12v vs 110v copper

[mjoekingz28]

Just wondering why in 12v you have many small strands of soft copper. In the house there is one wire that is very reluctant to bend (it worries me it will break when I change out the power outlets).


Just wondering why this is? There is probably no short answer. Also it is weird that in a car to pull 1000 watts you need 4 gauge or better, but in AC a little 12 or 16 gauge is more than sufficient.

 

[zrxkawboy]

Stranded wire is used in automotive applications because it holds up to vibration better.

12VDC x 100A = 1200W
120VAC x 10A = 1200W

Therefore, even though they're both 1200W, the 12V wire is carrying 10x the current.

 

[Chris142]

Cars use stranded wire because it is better to use when vibrations are present.

12vDC and 120vAC are much different. The higher the voltage the less amps a component draws.

A product that uses 1000w with 12v will take 83.3 Amps. Bump the voltage to 14v and it only takes 71.4 Amps.

1000w when used with 120V only uses 8.3A.

 

[MolaKule]

Many small strands of soft copper are more reliable in an automobive application. You have more vibration and fatigue in automotive wiring, not so in house wiring.

It has to do with voltage and the amperage required as per Ohms Law where Power = Current(I) X Voltage(V), and V = I X Resistance(R). If you have a higher voltage source, you can have more power with a smaller current.

House wiring: Maximum Power = 1800 Watts for a 15 Amp circuit at 120Volts. 14 guage solid is the norm.

Car wiring: Power = 1800 Watts for a starter with 150Amps at 12Volts. Stranded 6 guage or lower is the norm.

The resistance in a wire also varies with diameter, I.E., the lower the guage (larger diameter), the lower the resistance.

The voltage "Drop" in a wire is across the resistance of the wire. The higher the resistance, the more voltage that is dopped across the total length of wre.

Since you are carrying more amperage for a starter circuit (at the lower voltage), you need a lower resistance, larger diameter, small guage wire in order to reduce the voltage drop to the starter. Otherwise, there would not be enough voltage (and hence, not enough sufficient power) to turn the starter.

 

[CarbonSteel]

Stranded wire also carries more current than its same sized solid counterpart. This is because stranded wire is composed of a bundle wires to make a larger conductor [http://en.wikipedia.org/wiki/Wire].

Industrial/commercial applications also use stranded wire for electrical requirements versus solid.

 

[PandaBear]

Originally Posted By: 2010_FX4
Stranded wire also carries more current than its same sized solid counterpart.


I don't think it is true in DC or low frequency, the cross section of the conductor matters but not the surface area. It has more to do with mechanical property of the application than electrical for power transmission.

In high frequency, they will be different due to skin effect.

 

[L_Sludger]

Originally Posted By: PandaBear
Originally Posted By: 2010_FX4
Stranded wire also carries more current than its same sized solid counterpart.


I don't think it is true in DC or low frequency, the cross section of the conductor matters but not the surface area. It has more to do with mechanical property of the application than electrical for power transmission.

In high frequency, they will be different due to skin effect.
Skin effect makes me wonder why they don't use more hollow or non-conductive cored wires for AC purposes to save money and weight on AC installations.

 

[Al]

Imagine trying to use solid wire in wiring harnesses.

Its for flexibility

 

[SteveSRT8]

Flexibility AND redundancy. Combine that with more current capacity and you choose stranded every time.

 

[Pop_Rivit]

Originally Posted By: mjoekingz28
(it worries me it will break when I change out the power outlets).


Unless there's a problem with it you can bend house wiring without fear of it breaking. I suppose it's possible to bend it back and forth enough to break, but having wired several houses I've never had solid copper wiring break with normal usage.

Have you ever watched an electrician work? If it can withstand the abuse of being pushed, pulled, stripped, bent, twisted and turned it most certainly can withstand you replacing an outlet. It's pretty tough stuff.

