious as to which is more accurate. Will check back later.

GlenO

12:01PM | 08/02/00
Member Since: 01/25/99
Thanks for responding. What I am putting in is a condensing unit and evap for a walk-in box. It's a 220 volt system 1 hp compressor, other than that that is all I know at the present time. The location is a 2 1/2 hour drive from me.

ElectrcBil

06:39PM | 08/02/00
Member Since: 07/21/00

HOLLYWOOD

02:06AM | 08/03/00
Member Since: 02/19/00
Bill as you know, sometimes different texts provide slightly information. I think that you are probably right and besides,...My field of expertise is in the HVAC industry. I think that you have done you homework and feel comfortable with your recomendation..

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