6 AWG vs 4 AWG

[themiller]

Which has a higher current carrying capacity - a 3’ run of copper 4 gauge or a 6” run of aluminum 6 gauge?

I think I know, just trying to confirm from an expert.

Thanks!

 

[Bert_]

Current capacity has nothing to do with distance. Distance will affect voltage drop but doesn't need to be considered at that length.

 

[mike93lx]

Edit, had them backwards.

6 cu = 4 AL, not the other way around

 

[wyliesdiesels]

Is this a trick question? Have you checked table 310.15(b)(16) which wouldve answered your question?

 

[Terry D]

#4 copper is good for 85 amps

#6 Aluminum is good for 50 amps

Distance has nothing to do with how many amps can be put through a conductor.

What does determine how many amps can be put through a conductor is:

Size of the conductor

If the conductor is CU or AL

temperature rating of the conductor

Ambient air surrounding the conductor

How many conductors are in the raceway

If the load is a continuous load or not

 

[nadogail]

Thanks for sharing, why is it a concern?

 

[u2slow]

Which has a higher current carrying capacity - a 3’ run of copper 4 gauge or a 6” run of aluminum 6 gauge?

I think I know, just trying to confirm from an expert.

Are we talking about insulation failure? ...or the wire turning to liquid?

Sounds more like a physics/engineering question than a Code question.

 

[DenisG]

Pouillet's Law gives:

1.1823 milli-ohms for 3 ft of 6 AWG copper wire
2.0320 milli-ohms for 0.5 ft of 4 AWG aluminum wire

The copper wire (in this case) has lower resistance (better conductivity).

 

[Terry D]

Pouillet's Law gives:

1.1823 milli-ohms for 3 ft of 6 AWG copper wire
2.0320 milli-ohms for 0.5 ft of 4 AWG aluminum wire

The copper wire (in this case) has lower resistance (better conductivity).

You have the sizes switched.

#4 copper

#6 aluminum

Sent from my SM-G960U using The Garage Journal mobile app

 

[DenisG]

You have the sizes switched.

#4 copper

#6 aluminum

Sent from my SM-G960U using The Garage Journal mobile app

Oops! You're right ... recalculating ...

0.7455 milli-ohms for 3 ft of 4 AWG copper wire

0.3043 milli-ohms for 0.5 ft of 6 AWG aluminum wire

Aluminum wire (in this case) has lower resistance (better conductivity).

 

[mike93lx]

Oops! You're right ... recalculating ...

0.7455 milli-ohms for 3 ft of 4 AWG copper wire

0.3043 milli-ohms for 0.5 ft of 6 AWG aluminum wire

Aluminum wire (in this case) has lower resistance (better conductivity).

That is like the difference between 1000hp and 1010hp

They are effectively the same

 

[kaffine]

Oops! You're right ... recalculating ...

0.7455 milli-ohms for 3 ft of 4 AWG copper wire

0.3043 milli-ohms for 0.5 ft of 6 AWG aluminum wire

Aluminum wire (in this case) has lower resistance (better conductivity).

Ok how does 6 awg aluminum have less resistance than 4 awg aluminum? Looking at the answers in your 2 posts something isn't adding up.

 

[PCustoms]

Ok how does 6 awg aluminum have less resistance than 4 awg aluminum? Looking at the answers in your 2 posts something isn't adding up.

There's a huge difference in length between the 2 samples....

 

[californiaHank]

At 75°C, #6 Cu wire is about 0.491 Ohms per 1000 feet and #4 Al wire is about 0.508 Ohms per 1000 feet. (Source: NEC.)

Since they have about the same resistance per unit length, the NEC gives them the same maximum current ratings.
But, since the two runs are quite different lengths, the power losses are quite different:

3 feet of copper is roughly 3/1000 * 0.491 = approx 0.0015 Ohms
6 inches of aluminum is 0.5/1000 * 0.508 = approx 0.00025 Ohms

The losses in the (longer) copper run are about 6 times greater than in the (shorter) aluminum run.

 

[wyliesdiesels]

this conversation is moot since the allowable ampacity of wire is not dictated by the length of wire...

 

[wyliesdiesels]

#4 copper is good for 85 amps

#6 Aluminum is good for 50 amps

Distance has nothing to do with how many amps can be put through a conductor.

What does determine how many amps can be put through a conductor is:

Size of the conductor

If the conductor is CU or AL

temperature rating of the conductor

Ambient air surrounding the conductor

How many conductors are in the raceway

If the load is a continuous load or not

 

[kaffine]

There's a huge difference in length between the 2 samples....

6 inches in one half a foot in the other

 

[PCustoms]

6 inches in one half a foot in the other

More like 6 inches vs 36 inches...

Oops! You're right ... recalculating ...

0.7455 milli-ohms for 3 ft of 4 AWG copper wire

0.3043 milli-ohms for 0.5 ft of 6 AWG aluminum wire

Aluminum wire (in this case) has lower resistance (better conductivity).

 

[kaffine]

Pouillet's Law gives:

1.1823 milli-ohms for 3 ft of 6 AWG copper wire
2.0320 milli-ohms for 0.5 ft of 4 AWG aluminum wire

The copper wire (in this case) has lower resistance (better conductivity).

Oops! You're right ... recalculating ...

0.7455 milli-ohms for 3 ft of 4 AWG copper wire

0.3043 milli-ohms for 0.5 ft of 6 AWG aluminum wire

Aluminum wire (in this case) has lower resistance (better conductivity).

More like 6 inches vs 36 inches...

Says 0.5ft in each.

 

[PCustoms]

Says 0.5ft in each.

He fixed his math in the 2nd post

 

[themiller]

Thanks all - "current carrying capacity" was a poor choice of words.

I did review 310.15(b)(16), wanted to have my math and head checked was all. Appreciate it. This was more of an academic than a burn the house down type exercise.