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I'm making a protoboard that will include three small sections of wire, around an inch long each, to go:

power source -> relay -> out

power source -> out

When the relay is on the wires will be carrying 12v 1.8amps

How can I determine the correct wire to use?

I've taken a look at the question Choosing the right type of wire? but didn't find info that helped my situation.

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Perrin255
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  • If knowing the ampacity of the wire, covered in the question you looked at, is not helping; then what do you mean by "correct wire?" – JYelton Sep 17 '13 at 21:12
  • I'm a beginner. The word "ampacity" is not mentioned in the question I looked at. A helpful answer would be: You need to know the ampacity of the wire against your requirement. You can calculate your required ampacity by ... xyz. I'm now off to research this info ... – Perrin255 Sep 17 '13 at 21:40

2 Answers2

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When making a project on protoboard or a custom PCB, here are some considerations for selecting wires that connect that board to other devices:

  • Current carrying capability (ampacity)

    What wire gauge is needed for the current? What voltage drop will the wire impose for the intended distance?

  • Voltage

    What voltage needs to be carried? Is the insulation appropriate?

  • Temperature

    What temperatures will the wires be exposed to? How does that affect their performance?

  • Flexibility

    Does it connect to moving parts? Will vibration be a factor? Stranded wire is more flexible than solid.

  • Durability

    Are the wires going to be pulled on or be routed through an enclosure? Should a grommet be used to prevent sharp edges cutting into the insulation? Is a strain relief needed?

  • Connectivity

    Does the wire need to be disconnected for servicing or convenience? Is the connection something a customer or end user will have access to?

  • Label / Color

    Is the wire color important? Does it need to follow a standard or published document?

All of these things may or may not be a factor in your project, and any of them can define what is "correct" for your application. (There are other things to consider which I've not listed, such as conductor material, weight, etc.)

Because you mentioned "12V 1.8A" I presume the first point is most important to you in this question. The ampacity is the ampere capacity of a particular conductor. There are lots of charts which provide these figures, as well as the math behind them. Generally the values are given for two cases:

  • Free air (the wire is not in a bundle and has the benefit of air cooling)
  • Bundle or enclosed (the wire is part of a bundle or otherwise not convection cooled)

Using the first linked chart, you can see that 24 gauge wire is sufficient for 1.8A in both free air (3.5A) and enclosed (2.1A). You have to derate these figures if the ambient temperature is significantly higher.

I frequently salvage wire from standard ethernet (UTP Cat5e) cabling for projects. Be careful though, Cat5/5e can use 26 gauge, too. Check the outer jacket for the wire gauge used.

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JYelton
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Current rating determines thickness, voltage rating determines clearance.

This link provides what looks to be EXTENSIVE coverage of clearance/creepage calculations: http://www.smps.us/pcbtracespacing.html

This link has a calculator that will help designing trace widths for different copper thicknesses: http://circuitcalculator.com/wordpress/?p=25/

Your copper thickness is most likely 1 ounce and let's say your highest ambient temperature is 40C with an acceptable rise of 10C. The calculator determines a 26.6 mil trace will result in 36 millivolts drop per inch.

HL-SDK
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    As far as wire guage, use copper resistivity calculations or a simple calculator like this: http://www.cirris.com/testing/resistance/wire.html and use the resistance to find power dissipated/voltage dropped. – HL-SDK Sep 17 '13 at 21:20