Wire sizes vs current capacity {split from Shops that install DC-DC charger}

[Gr8ful]

Just be careful of the cable you use as I watched a you tube where the guy used 2 gauge jumper cables. 2 gauge is the right size for 40 amp, 12 volt Copper cable. For alum cable it 2/0 which is considerable bigger than 2 gauge. I've noticed many jumper cable & audio cable are copper coated Aluminum cable. It looks like copper but is alum cable coated in copper. Just beware & verify. I would call a local, not a chain parts store, tell them what you need & they should direct you to someone that can help you as it's not rocket science. Thanks & good luck!

 

[Gr8ful]

I have a big wooden spool of 2/0 & one of #2 all copper with heavy coating. There's a theory I don't agree with. I go the next larger size anyway.

Does electricity travel on the surface of a wire?
"Thus the current flow in a wire is concentrated on the surface of the wire, as the current in the middle is repelled more than any other currents. Normally the effect is negligle, but design of high current wires is tricky. The electricity or current travels in the outer surface"

 

[INTJohn]

I have a big wooden spool of 2/0 & one of #2 all copper with heavy coating. There's a theory I don't agree with. I go the next larger size anyway.

Does electricity travel on the surface of a wire?
"Thus the current flow in a wire is concentrated on the surface of the wire, as the current in the middle is repelled more than any other currents. Normally the effect is negligle, but design of high current wires is tricky. The electricity or current travels in the outer surface"

^^^^Not entirely true at all…….
AC current experiences what’s known as “the skin effect” and travels along the conductor surface but DC does not and travels along the conductor bulk volume. Since vehicles are generally 12v DC, ummm……

https://byjus.com/question-answer/d...-flow-through-the-surface-of-a-conductor-or/#

The current flow in a DC circuit is caused by the movement of electrons, which are negatively charged particles. These electrons are found inside the wire, therefore the current flow is also inside the wire. In an AC circuit, the current flow is caused by the oscillation of the voltage. This oscillation causes the electrons to move back and forth, creating an alternating current.

In AC, Because the electrons are not actually moving through the wire, the current flow is found at the surface of the wire. Additionally, the skin effect in AC causes the current to concentrate at the surface of the conductor. It's also worth noting that the skin depth of a conductor is dependent on the properties of the material, the frequency of the current and the temperature of the conductor.

Just sayin…….
jonny boi

 

[rruff]

2 gauge is the right size for 40 amp, 12 volt Copper cable.

8 gauge pure copper is sufficient for 40A, but you may want to bump that up to 6 for reduced voltage drop if the run is towards the back of the van.

 

[abnorm]

^That's an AC wire table not a DC wire table........Try this one

 

[rruff]

^That's an AC wire table not a DC wire table........Try this one

That says the same thing. 8 gauge is adequate for 40A.

 

[Gr8ful]

12v DC takes a lot bigger wire size. 12v, 20' copper needs @ #2 wire. I use this calc https://www.omnicalculator.com/physics/dc-wire-size

 

[tx2sturgis]

Fun factoid department: 'skin effect' is much more pronounced at Radio Frequencies, RF, (which is also AC) than at audio frequencies.

60 Hz AC happens to be an audio frequency, although we typically don't consider it as being 'audio'.

But once we get into RF in the megahertz and gigahertz ranges, skin effect is such a factor that the conductors can behave completely differently than if they were carrying DC or 'audio' AC.

Off topic detour....my bad!

 

[rruff]

12v DC takes a lot bigger wire size. 12v, 20' copper needs @ #2 wire. I use this calc https://www.omnicalculator.com/physics/dc-wire-size

Lot bigger wire size than what?

You have two things to consider 1) Wire's ability to carry current without overheating 2) Desired voltage drop

If you have 40A current, then 8 gauge is sufficient. If you have a 20 ft wire run, 8 gauge, and 40A, then you'll have a 8.3% voltage drop and power loss. The DC-DC controller will have no problem with that. If you bump that up to 4 gauge it will be a 3.3%. It's up to you if the lower loss is worth the bigger wire.

 

[bullfrog !]

