# Maximum current?

Discussion in 'General Electronics Discussion' started by XRZ, Oct 9, 2014.

1. ### XRZ

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Jul 30, 2014
A copper plate that is 0.5m wide, 2m long, and 3mm thick how much maximum current can it carry continuously without any damages? Basically how much power can it deliver continuously?

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Sep 5, 2009
3. ### Bluejets

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Oct 5, 2014
1/2 metre wide * 3mm = 1500 sq mm ........ probably close to 1000 amps conservatively based on the fact that 600mm2 will handle about 700 amps.
One thing about cable sizes and current rating though, it's not linear as size of conductor increases.
By the way, that's some copper plate..!!

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
I've always used the rule of thumb that 1 sq inch of copper can carry 1000A for the metric conversion, 1.6A per mm2 is close enough.

This doesn't take into account cooling based on the larger relative surface area of finer wire though so you'll find that thinner wire can carry significantly larger current that this rule of thumb would suggest..

5. ### Gryd3

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Jun 25, 2014
I always thought stranded wire carried less current than solid... Just read an article saying that the overall size of stranded wire is typically 8% larger than solid core, and the cross-sectional area of solid vs. stranded is the same. So what you said makes sense, but how much more current can typically be handled, and how does oxidization come into effect... (I've stripped automotive wiring that has had oxidized a few inched up into the insulation from the connector.)

6. ### Bluejets

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Oct 5, 2014
According to SAA wiring, and it was cross section area I was referring to, 1.5sq mm carries 15amp.
Although , as I also said, the value is not linear. 600 sq mm is around 700 amps.
If you have corrosion then it will be a setback as current flows in the first few microns of the surface of the conductor.
May well be said that cable could be made of steel with just a thin film of copper (earth stakes are actually made that way)
and I'm certain that cabling these days is not the same copper as was used say 20 years agne can compare old and new from older installations.
The overall size of "some" stranded cables is larger due to the air gaps between the conductors.
This is why they produce "compressed" cable as it is much smaller but the same cross section area, but a real mother to use.(very stiff)

7. ### Gryd3

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Jun 25, 2014
Forgive my ignorance on this one, but if current only flows on the surface of a conductor, than why do we see a cross-sectional area used to determine current flow limits instead of a perimeter?

I also understood ground stakes to be copper plated to help reduce/prevent corrosion.

8. ### Bluejets

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Oct 5, 2014
Yes, was a surprise to me also but apparently thats how it works.
Perhaps the copper on the stake is for corrosion protection but it doesn't work as rods rust away from the inside.
Also conductance tests are done to the copper cladding not the steel.

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Oct 5, 2014
10. ### Gryd3

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Jun 25, 2014
Thank you for the link, looks as though it is an issue for AC only, and does not apply to DC.

11. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Sorry, these are not things I can really answer. I believe Wikipedia has answers for the first of these.

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13. ### XRZ

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Jul 30, 2014
Yet, it's possible to have higher continuous current than the maximum, provided higher cooling. Air, water, or be a bit more fancy and use "liquid helium".

14. ### davennModerator

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Sep 5, 2009
Skin effect at AC mains freq 50/60Hz isn't really a problem
it only starts becoming significant once the freq gets up into the 10's of MHz to GHz