200A breaker for 175A copper wire?

Is a 200A DC breaker too large for wire that maxes out at 175 AMPS?
I'm assuming the answer is yes.

I'm in Japan and wire sizes are different here, the size of the wire in question is "60 SQ"
Which is between AWG 1/0 & AWG 2/0 in size.

For comparison sake:
AWG 1/0 = 170 Amps = 53.5 SQ
AWG 2/0 = 195 Amps = 67 SQ

Depends on length and whether chassis (free air) or in conduit.

@DIYrich thank you for responding!
Free air, and the length of the wire is 1 meter which is 39 inches, although I could probably reduce the length by half.

According to this, 1/0 wire is good up to 12 feet at 200 amps.

DIYrich said:

According to this, 1/0 wire is good up to 12 feet at 200 amps.

Battery Cable Amperage Capacity Chart - Current and Wire Gauge - ShopSolar.com

Battery cable amperage capacity charts show you how the components in your system relate to the current-carrying wires. Join us as we show you the ins and outs.

shopsolarkits.com

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Ok wow that is a huge relief. Thank you so much @DIYrich

DIYrich said:

According to this, 1/0 wire is good up to 12 feet at 200 amps.

Battery Cable Amperage Capacity Chart - Current and Wire Gauge - ShopSolar.com

Battery cable amperage capacity charts show you how the components in your system relate to the current-carrying wires. Join us as we show you the ins and outs.

shopsolarkits.com

Click to expand...

Do not use those tables for anything!
That website is written by someone who doesn't have clue. Or written by AI-bot.
6 AWG cable for 300A .. for fuck's sake you can as well pour gasoline on your living room as well if you want to burn your house down.

200A breaker for 60mm2 cable is bit too much for every typical installation situation.
200 Cel rated silicone cable buried in wet soil would be ok..

MattiFin said:

Do not use those tables for anything!
That website is written by someone who doesn't have clue. Or written by AI-bot.
6 AWG cable for 300A .. for fuck's sake you can as well pour gasoline on your living room as well if you want to burn your house down.

200A breaker for 60mm2 cable is bit too much for every typical installation situation.
200 Cel rated silicone cable buried in wet soil would be ok..

Click to expand...

@MattiFin so what is the max current carrying capacity of 1 meter of 60mm2?

kolek said:

@MattiFin so what is the max current carrying capacity of 1 meter of 60mm2?

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"it depends"
I have no idea of required code in Japan.
here in Finland 70mm2 cable in free air is rated for 208A in free air installation. Scaled down to 60mm2 it would make 178A
'Murican NEC standard calls for 3/0 cable for 200A fuse if the insulation has the highest 90Cel temperature rating: https://www.usbreaker.com/docs/UL489_US-Breaker_Wire_Size_Chart.pdf

@MattiFin
I'm not saying you're wrong, everything is right there in black and white in your references.
It's interesting though, my inverter is the Deye 8k model, for the battery they recommend 50 SQ wire paired with a 250A fuse. See attached screenprint of the manual.



The 60 SQ cable I have is 17% larger than they recommend, and a 200A breaker is 20% less than the 250A they recommend. Also the 60 SQ KIV cable I have is rated to 217A, so I think I'm probably ok. I also have a 100A T-class fuse on each battery. Would be safer to switch to a 150A breaker though, I agree.

kolek said:

@MattiFin
I'm not saying you're wrong, everything is right there in black and white in your references.
It's interesting though, my inverter is the Deye 8k model, for the battery they recommend 50 SQ wire paired with a 250A fuse. See attached screenprint of the manual.

View attachment 210669

The 60 SQ cable I have is 17% larger than they recommend, and a 200A breaker is 20% less than the 250A they recommend. Also the 60 SQ KIV cable I have is rated to 217A, so I think I'm probably ok. I also have a 100A T-class fuse on each battery. Would be safer to switch to a 150A breaker though, I agree.