 

[tom slick]

Solid wire is used in residential because it's less expensive than stranded and the majority of terminations (switches, receptacles, etc) are easier and faster to wire with solid wire. NM cable ("romex") is the norm for residential and its stiffness is an asset when running the wire all over a house. In commercial/industrial you'll see more stranded wire because its flexibility makes it easier to pull through conduit.

 

[JHZR2]

Originally Posted By: L_Sludger
Skin effect makes me wonder why they don't use more hollow or non-conductive cored wires for AC purposes to save money and weight on AC installations.


Buss pipe is used in certain applications now.

 

[OilProfessor]

Originally Posted By: MolaKule
Many small strands of soft copper are more reliable in an automobive application. You have more vibration and fatigue in automotive wiring, not so in house wiring.

It has to do with voltage and the amperage required as per Ohms Law where Power = Current(I) X Voltage(V), and V = I X Resistance(R). If you have a higher voltage source, you can have more power with a smaller current.

House wiring: Maximum Power = 1800 Watts for a 15 Amp circuit at 120Volts. 14 guage solid is the norm.

Car wiring: Power = 1800 Watts for a starter with 150Amps at 12Volts. Stranded 6 guage or lower is the norm.

The resistance in a wire also varies with diameter, I.E., the lower the guage (larger diameter), the lower the resistance.

The voltage "Drop" in a wire is across the resistance of the wire. The higher the resistance, the more voltage that is dopped across the total length of wre.

Since you are carrying more amperage for a starter circuit (at the lower voltage), you need a lower resistance, larger diameter, small guage wire in order to reduce the voltage drop to the starter. Otherwise, there would not be enough voltage (and hence, not enough sufficient power) to turn the starter.







The Professor agrees with everything Molecule stated above. There should be no more questions on this topic.

 

[MolaKule]

Quote:
Industrial/commercial applications also use stranded wire for electrical requirements versus solid.


Yes, but mostly where there is vibration such as fans, blowers, etc., or the possibility of fatigue.

Termination is a consideration as well in electrical wiring. Simple terminations can be made with solid wire, whereas special crimp or solder terminations are needed with stranded wire.

 

[jaj]

The choice of solid vs stranded wire is based on the physical properties of copper. If you bend a copper rod (like a wire) through a bend with a radius of 3 or 4 times the diameter of the rod once, the stress causes the formation of crystaline structures at the site of the bend. If you bend it that way a dozen times, the wire will fracture along the crystaline boundaries. This is work-hardening and fatigue.

However, if you bend a copper wire through a bend with a radius of 1000 times the diameter of the wire, there is very little stress on the wire, and it takes tens or hundreds of thousands of bending actions to form crystals.

So, in your house, where most bends aren't sharp and the wire doesn't have to flex from day to day, with the exception of where the wire wraps around a screw for a connection, there's no place where the wire can work harden and break. And, wire with one strand is cheaper than wire with many.

For applications where the wire has to bend, a bundle of thin strands allows the wire to flex through some fairly steep angles without work hardening. The flex radius is many times the diameter of the individual wires even though it might only be 5 to 10 times the diameter of the finished bundle.

So, stranded wire is used where any flexing is required, and solid is used where flexing is not an issue.

As for surface effects in AC, I worked it out once and it's immeasurably small at 60Hz. It's simply not a factor. What is a factor though is that, where practical, you make a buss structure that has the most surface area to improve heat removal. You can use a smaller cross section that way, provided it still passes the thermal rise tests that the product needs to pass for UL or CSA approval.

 

[brianl703]

Originally Posted By: L_Sludger
Skin effect makes me wonder why they don't use more hollow or non-conductive cored wires for AC purposes to save money and weight on AC installations.


There's not much skin effect at 60Hz...

 

[brianl703]

Originally Posted By: MolaKule

Termination is a consideration as well in electrical wiring. Simple terminations can be made with solid wire, whereas special crimp or solder terminations are needed with stranded wire.


Commercial receptacles with the "side wire" clamp terminals are rated for either stranded or solid wire. I am fairly certain that most circuit breakers are as well.