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Thick wire vs thin wire

by coffee-3000
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coffee-3000
#1
Jan9-09, 07:24 AM
P: 5
If a thick wire has less resistence which allows more current to flow, why not always use a thick wire rather than a thin wire ? For example, if you have small circut with a 1.5 volt battery use to light a 1.2 volt bulb, why not use a 12 gauge wire (i.e. thick wire) rather than a 22 gauge thin wire ? Don't you always want to cut down on the resistence ?
Or is the current so small that neither wire will provide resistence ?
Just curious.
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Pumblechook
#2
Jan9-09, 07:37 AM
P: 359
Current is so small such that the power loss is neglible.

Power loss (Watts) = Current (Amps) Squared x total resistance of the wiring (Ohms)

Clearly the length of cable run comes into it.
coffee-3000
#3
Jan9-09, 08:02 AM
P: 5
I see. You actually lose some power when using the thinner wire but it isn't enough to matter. I guess it is not enough of a power loss to dim a bulb.
Thanks for your response Pumblechook .

Pumblechook
#4
Jan9-09, 08:16 AM
P: 359
Thick wire vs thin wire

There is also the question of volt-drop and wires getting warm.

If a wire to a 2kW (230v) heater is dropping 3 volts in 230 so that the heater is now down to 1950 Watts (due to the lower voltage) you could say that is neglible and the incoming mains varies anyway. But the wires might be quite warm and present a hazard or at least eventually make the insulation brittle.

You can lose 3 volts in 230 with little effect but you wouldn't want to lose 3 volts in a 12 volt system. 230 to 227 is nothing but 12 to 9 is a much bigger proportional drop.
stewartcs
#5
Jan9-09, 08:17 AM
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Quote Quote by coffee-3000 View Post
If a thick wire has less resistence which allows more current to flow, why not always use a thick wire rather than a thin wire ? For example, if you have small circut with a 1.5 volt battery use to light a 1.2 volt bulb, why not use a 12 gauge wire (i.e. thick wire) rather than a 22 gauge thin wire ? Don't you always want to cut down on the resistence ?
Or is the current so small that neither wire will provide resistence ?
Just curious.
Cost is an important factor too. The more material used the more it costs. Engineers typically design things to be as efficient, economic, and practical as possible.

CS
coffee-3000
#6
Jan9-09, 08:51 AM
P: 5
That sounds good. I will switch from a thin to a thicker wire if I encounter an unexpectable voltage drop. It also sounds like thicker wire cost more than thin wire. So if I need a lot of wire, I'll use the thinner wire if it does the job (without loss of voltage and without causing the wire to get too hot). But I can also infer from this discussion that both the thinner and thicker wires will do the job. So it is acceptable to use the thicker 12 gauge wire if I'm helping my son create a small low voltage circut for his science project ( and the 12 gauge wire is the only wire I have available).

Joe
Mapes
#7
Jan9-09, 09:19 AM
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You might find it interesting to look at a table of resistance vs. wire gauge (example). This will quantify things and probably alleviate your worries. It looks like 12 gauge wire has a resistance of about a milliohm per foot. If you're passing an amp through several feet, the voltage drop would be in the millivolts.
yungman
#8
Jan9-09, 11:21 AM
P: 3,883
You can over kill by using as big a wire as you want. You just have to deal with the inconvienence of the stiff wire, weight and all.....Also funny looking!!!
f95toli
#9
Jan9-09, 11:47 AM
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What is written above is correct for DC.
However, at higher frequencies the concept of skin depth becomes important; most of the current will flow in a thin "shell" with a thickness that is inversely proportional to the frequency; for copper the skin depth is several mm at 1 kHz but only about 70 um at 1 MHz. Hence, at higher frequencies there is no real point in using very thick wires (and in ex. coaxial cables most of the energy is actually transmitted in the dilelectric; not in the conductor).

btw, the skin depth is also the reason why there is no real electrical reason for using VERY thick copper wire in e.g. power applications, anything above about 1 cm is a waste of metal for 50/60 Hz applications.
yungman
#10
Jan9-09, 12:31 PM
P: 3,883
Thicker wire have more surface area.

