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Awg ampicity in short lengths

mikeptag

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Dec 8, 2022
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Im switching out a 45amp battery charger to a 100 amp (12 volt). Between the charger and the battery i have about 2 feet of 6 awg wire to the breaker box where it continues with the main 4/0 awg battery cables another 3-4 feet to the battery. This was fine for the 45 amp charger, but will it still be ok for the 100 amp? I just wanted to confirm the short 6awg run will be ok with the 100 amps. I did find this chart online that tells me it will be (link below), and did a voltage drop calculation that 100 amps in 2 feet of 6awg has just 1-2% voltage drop. However im also reading 6awg wire is rated max is 55 amps. So what does everyone think?

 
Im switching out a 45amp battery charger to a 100 amp (12 volt). Between the charger and the battery i have about 2 feet of 6 awg wire to the breaker box where it continues with the main 4/0 awg battery cables another 3-4 feet to the battery. This was fine for the 45 amp charger, but will it still be ok for the 100 amp? I just wanted to confirm the short 6awg run will be ok with the 100 amps. I did find this chart online that tells me it will be (link below), and did a voltage drop calculation that 100 amps in 2 feet of 6awg has just 1-2% voltage drop. However im also reading 6awg wire is rated max is 55 amps. So what does everyone think?

You need to start with your power demand measured in watts. Then divide by 12V to derive the amps. Then find the right wire size and fuse to protect that wire. In your case you have stated 100A * 12V = 1,200 watt charger. Verify this is correct.

If your highest demand is 100A, then you will need a 4ga pure copper wire. Your distance is close enough so you will not have any appreciable loss at that distance.

So, the answer is no - your 6ga wire will not support 100A continuous. You will need at least 4 ga.

Best,
-Jay
 
You need to start with your power demand measured in watts. Then divide by 12V to derive the amps. Then find the right wire size and fuse to protect that wire. In your case you have stated 100A * 12V = 1,200 watt charger. Verify this is correct.

If your highest demand is 100A, then you will need a 4ga pure copper wire. Your distance is close enough so you will not have any appreciable loss at that distance.

So, the answer is no - your 6ga wire will not support 100A continuous. You will need at least 4 ga.

Best,
-Jay
Double checking I found out in the manufacturer specs (PM3-100-LK)that the 100 amp rating is actually at 15 volts and so 1460 watts after considering efficiency. Would 4awg still work? And how did you arrive at your calculation? Thanks!!
 

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#4 is fine at 100 amps unless the distance is excessive. 2' is not an issue.
#6 is marginal at best and will get warm to hot.
 
Double checking I found out in the manufacturer specs (PM3-100-LK)that the 100 amp rating is actually at 15 volts and so 1460 watts after considering efficiency. Would 4awg still work? And how did you arrive at your calculation? Thanks!!
4 AWG pure copper is found in NEC lookup table, supporting near 100A based on standard temp ranges NTE 90C, properly sized conduit, if used, and proper wire type.

Here is one reference table
www.superb.org/power/nec tables.pdf
 
NEC is great and I prefer 105c marine wire for these connections where unbundled no conduit where #4 is good at 136 to 160 amps depending on ambient heat.
 
NEC is great and I prefer 105c marine wire for these connections where unbundled no conduit where #4 is good at 136 to 160 amps depending on ambient heat.
Good point on considering environmental and jacket for high humidity and vibration. Consider adding car flex liquid tight flexible conduit with proper compression connections for the best installation.
 

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