Calculating wire size for 12 VDC. vs. 110 VAC?

[oarfish]

Hi everyone, Is that true that 110V AC will create more heat in a conduit than a 12V DC would?? -provided that the currents are the same of course. Is there an equation I could use for sizing wires for the 110 VAC /60 hz and also for the 12 VDC automotive application? It has been more than 35 years since I was in electronic school in Hungary back in the 70's. I forgot all the details. Any help would be appreciated. I need an equation for the heat created as well. Thanks!! My understanding is that I can use less wire for more current in the 12 VDC. Am I correct?

 

[MikeMl]

The losses are essentially the same at 60Hz as at DC. Here is a calculator.

 

[Reloadron]

Westlake, Ohio? Greetings to across the Cuyahoga. Bedford Heights here.

Use the calculator Mike suggest and any questions, just ask.

Ron

 

[Dean Huster]

The down-side is that for a given load (in watts), the wire size for the 12v system will be substantially larger, necessitating larger conduit in most cases. And for a given length from source to load, the higher voltage system can use smaller wire as the current is much lower producing smaller IR losses. Rarely is a low voltage system for high power a good choice when higher voltages are available.

 

[Blars]

You need better insulation at higher voltage. For the same current, the voltage drop on the wire will be a larger portion of the power, so you may need larger wire at low voltage. 1v loss is less than 1% of 120v, but more than 8% of 12v.

 

[oarfish]

Thanks for the info. I understand and agree but I found some links for boating and automotive current/wire size charts that had tables allowing much smaller gauge wire for same current than 110V would. I was seeking these forums opinion since nobody seems to know for sure in my circle. I was not able to post the links here however.

 

[oarfish]

I still would like to know the equation calculates wire size/length/voltage drop. Anyone?

 

[Reloadron]

I see where a link like this could be what is talked about. For a short run of 20 Amp service they seem to suggest for example AWG 18 up to about 7 foot then work up a little reaching AWG 12 at 20 feet and AWG 10 at over 25 feet. Personally, considering wire size and cost if I am running 20 amp service I am going to use AWG 12 and if there is excessive length, I move to AWG 10.

When it comes to a long run you look at the resistivity for the conductor type (the rho) and calculate what the line loss would be.

Good connections and quality wire are paramount unless you want your vehicle to burn down to the road surface or your boat to the waterline. I won't even touch aircraft but Mike may have a comment on that.

<EDIT> As to firm calculations (I just saw your last post) they are covered in IEC 60287. This link provides an overview. The problem is all the variables. This is also why I believe people relate well to published charts and standards as to wire gauge and ampacity. This gets into a science and math unto itself.</EDIT>

Just My Take
Ron

 

[MRCecil]

The links Ron has provided should take care of your questions on the 12V automotive side. Regarding the other part of your question about 120VAC, conduits and sizing you might want to look at this link - - for a conduit max. fill chart.

Good Luck and Happy New Year!

 

[KeepItSimpleStupid]

This https://www.electro-tech-online.com/custompdfs/2010/12/WIREGAUGE.pdf is just one way to calculate, but remember that the length of wire is twice the distance to the load.

There are other ways based on the basic formula R=pL/A where p = the Greek letter rho. p is the resistivity of the material, L is the length and A is the cross sectional area. Again remembering that L is usually twice the distance. p changes if the conductor is aluminum or copper. Cross section area is easier to compute using metric wire sizes. The basic unit of p is ohm-cm or ohm-(length).
Wire tables use circular mills as the unit for cross sectional area. It does simplify to an easy equation.