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Gazillion standards and countries to cover. NEC for single conductors Table 310.15(B)(17) allows 190A for 2AWG
KIV seem to be 60Cel rated cable so 60mm2 single wire in free air would be abouts 210A with NEC rating. Your 217A sounds suspiciously close to this.

What comes to Deye manual there appears to be error(s) there as 35 and 50mm2 are not same as 2AWG. Fuse sizes also look weird, stepping up from 5kW to 8kW with 1.6x increaase requires 2.5x fuse rating according to that.

@MattiFin Wow that's interesting information on the Sabcable sheet. Appreciate you finding that.
So if the cable supports 210A, do you think I'm safe keeping the 200A breaker, especially given the relatively short length?
I was actually considering giving up on the 200A breaker I already have, and buying a 125A breaker to be extra safe. That might have the added advantage of tripping before and thereby protecting my expensive 100A T-class fuses I have on each of my 2 batteries.

kolek said:

@MattiFin Wow that's interesting information on the Sabcable sheet. Appreciate you finding that.
So if the cable supports 210A, do you think I'm safe keeping the 200A breaker, especially given the relatively short length?
I was actually considering buying a 125A breaker to be extra safe. That might have the added advantage of tripping before and thereby protecting my expensive 100A T-class fuses I have on each of my 2 batteries.

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Should be ok assuming the cables are not buried inside insulation or anything crazy like that. Note that even two cables(minus and plus) bundled together already lower the allowable max current.

@MattiFin Thanks for that clarification. Since you seem so knowledgeable about breakers, I have another related question. My whole house AC breaker at the panel is 3-phase 60A which brings in 100V and 200V. Is it a fire hazard to have a large inverter that can pull more amps / watts than the service panel can provide? I should add that we have never had the 60A house breaker trip, our electrical usage was never that high. And if you prefer I can just put this question up to the forum.

Yo @Hedges has done a good bit of testing with 3 phase and DC breakers. He would be a great person to get in on this.

kolek said:

@MattiFin so what is the max current carrying capacity of 1 meter of 60mm2?

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Length of wire makes no difference for its ampacity, the current it can carry without the I^2R power dissipated causing temperature rise above some level.

What does matter is where the wire goes beyond that length. NEC has a provision that multiple wires in a length of conduit up to 2' long don't require derating. I think that makes sense only if the wire continues on considerably beyond that piece of conduit, so heat is conducted lengthwise and dissipated elsewhere.

If a wire terminates in a breaker, I don't think it can dump energy there, it just raises breaker temperature. If it terminates at a busbar or battery, that may serve as a heatsink.

kolek said:

@MattiFin Thanks for that clarification. Since you seem so knowledgeable about breakers, I have another related question. My whole house AC breaker at the panel is 3-phase 60A which brings in 100V and 200V. Is it a fire hazard to have a large inverter that can pull more amps / watts than the service panel can provide? I should add that we have never had the 60A house breaker trip, our electrical usage was never that high. And if you prefer I can just put this question up to the forum.

Click to expand...

Obviously if you draw or backfeed more than 60A (or more than 48A, since we like 25% margin), it may trip. That breaker and the utility feed will be protected.

Your inverter may be able to supply additional loads for the house from battery, using CT to measure current at grid connection and stay under 48A. "Additional Local Consumption."

The problem would be if grid 60A plus inverter 40A puts 100A into your wires or breaker panel and that exceeds what those parts can handle.
That could be downstream, or could be in another branch your inverter backfeeds to.

Our "120% Rule" and other versions are designed to protect against that.
I've determined that neutral wire can end up carrying the sum of available grid current and available inverter current. 120% rule puts a limit on how much it would overheat the wires (about 30C beyond the intended 75C or 90C).


It would help if you sketched out your topology, gave values of relevant breakers, wire gauge and breaker panel specs, link to inverter.

@Hedges Thank you for your detailed response, I haven't had time today but I will respond with my topology info asap. Thanks again!