wire guage with DC voltage

[mark sonnier]

Where I work at we are using a 24VDC power supply with 12.5A capacity. I'm looking for a chart or information that will give me the coorelation between DC power, length of wire and current capacity for the correct wire guage to use. The power supply is used to run motors as well as motor controller boards. An information would be a great help.

 

[iwire]

Re: wire guage with DC voltage

Try this Free download from the Mike Holt Site

Windows Voltage Drop Calculater.

It has options for doing DC

 

[bphgravity]

Re: wire guage with DC voltage

Article 430 of the NEC covers requirements for DC motors and controllers, but nothing that small. What is the actual operation of these motors? Table 8 of the NEC shows resistance of condutors in DC, and standard VD calculations can also be used for DC.

 

[physis]

Re: wire guage with DC voltage

I don't have a copy of the NEC so I can't look it up. But. Unless your going any significant distance, I think 12AWG should do. I really don't think you'ld need 10 gauge.

 

[iwire]

Re: wire guage with DC voltage

Using this info in the voltage drop calculator referenced above tells us no more than 25' on 12 awg copper before we hit 5% voltage drop

Move up to 10 awg and you can go 38' before 5% voltage drop.

Move to 8 awg and you get 61'

With lower voltages, voltage drop becomes more of an issue.

 

[dereckbc]

Re: wire guage with DC voltage

You need to be very careful with low voltage DC circuits. Voltage drop is critical. For a 24 VDC you do not want any more than 1 VDC. Use this formula to determine cable size at 1 volt drop. Do not use table 310.16 or you will more than likely encounter too much voltage drop.

CM = (22.2 * I * L) / 1

CM = Circular mills of cable required
22.2 = K for copper at DC
I = Max Load current
L = One way cable distance
1 = 1 volt loop drop

 

[physis]

Re: wire guage with DC voltage

Thank you Iwire and Dereckbc for pointing out voltage drop over wire length. Based on the description I was considering the problem to be an issue inside of a piece of equipment where 10 ft. would be a significant wire run. In a different situation 12 gauge could have been bad advice.

My apologies Mark Sonnier.