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Author Topic: 200 amps at 110 volts - what wire gauge is needed?  (Read 9337 times)
W8JI
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« Reply #15 on: October 05, 2012, 07:36:10 AM »

You'd be surprised at the people confused by wire size. I still remember some fool walking up to me at the Ameritron booth at Dayton, and telling me the AL1200 cord was too small to let enough current through, and if the cord was changed the power would go way up. He insisted he had an electronics degree. 

Excluding mechanical issues, there are two electrical reasons to pick a certain conductor size or material:

1.) current and permitted temperature rise

2.) percentage of voltage drop that is allowed

Think about this......

In my truck, I run a 2000 watt inverter through a six inch long section of #12 copper in a Teflon sleeve from the 12V batteries.
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G3RZP
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« Reply #16 on: October 05, 2012, 09:20:42 AM »

>2.) percentage of voltage drop that is allowed<

I think that is where people muddle up the conductor size and thus deduce (?) that the 'wire is too small to let the current through'. Possibly because of the old analogy of a water pipe?

Now what about true Litz wire with all those small conductors?
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K4RVN
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« Reply #17 on: October 05, 2012, 12:12:18 PM »

Since the voltage and amps were fixed at 110 and 200 amps respectively, only one variable remained and that is R. or wire size. While a 14 gage wire will carry 200 amps  what you get at the other end will not be the same as the supply end. Also Phil you are right and what I said was not correct. I did mention in my post about length, resistance and voltage drop and formulas. Hower the statement that voltage affects the ampacity was entirely incorrect as a general statement and I stand corrected.
The percentage of voltage drop in general would be 1/2 if the voltage supply were doubled for a given ampacity using the same wire.

Frank
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N4CR
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« Reply #18 on: October 05, 2012, 12:33:43 PM »

The percentage of voltage drop in general would be 1/2 if the voltage supply were doubled for a given ampacity using the same wire.

If you have a fixed resistance on the end of a pair of conductors and you double the voltage, then you double the current and the voltage dropped on the wire is increased linearly with the voltage increase. Thus the percentage of voltage drop is the same as you increase voltage when driving a fixed resistance load.

If you have a regulated power supply on the end of a pair of conductors and you double the voltage then you halve the current (approximately) and the voltage drop is an inverse proportion with the voltage increase.

Neither of those properties has anything to do with the ampacity of the wire other than making sure you don't catch the wire on fire.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
W8JI
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« Reply #19 on: October 05, 2012, 01:41:56 PM »

>2.) percentage of voltage drop that is allowed<

I think that is where people muddle up the conductor size and thus deduce (?) that the 'wire is too small to let the current through'. Possibly because of the old analogy of a water pipe?

Now what about true Litz wire with all those small conductors?

I think we try to use fancy words, and that confuses our communications. Ampacity is a word specially invented to mean ampere capacity dictated by NEC. We would all do a whole lot better not using it outside of application of NEC conductor size applications, because we might assume it means something it does not.

Conductors have thermal ratings caused by I^2 R heating, and they have voltage drop caused by current and resistance.
Nowhere in this does working voltage come into play.

If we allow 1 volt drop, it does not matter if the supply is 1 volt or 1 million volts, the wire size is the same for the same current and length.

If we allow a certain amount of heat for a given current, it is always the same no matter what the voltage.

When we mix this into a complex operation, like a certain % of regulation or heat at a certain load **power**, it is a different criteria. Now we change the current through the wire, and of COURSE the required size changes.

For example, if we allow 5% voltage drop and and a certain heat run 120 volts and it requires X mils cross sectional area of conductor for a certain conductor behavior, and then we run 240 volts at the same load POWER on the same wire, we now have half the current and half the voltage drop and twice the supply voltage, so regulation is FOUR times better. We also have half the current, and since heat is I^2 R then wire heat is FOUR times less for the same load power.

What messes us up is not working it as a problem for what we are really interested in, but CURRENT rating for a given voltage drop or heat clearly does not change with voltage.

 

 

 
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K4RVN
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« Reply #20 on: October 05, 2012, 05:39:17 PM »

Tom, good to read your comments. 110/ 120 now volts is usually in the realm of NEC and that's why I used ampacity. When I see
 voltage at 120 or 240 I associate that with the NEC tables for required wire size to maintain a decent voltage drop at a certain current. Of course, I don't really think any of this whole thread contributes a lot, just having fun here to see if I could read anything new. Don't be confusing me with the facts. LOL. I admitted I was wrong in my general statement.
I have never seen or had use for the power supply as described so would not classify that as worthy of using up my full memory bank. CB illegal stuf does not really turn me on. K8AXW had it right in my view, just a good laugh for this thread.

Frank
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N6AJR
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« Reply #21 on: October 19, 2012, 10:59:04 AM »

Yes, you have to remember that current, voltage and resistance  are all inter related. a 200 amp line running 12 v would look a lot like the fat starter cable on your car. The power needed to run a 200 amp power supply outputting 200 amps at 13.8 volts,  on 110 volts  still needs a couple of fat cables for the output but rule of thumb will put the input requirement on 110 volts is some where between 7 and 10 amps and half that on 220. this is assuming no loss in the power supply.  So I think # 12 or #14 gauge wire should be ok.
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G3RZP
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« Reply #22 on: October 20, 2012, 06:51:02 AM »

Small transformers run at about 1500 amps/sq. inch. For cables, you could push that to 2000Amps/sq. inch, as they wil get rid of heat more easily than a transformer. But you must also consider the resistance, which might demand a much heavier cable to minimise voltage drop, depending on length.
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