When doing solar or 12 volt DC in general shorter distances are better and bigger is usually better if you can deal with routing larger wire. 20’ of 8 gauge will be noticed in winter when trying to charge batteries at a reduced rate. I try to limit my runs to less than half that and use 6 gauge at a minimum. There is a point of diminishing returns but undercharging batteries get expensive as well at least on the older lead acid batteries.

 

[LargeMarge]

I j buy stranded copper wire from
Marine sources whenever possible. But as I was...

.
Manufacturers can 'tin' marine wire and cable to exclude oxygen and reduce corrosion.
.
[as this thread has concerns wiring, and as the Originator has concerns about skills, I think my contribution has appropriate information... as I usually do]
[As you were.]

 

[LargeMarge]

... solar or 12 volt DC in general shorter distances are better and bigger is usually better if you can deal with routing larger wire. 20’ of 8 gauge...

.
Example:
A couple weeks ago, I moved my starting batteries from the side of the frame to between the frame-rails and above the rear axle.
Stock battery cables were 2/0 (two-ought).
I fabricated and ran new 4/0 (four-ought) welding-cables... about a half-inch across and close to a pound a foot.
.
The stock run was about 8'/2.3m.
The new run approaches double that.
.
Amp-meter showed a ten-percent (10%) loss by duplicating the factory single ground, so I added a second ground-cable from the bank to increase capacity.
This reduces line-loss to around three percent (3%), and I can live with that.
.
.
An aside:
I think 8-gauge is woefully inadequate for 40-amp DC at any length.
I also think factory-installed massively-excessive cubic-displacement is significantly more fun.

 

[Gr8ful]

The CORRECT charts & calculators prove 8-gauge is woefully inadequate for 40-amp 12VDC at any length.

 

[Gr8ful]

Too Bad for the OP the moderators deleted the Correct Charts & Calcs but leave in the Wrong ones. ): Weirld place!

 

[rruff]

When doing solar or 12 volt DC in general shorter distances are better and bigger is usually better if you can deal with routing larger wire. 20’ of 8 gauge will be noticed in winter when trying to charge batteries at a reduced rate. I try to limit my runs to less than half that and use 6 gauge at a minimum. There is a point of diminishing returns but undercharging batteries get expensive as well at least on the older lead acid batteries.

The run is from the battery to charge controller. The battery will not be undercharged.

 

[rruff]

The CORRECT charts & calculators prove 8-gauge is woefully inadequate for 40-amp 12VDC at any length.

The calculator you linked also says that 8 gauge is adequate for 40A. There is 100% agreement on this.

What do you think was deleted?

 

[Gr8ful]

Sorry but you're WRONG! I posted 3 charts & 3 Calcs that were deleted. This was my 1st Calc before you 2 posted AC 120V charts https://www.omnicalculator.com/physics/dc-wire-size Put in 40 amps, 12 volts, 20' copper & you'll get the same answer as below
Recommended wire gauge:
2
AWG

 

[Gr8ful]

I'll PROVE 8ga is for 120vac, Not 12vdc. Then admit you're Wrong. Just google 120v ac wire size chart & this comes up before the charts


The size of wire needed for 120-volt AC depends on the amperage required:

• 16-gauge: 13 amps
• 12-gauge: 20 amps
• 10-gauge: 30 amps
• 8-gauge: 40 amps
• 6-gauge: 55 amps
• 4-gauge: 70 amps
• 3-gauge: 85 amps
• 2-gauge: 95 amps
  
  
  
  

 

[Gr8ful]

Aborn's chart IS correct as NO ONE uses a 10% loss factor unless you want a fire. Why do you have such a problem making a mistake? It's how normal people learn & grow.

 

[rruff]

Aborn's chart IS correct as NO ONE uses a 10% loss factor unless you want a fire. Why do you have such a problem making a mistake? It's how normal people learn & grow.

Wrong on all counts again...

Go back and read the post where I did the calculations on loss. Overheating and voltage drop (loss) are different parameters. 8 gauge is adequate for 40A DC. It won't start a fire. The size requirement to prevent overheating is independent of wire length, but the voltage drop obviously is not.

The calculator you linked also says 8 gauge is adequate for 40A. The reason it recommend 2 gauge is because you put in 3% loss and 20 ft.