DC wire types

[pvstoy]

Things I learned a long time ago for wiring DC voltage wiring. Current is carried on the surface of the wire diameter. The bigger the diameter the more current can be carried. So bigger wires carry more current efficiently and has less loss over longer distances.

So assuming what I learned was accurate, I have been using fine strand welding wire. It has a incredible amount of surface area to carry current and wire is flexible. More expensive is tinned wire. Welders use this wire for long extensions from welders to project with minimal loss and wires don't heat up. I have a set of old jumper cables that are fine wire type ( I'm sure they all are for the flexibility).

So question, If you used #4 welding wire is it equivalent to braided #4 wire? #4 braided wire has a larger diameter. Do they both have the same amount of diameter surface area?

There has been lots of talk about wire gauge sizes and losses over distances but not much on what wire types. I'm inclined to keep using wire with "Fine" wire for higher Amp runs unless somebody can shed more light on me.

Cheers.

 

[MarkBC]

Hmmm....never heard that before -- current being carried just on the surface of a wire. It's been my understanding that the bigger the diameter increases current capacity because you're increasing the cross-sectional area of the wire -- not the circumference of the wire.
As indicated here...and here.

 

[cwdtmmrs]

I heard it decades ago as well. Never sure to believe it or not.

 

[takesiteasy]

According to my good friend Google, this is known as the "skin effect" applicable to alternating current. The effect increases at increasing frequencies.

DC current flows uniformly through the cross section of the wire.

https://en.wikipedia.org/wiki/Skin_effect

 

[PaulT]

DC current is distributed through the wire.
AC current is pushed towards the outside of the wire with higher frequencies resulting in current being carried more to the surface.

Look at skin effect discussion here: http://edisontechcenter.org/wires.html
Wiki has some articles on the skin effect also.

Paul

 

[Wandering Sagebrush]

From my AC theory classes almost 50 years ago, skin effect is very real, but is really not an issue for low frequency applications. Multi strand wire is the norm for both AC and DC aircraft applications. The military aircraft I worked on were all 400 hz produced by inverters.

 

[ntsqd]

I've run into the same thing in my various employments, skin effect becomes more prevalent as the frequency increases. High enough frequency no longer even uses a wire or cable, it uses a corrugated metal tube called a 'wave guide'.

When you say "braided wire" are you referring to flat braided cable? If so my understanding is that gauge for gauge they conduct current about the same, but flat braided is more preferable for ground bonding. I never did get a good sense of why, but experience has shown this to be correct.

 

[pvstoy]

Wow all good stuff. Never too old to learn stuff and kill the miss learned information from long ago. Skin effect on AC only not DC flow. Thanks for all the links.

Thom I miss typed and should have said Thick copper strands vers Thin copper strands. I did find some Google information that helped explain the differences. Below is the information copied from the page. http://blog.delcity.net/whats-the-difference-between-battery-cable-and-welding-cable

Applications
If you just need a simple connection between a battery and its starter, battery cable is the ideal solution. For applications with no sharp curves or those that have a direct shot to the power source, battery cable is the most efficient option. The copper strands within battery cable are thicker and not as tightly compacted in the PVC sleeving, making battery cable less flexible but more cost-effective option when the benefits of welding cable are not necessary. Due to the thicker copper strands, there are fewer strands in battery cable when compared to welding cable of the same gauge size. This difference limits battery cable to applications or projects that need no more than 60V power.

When a lot of bends are required to complete the wiring of an application, welding cable is often preferred due to its flexibility. The flexibility of welding cable is a result of its construction using finer strands of copper and EPDM insulation. Because of the finer copper strands, the amount of copper per foot is greater in welding cable than battery cable, which allows welding cable to handle higher voltage applications. Welding cable got its name because it was initially used for welding purposes, since often times welding machines require mobility and battery cable is not as mobile due to its inability to move, unroll, and bend. That said, welding cable is a better choice for those applications where the cable usability is important.

The Elements
Battery cable's smooth thermoplastic polyvinyl chloride (PVC) jacket protects against cracking, abrasion, weather, oil, and acids. Battery cable meets the UL-558 and UL-553 flame resistant standards.
Similarly, welding cable resists grease, oil, and water, as well as protecting against cuts and tears. However, welding cable is also flame resistant, but meets the UL-1581 standards. This UL rating gives it an edge on battery cable when it comes to protection from the elements.

Environment
When simple connection and protection is needed on your application or project, battery cable is the best choice to keep your electrical connections running. However, in cold weather battery cable becomes very stiff and difficult to work with.
On the other hand, welding cable is ideal for installations with exposure to colder weather because of its construction with thinner stranding which allows increased flexibility and usability. However, both perform similarly in cold conditions.

Battery cable provides a budget friendly, cost-effective solution to your battery projects and applications that need no special enhancements while providing excellent protection and connection. However, if usability is a top priority, welding cable is the way to go.

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[klahanie]

You don't want thick copper strands wire anyway (like a #4x7 strand construction THHN) because more strands will be better not only for working in small spaces but also for vibration which can cause breaks at connections. SAE wire will be multi strand, used by auto makers and RV mfgrs ... well never mind...

Flipping around online I saw that SAE wire like the J1127 standard used for battery cables will typically have a smaller internal cross section of copper, sometimes measured as CM for circular mil area, than AWG wire (which I think welding wire would be classified under). And therefore can carry less current. So a #4 is not the the same as a #4, you'd want to compare the cross section (see link below for CM difference but doesn't show difference of AMP rating)

Yes the insulation type will affect flexibility but also oil, heat, abrasion and fire resistance. Marine wire under ABYC requirements will have a self extinguishing insulating cover not just flame resistant. Also tinned I believe for corrosion resistance.

I'd use a few online wire calculators that uses 12VDC (fwiw was happy with this supplier's product and price)

http://www.genuinedealz.com/voltage-drop-calculator

 

[Squatch]

This is the wire I used on my camper. Very good quality and price.
Flat Duplex DC Marine Wire

Also a good source for fuses and circuit breakers.

I used Anderson connectors where I needed to plug and unplug things.
Got most of that here. along with crimp tools.
Anderson Power Products SB50 SB Series 50 Amp Connector Kit

We also have a west marine locally so they were good fo the larger battery cable ring terminals and small parts.

I prefer marine grade products. Most are well made and corrosion resistant. The wire insulation is made to lay in bilge water with fuel in it if it has too. Tough stuff".

 

[ntsqd]

Some time ago I found the attached pdf on welding cable specs. Maybe it's still useful?

After West Marine closed my local store I recently bought from bestboatwire for the first time, and will do so again. It isn't Ancor Marine wire, but it looks to be just as good. Time will tell if it is.

 

[Squatch]

I have both brands and really can't tell any difference other than price.

 

[cwdtmmrs]

Ditto

cwd