curious about wire gauge ampacity and multistranding

[sdowney717]

if you have 1 12 gauge solid copper rated for 20 amps.
What if you combine 3 12 gauge solid copper twisted together, what is it equivalent 10 gauge?
Or would it take 4, 12 gauge copper wire to make a single 8 gauge wire equivalence.

(think of it similar to multistranded copper wire.)

 

[sberry]

First, the numbers are not accurate but second and this is a big one,,, this is a no-no in real world application, with wires this size it is a code violation and then some.

 

[sdowney717]

Here is a discussion, you can do it with large cable, 1/0
http://www.plctalk.net/qanda/showthread.php?t=45042
yes I know it is a code violation. I was just wondering.

 

[sdowney717]

I have a bunch of 12 gauge laying around and was wondering about stripping it and twisting it into a bundle for 12 volt starting motor for an engine.
I would run it in small plastic pipe. Yeah its all free stuff.

actually it is a battery bank relocation project I was thinking of. I still have fine multistrand
going to the starters at the battery selector switch
Run would be about 10 feet.

The other idea was a copper coated ground rod in a plastic pipe.

 

[supertooljunkie]

You might find the answers in the NEC code book. Get some heat shrink tubing for extra protection.
The electrons flow around the OD of the wire strand not through the core. That is why stranded wire is a better conductor.

 

[sdowney717]

since it flows on the outside what about a copper pipe as a conductor?
I have a bunch of 1/2 inch copper pipe laying around going to waste.
Sort of think that might get hot carrying starting current.

 

[sdowney717]

I dont really like the battery location right now. It gets in the way when working on the engines, it is more risky I think to have the hydrogen gases in the cabin area of the boat.
Advantage is the wire run is short. Its been like this from factory new in 1970

 

[sdowney717]

an advantage would be moving it under the aft lazarette cockpit space close to the generator. It would still be out of the weather and it would be away from the living space. Next to the 70 gallon water tank is a nice open space that can easily take the batteries. It originally had 4 6 volt batts, but I changed to two 12 volt. This new space could still handle 4 6 volt batteries if someone wished.
The wire is free and copper pipe is free, it is just my ample time I have to work on the project.

ground rods I think would work, but cost money plus need some kind of clamp.
For terminal ends on copper wire bundles, I take a piece of tight fit copper pipe slide it on and hit it down flat with a sledge hammer, drill a hole, it works great.

 

[mrb]

electricity flows through the copper, not just on the outside. That is called skin effect when its on the outside and is only applicable at high frequencies.

 

[sdowney717]

how much ampacity can those copper ground rods handle?
They are copper coated, with steel inside.

 

[rabidsquirrel]

Dude, just do it the right way. You're creating a recipe for disaster or a Darwin award. Not to mention it'll probably look like syphilitic goats chewed it up and shat it out.

http://www.google.com/products/cata...og_result&ct=result&resnum=3&ved=0CCkQ8wIwAg#

 

[sdowney717]

that is an interesting product, BUT remember, this is a boat, the engines are large and take a lot of current to get them to spin and I dont know if their wire is big enough.

The present battery cable is around 1/2 " thick worth of copper, not counting the insulation, maybe more

I will need 3 wires, 2 banks for positive and one for negative.

 

[rabidsquirrel]

that is an interesting product, BUT remember, this is a boat, the engines are large and take a lot of current to get them to spin and I dont know if their wire is big enough.

The present battery cable is around 5/8 " thick worth of copper

Sounds like it's welding cable. Super fine strands? You're still better and safer buying the right material, especially for only 10 feet.

 

[sdowney717]

yeah it is thick wire like welding cable. I imagine that would be very expensive.
It is something I have put up with the batteries in that spot and it has not killed me yet.
So not willing to spend a large sum, I am looking at what I have laying around that might work.

 

[sdowney717]

I bet OOOO (4 ought) service feeders might work, but that will cost me.
I called ECK and was looking for something bigger mcm next size up but it gets pricey.
Worst thing to do would be to spend money and you find out too much voltage drop when it cranks.

Plus those cables are mostly aluminum and if copper than must be twice as high as high.
Aluminum wire on boat in salt water not good, maybe if free worth a try, but dont have it laying around now.

 

[Aceman]

This is crazy. You can't determine what size wire you need without knowing how much current you need to pass through it. Then, your trying to cobble it together with ****** parts. What a disaster waiting to happen.....

Put the fire dept on speed dial.....

 

[sdowney717]

well, yeah, that is why I am very reluctant to spend any money on the idea.
I am pretty sure I could buy cable and make it work ok.
The failure mode here is the engines wont crank fast enough or at all and the wires would get too hot. But you will know immediately when you got to start the engines if it is not going to work.