Seriously, This is for his son's project, I doubted skin effect will come into play!!!
Danger
#11
Jan9-09, 01:17 PM
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You alluded to another issue, Yungman, which deserves a readdress. A thicker wire is much less flexible, and therefore harder to work with.
yungman
#12
Jan9-09, 02:55 PM
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Quote Quote by Danger View Post
You alluded to another issue, Yungman, which deserves a readdress. A thicker wire is much less flexible, and therefore harder to work with.
I made light on the wire because this is for the son's project. Actually it is a lot more involved. I actually designed a connecting cable for the Land Warrior soulder carry on system. The cable contain pair of Firewire, USB, a RF link and power. The first version was so thick it would be hard for soulder to move around with this feeding to helmet, to the gun sight and to the belt. I have to go through the loss of all the links to try to get the smallest custom cable I could use. We were sub contractor, I don't know how it end up since I left 5 years ago.

All the dielectric loss, skin effect loss and last but not the least can it survive when the soulder use it to choke the enemy!!!.....Just joking
Proton Soup
#13
Jan9-09, 06:09 PM
P: 1,070
Quote Quote by Danger View Post
You alluded to another issue, Yungman, which deserves a readdress. A thicker wire is much less flexible, and therefore harder to work with.
yup, and if you're pulling cable in conduit, that sucks. even worse, oversized wire leads to oversized conduit, which runs up costs even more.
Redbelly98
#14
Jan9-09, 06:32 PM
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For many low-voltage home hobby circuits, 22 AWG wire is a convenient size. In fact solid 22 AWG wire is perfect for using with the breadboards commonly used for circuit prototyping.

Not sure just what the current limit is for 22 AWG, but I think it will pass 1 Amp easily.

12 Gauge would be quite cumbersome if for example you're soldering it to 1/2 Watt resistors. Plus you'll need a rather powerful soldering iron to heat up wire that thick.
yungman
#15
Jan9-09, 06:51 PM
P: 3,883
Quote Quote by Redbelly98 View Post
For many low-voltage home hobby circuits, 22 AWG wire is a convenient size. In fact solid 22 AWG wire is perfect for using with the breadboards commonly used for circuit prototyping.

Not sure just what the current limit is for 22 AWG, but I think it will pass 1 Amp easily.

12 Gauge would be quite cumbersome if for example you're soldering it to 1/2 Watt resistors. Plus you'll need a rather powerful soldering iron to heat up wire that thick.
Bend the wire, you break the resistor!!! Try stick it onto the breadboard!!!
Redbelly98
#16
Jan9-09, 07:48 PM
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Quote Quote by yungman View Post
Bend the wire, you break the resistor!!! Try stick it onto the breadboard!!!
Could you explain a little better what you are saying? Bend which wire? Stick what (the resistor or a wire?) onto the breadboard?
yungman
#17
Jan9-09, 08:04 PM
P: 3,883
Quote Quote by Redbelly98 View Post
Could you explain a little better what you are saying? Bend which wire? Stick what (the resistor or a wire?) onto the breadboard?
Don't take me too serious!!!

You solder the resistor between two 12 gauge wire, try to bend it, the resistor is going to give!!

The proto breadboard are ones that have small holes that you stick wire into the hole and the spring inside will hold the wire to make a connection. But the holes are small, only for 22 gauge solid wire can fit.

We pretty beat this post to death already, I am just having fun!!! Friday night and I am getting silly!!!
Proton Soup
#18
Jan9-09, 09:11 PM
P: 1,070
well, yeah, you can damage components bending the leads. but by holding the lead firmly with pliers or using a lead-bending tool, you can safely bend the leads without damage.


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