power cable size per distance ? 2

[scorney]

Hi, I Have a question about cable size?

How can we calculate the cable size when we know the circuit breaker to use. Let's said that we have a shelf powered by -48 Volts that have a 60 Amp circuit breaker on it and the length is 25 feet, should we use a regular 6Awg or because of the distance we should use 4 Awg.

how do we calculate this, per 1 Volt drop.

please explain!!!
Thanks in advance.

 

[franklin97355]

First you would need to know the draw of the equipment. your wire size depends on the amps drawn.

 

[scorney]

You're right Franklin,
Let's check with a 45 Amp drain when shelf is fully loaded.

How this will be calculate?

 

[wires]

I would go with 4 awg.

22*45*25/26300=.94

22 is a constant.

45 is the current in amps.

25 is the one way distance in feet.

26300 is the diameter in circular mills of 4 awg wire.

.94 is the approximate voltage drop.

 

[wires]

WHOOPS!

6 AWG is OK

26300 is the AREA in circular mils of 6 AWG.

4 AWG is 41700 which would give a drop of .59 volts.


Sorry!!

 

[scorney]

Thanks Wires,

Is there a web site that give us the diameter in circular mills for diferent cables? kind of a chart.

Thanks

 

[wires]

A nice table can be found at:

http://home.tampabay.rr.com/k4lk/info/wire.htm

I highly recomend getting a copy of Pocket Ref by Thomas J. Glover. It has saved me much time, effort and expense. Here is a URL to the publisher:

http://www.sequoiapublishing.com/pdt_pocketref3ed.htm

 

[butthead]

wires" would appear to be using a 3phase
motor calculation to calculate the wire size.

Vd (1Phase) = 2KIL/Cm
Vd (3Phase) = 1.732KIL/Cm
Cm (1Phase) = 2{K}IL/Vd
Cm (3Phase) = 1.732{K}IL/Vd

in this instance I would think that using the
specific resistance would give more precision.

although the calculations appear to give similiar
results, an engineer might cringe at the usage.

check out this site

http://www.allaboutcircuits.com/vol_1/chpt_12/5.html

3phase
Voltage is -> 48volts
Amp load is -> 45amps
Length of cable is -> 25ft
Voltage drop is -> 1volts
Calculated size of cable in circular mils is -> 25136

Suggested cable or wire size is -> 6 awg (26240 circular mil)

1phase
Voltage is -> 48volts
Amp load is -> 45amps
Length of cable is -> 25ft
Voltage drop is -> 1volts
Calculated size of cable in circular mils is -> 29025

Suggested cable or wire size is -> 4 awg (41740 circular mil)

using Specific resistance

Cm = p(L/R)
Cm = 10.09(25 ft/0.011 ohms)
Calculated size of cable in circular mils is -> 22931

Suggested cable or wire size is -> 6 awg (26240 circular mil)

the voltage drop of this size (6awg) is calculated at
.433 volts

tomcruz.net