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Old 04-22-2013, 03:38 PM   #15
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Thanks Mike, good info. 3/0 batt home run sounds like the least to go with. Not to get to personal but dose your DW consider you a know it all or is she an engineer also?
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Old 04-22-2013, 04:52 PM   #16
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If you really want to know it all, ask my wife. I call her EngineerAnnie.
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Old 04-22-2013, 05:24 PM   #17
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I knew it! Behind every good man stands a great women.In your case its' Engineer Annie.
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Old 04-22-2013, 09:41 PM   #18
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EM - I wonder why larger wire (2 AWG) carries less current than smaller wire (3 AWG, 4 AWG). Are they all copper?
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Old 04-23-2013, 12:38 AM   #19
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Steve- AWG is backward, #30 is hair thin, #1 is fat. It was explained to me this way- "gauge" is the number of strands of the diameter in question that fit within a prescribed size circle. So 30 of the #30 wire fit in the diameter of a #1 wire. Above #1 you go to "ought" gages w/more oughts = fatter wire, 1-ought or 1/0, then 2/0, 3/0, 4/0. Then for big work comes MCM or thousand circular mils- 250mcm, 300, 350, 400, 500, 600, 750, 1000mcm. Tables go higher but nobody in the real world uses bigger stuff, you start running parallel "strands."

But, to your question, standard ampacity tables always show higher values for fatter wire of the same construction type. Wire type varies by method of stranding (solid, fat strands, skinny strands, hair-like strands, w/more strands per given gauge diameter = more ampacity), but also by insulation type. Some insulations qualify for higher heat tolerance therefore can pass more amperes per gauge thickness.
In the chart linked above, #3 XHHW-2 Cu wire has insulation rated for 90*C & 110A, whereas #2 Cu wire w/UF-B insulation only qualifies for 60*C temp usage and therefore maxes out at 95A. The Cu is the same in each but the insulation differs. #2 Flexoprene (welding cable) is rated at 200A, quite a difference, but that's more because of the stranding than the insulation.

I once did a job in Oakland CA connecting a couple of pallets of batteries in the 2nd basement to radio equipment on the 4th floor; because of the length of the run, to control volt drop it took 128 strands of 750mcm wire that was built like welding lead (even so, to bend each strand into place they hammered it using a mallet). The column of wire weighed something like 16,000lbs for the 6 floor vertical run, and was a serious structural project in addition to an electrical one.
Good times. That was some dreamy wire. Sigh....
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Old 04-23-2013, 05:53 AM   #20
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I have a head ache!
I think he said nothing is bigger than something and more nothings is bigger than less nothings.
I guess you just have to remember if you are talking about something or nothing to know if more is smaller or bigger.
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Old 04-23-2013, 08:19 AM   #21
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2 tylenol mo betah than 1 tylenol.
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Old 04-23-2013, 08:21 AM   #22
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Its difficult to comment on this thread--I feel so unqualified. Anyway, I agree that at continuous max draw [inverting], a 3000 watt inverter with 8-10 feet of run [eg you decide to put the inverter in a forward basement compartment] would need 3/0 or better yet, 4/0 cable. My simple thinking is that with a 2000watt inverter, 2/0 will handle continuous charging at 100-120 DC amps [which by the way drops off prettty quickly once you get to absorb stage] and will probably handle short bursts of 2000 watts of max inverting while both the microwave and the hair dryer are running. Not very scientific but I have never "measured" temps on 2/0 cables using my highly developed "hand" sensors and felt excessive heat. Not sure I would "spring" for 3-4 ought cable with a 2000watt inverter, that is, unless someone else was paying for it--like insurance.
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Old 04-23-2013, 10:46 AM   #23
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EM - After studying your reply and receiving my PHd in wireology my question still remains. The wire gauge indicated from the tables in your post indicate less current for larger wire...I think. That was my question...why? I assume "ampacity" is the amount of current they carry. Were the wires of different metals or construction? See your table below.

Standard Wire & Cable Co. makes Flexoprene brand welding lead used in my rig, ampacities:
2/0- 375A
3/0- 450A
4/0- 550A per their tables
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Old 04-23-2013, 11:10 AM   #24
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I think in his lecture EngineerMike said that once you get to the large "ought" size wire (larger than #1 wire size), the larger number, the larger the wire. So 4/0 is bigger than 3/0, and 3/0 is bigger than 2/0. So yes, larger wire carries more current as the Standard Wire & Cable chart shows. (Assuming construction is the same. I read that somewhere recently.)

Most of us aren't used to the ought sized wire. We are used to the larger gauge size, the smaller the wire.

He also said #2 wire is bigger than #3 wire, and #3 wire is bigger than #4 wire. So you will find that #2 carries more current than #3. Just the opposite with the smaller wire, and what we small minded people are used to. (Wait, that didn't come out right.)
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Old 04-23-2013, 08:18 PM   #25
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^ Yep 4/0 is just shorthand for 0000 which is bigger than 000 and so on.

sizes go 4, 3, 2, 1, 0, 00, 000, 0000 and up
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Old 04-23-2013, 08:21 PM   #26
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What Jim & Dave said.
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Old 04-23-2013, 10:23 PM   #27
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Let's ask Engineer Annie and put this baby to bed.
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Old 04-23-2013, 10:32 PM   #28
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Quote:
Originally Posted by JLMunsil View Post
I have a head ache!
I think he said nothing is bigger than something and more nothings is bigger than less nothings.
I guess you just have to remember if you are talking about something or nothing to know if more is smaller or bigger.
ROTFLMBO!!!! Truly your intellect is dizzying.
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