 

[sdowney717]

I figure if it was designed to handle a thousand amps, then it would be more than enough.
http://www.peachparts.com/shopforum/archive/index.php/t-221177.html

typically these engines draw not more than 500 amps.

 

[mrb]

the right cable isnt going to be THAT expensive....4/0 in either welding cable or type SC is going to be between $4 and $5 a foot

 

[sdowney717]

http://www.skycraftsurplus.com/thhnbuildingwire250mcm.aspx

Ok, maybe not too bad. I originally recall looking at 250 mcm which I think is one up from 4/0
still, I got a very large amount of 12 gauge romex here. I had some in the basement leftover couple hundred feet and my friend gave me a couple hundred feet after we did his whole house. Just was thinking of burning off the insulation and it using for something like this making my own wire bundle. I am not a trade electrician, but do some occasional wiring., so its not like it will likely be used for wiring.

not less than 100 feet = $376. I guess I wont be buying from them!

 

[sdowney717]

found the wire size for various wire gauges here
4/0 is slightly less than 1/2 inch across

If I moved the batts, I would need 3 wires at least 10 feet long, so 30 feet of wire.

I went looking thru garage and did find 2 old boat battery cables about that long. They look like welding cable wire. They are not 4/0, look more like 2/0 or 3/0 What I will do someday is take them out there and see if they can crank the engines.
I have a lot of junk collected from a lot of years

http://www.allaboutcircuits.com/vol_1/chpt_12/2.html
WIRE TABLE FOR SOLID, ROUND COPPER CONDUCTORS

Size Diameter Cross-sectional area Weight
AWG inches cir. mils sq. inches lb/1000 ft
===============================================================
4/0 -------- 0.4600 ------- 211,600 ------ 0.1662 ------ 640.5
3/0 -------- 0.4096 ------- 167,800 ------ 0.1318 ------ 507.9
2/0 -------- 0.3648 ------- 133,100 ------ 0.1045 ------ 402.8
1/0 -------- 0.3249 ------- 105,500 ----- 0.08289 ------ 319.5
1 -------- 0.2893 ------- 83,690 ------ 0.06573 ------ 253.5

 

[mrb]

http://www.skycraftsurplus.com/thhnbuildingwire250mcm.aspx

Ok, maybe not too bad. I originally recall looking at 250 mcm which I think is one up from 4/0
still, I got a very large amount of 12 gauge romex here. I had some in the basement leftover couple hundred feet and my friend gave me a couple hundred feet after we did his whole house. Just was thinking of burning off the insulation and it using for something like this making my own wire bundle. I am not a trade electrician, but do some occasional wiring., so its not like it will likely be used for wiring.

not less than 100 feet = $376. I guess I wont be buying from them!

you do not want 250mcm THWN or building wire. You wont be able to bend it. You need welding cable, type SC, type W, DLO

 

[Aceman]

you do not want 250mcm THWN or building wire. You wont be able to bend it. You need welding cable, type SC, type W, DLO

The guy was about to use a copper clad steel ground rod, I really don't think he cares if it's even wire. Let alone what type it is.

Honestly, I think all the advice he's been given has went in one ear and out the other....

He's going to do what he feels like regardless of it being right or not.

 

[sdowney717]

Look what someone tossed to the curb

I could put my home made copper wire bundle inside that 1" liquidtight.
Even though I have a lot of wire, I really dont know if I have enough 12 gauge wire around to try it.

 

[sdowney717]

Label says this

 

[sberry]

The code stuff doesnt apply for cranking engines, this whole thread started on left foot.

 

[Aceman]

The code stuff doesnt apply for cranking engines, this whole thread started on left foot.

There wasn't one post that mentioned he needed to do it to code.

That still doesn't mean twisting a bunch of #12's together is okay IMO.

 

[Norcal]

There wasn't one post that mentioned he needed to do it to code.

That still doesn't mean twisting a bunch of #12's together is okay IMO.

Agreed & well said, do it right or don't do it at all. The welding cable written about in earlier posts is a good idea, just do not use connectors made for building wiring for it as they are not designed for fine stranded cable that would be likely to pull out from a connector not made for the purpose.

 

[sberry]

There wasn't one post that mentioned he needed to do it to code.

That still doesn't mean twisting a bunch of #12's together is okay IMO.

No one said it was a good idea but the start of this thread was incomplete at best, nice to have the hindsight though isn't it? Not to be mean but I will agree this certainly sounds like a cobbled mess, if a guy is a first class scrounger he should be able to come up with something better than a couple of these ideas.