Safe to mix 4/0 and 1/0?

solarstuff · Sep 17, 2020

Rookie mistake, please help?

I have a 2200w inverter so have bought 4/0 + and - cables to move from inverter to batteries.
The 1 awg that was there heated up under 1000w loads or higher.

But I forgot about the fuse/circuit breaker.
(fuse now, breaker screwed on panel but won't use til ironing this out).

Can I mix 4/0 awg from inverter down to breaker with 1/0 from breaker down to batteries?
Or do I need 4/0 all the way to avoid overheating?

snoobler · Sep 17, 2020

Do you have 1awg or 1/0awg? They are different.

Wires are supposed to heat up when used anywhere near their current rating, and current ratings for various wires are based on temperature.

Using larger wires is fine, but you should fuse/breaker for the thinnest wire in the circuit. The shorter wire will have less total resistance, but it may still get warm. Please see the chart in link #2 in my signature. It is the AWG chart, and it shows wire ratings for different temperatures. Note that the lowest listed is 125A @ 60°C. 60°C is effing HOT to the touch. 175A @ 90°C will almost boil water. Marine ratings go to 105°C, which can boil water.

FWIW, 2X 1/0 wires are almost identical to a single 4/0 wire. If you double up the 1/0, you have 4/0 the whole way.

solarstuff · Sep 17, 2020

I'm installing 4/0 from inverter to fuse/breaker on positive (and negative to battery) and HOPE I can install 1/0 (or 2 lenghts of 1/0 to share load, if I understand you correctly) from fuse/breaker to battery bank.

The battery bank is connected like this:

4/0 positive + in from inverter to fuse
1/0 (or 2 strands of 1/0) from circuit breaker to battery 1

battery 1 has 1awg to battery 2 (on both + & -)
battery 2 has 2awg to battery 3 (on both + & -)
battery 3 has 1awg to battery 4 (on both + & -)

then 4/0 out of bank to inverter negative.

So far so good

solarstuff · Sep 17, 2020

I have a 250a inline fuse right now, and a 250a tocas breaker screwed in right next to in on the board
(I didn't want to switch over until I sorted out my wiring).
PS: Thanks for the links/wisdom.

snoobler said:
Do you have 1awg or 1/0awg? They are different.

Wires are supposed to heat up when used anywhere near their current rating, and current ratings for various wires are based on temperature.

Using larger wires is fine, but you should fuse/breaker for the thinnest wire in the circuit. The shorter wire will have less total resistance, but it may still get warm. Please see the chart in link #2 in my signature. It is the AWG chart, and it shows wire ratings for different temperatures. Note that the lowest listed is 125A @ 60°C. 60°C is effing HOT to the touch. 175A @ 90°C will almost boil water. Marine ratings go to 105°C, which can boil water.

FWIW, 2X 1/0 wires are almost identical to a single 4/0 wire. If you double up the 1/0, you have 4/0 the whole way.

Ampster · Sep 17, 2020

As @snoobler said, you can use any wire you want as long as the fuse protects the smallest wire. In your case the smallest wire is 2 AWG. You could put a smaller fuse on that wire but a 250 Amp fuse will not protect 2 AWG wire.

solarstuff · Sep 17, 2020

The fuse bnetween battery and inverter is where the whires heat up.
What size fuse should I be using bewtween them? Or should I replace the 2 wire with 1?

Ampster said:
As @snoobler said, you can use any wire you want as long as the fuse protects the smallest wire. In your case the smallest wire is 2 AWG. You could put a smaller fuse on that wire but a 250 Amp fuse will not protect 2 AWG wire.

Ampster · Sep 17, 2020

solarstuff said:
What size fuse should I be using bewtween them? Or should I replace the 2 wire with 1?

You can replace the wire or you can go to the table mentioned above and use the correct fuse for the existing wire. The choice is yours. If it were me, I would base it on what I had in my spare parts bin and how much load I expected that connection to have.

solarstuff · Sep 17, 2020

Is moving up to 1 awg on the battery enough for the fuse?
The Max load I will draw is 1500w at any one time.

Thx in advance!

Ampster · Sep 17, 2020

What does the chart say? I would have to look that up to answer your question.
1500 Watts is how many Amps at 12 volts?

John Frum · Sep 17, 2020

solarstuff said:
Is moving up to 1 awg on the battery enough for the fuse?
The Max load I will draw is 1500w at any one time.

Thx in advance!

Depends on your system voltage and the round trip circuit length.
If you have a 1500 watt inverter at 12 volts....
1500 ac watts * 1.15 inverter efficiency / 12 volts = 143.75 dc amps
143.75 dc amps * 1.25 fuse headroom = 179.6875 fuse amps

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

John Frum · Sep 17, 2020

Somebody should whip up a web page that does this.

John Frum · Sep 17, 2020

I feel my joie de vivre waning.

GLC · Sep 17, 2020

smoothJoey said:
Depends on your system voltage and the round trip circuit length.
If you have a 1500 watt inverter at 12 volts....
1500 ac watts * 1.15 inverter efficiency / 12 volts = 143.75 dc amps
143.75 dc amps * 1.25 fuse headroom = 179.6875 fuse amps

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

Just a question, if he has 144 amps to account for, why are the wires heating up with using 1/0 wire when the calculator shows wire as small as #4 ? I understand that there is energy loss but I have #2 wires that regularly pull 1000 to 1500 watts from my inverter and they stay pretty cool. Now if they start pulling 2500 watts they do start heating up. Of course my wires are only 2 foot long.

GLC · Sep 17, 2020

GLC said:
Just a question, if he has 144 amps to account for, why are the wires heating up with using 1/0 wire when the calculator shows wire as small as #4 ? I understand that there is energy loss but I have #2 wires that regularly pull 1000 to 1500 watts from my inverter and they stay pretty cool. Now if they start pulling 2500 watts they do start heating up. Of course my wires are only 2 foot long.

Ok, I may have figured it out, I am running 24 volts not 12. DUH

John Frum · Sep 17, 2020

GLC said:
Just a question, if he has 144 amps to account for, why are the wires heating up with using 1/0 wire when the calculator shows wire as small as #4 ? I understand that there is energy loss but I have #2 wires that regularly pull 1000 to 1500 watts from my inverter and they stay pretty cool. Now if they start pulling 2500 watts they do start heating up. Of course my wires are only 2 foot long.

how hot are the wires actually getting?

GLC · Sep 17, 2020

smoothJoey said:
how hot are the wires actually getting?

Warm to touch but can still hold them. It would have to be sustained over 2500 watts though to get that warm.

John Frum · Sep 17, 2020

GLC said:
Warm to touch but can still hold them. It would have to be sustained over 2500 watts though to get that warm.

Its not the watts its the amps.

GLC · Sep 17, 2020

smoothJoey said:
Its not the watts its the amps.

Ok I get it, since mine is 24 volt at 1500 watts that would be a little over 63 amps for me.

John Frum · Sep 17, 2020

GLC said:
Ok I get it, since mine is 24 volt at 1500 watts that would be a little over 63 amps for me.

1500 watts @ 24 volts ...
1500 * 1.15 / 24 = 71.875 dc amps
71.875 * 1.25 = 89.834375 fuse amps
Ohhhh the lights are getting dim. ?

GLC · Sep 17, 2020

smoothJoey said:
1500 watts @ 24 volts ...
1500 * 1.15 / 24 = 71.875 dc amps
71.875 * 1.25 = 89.834375 fuse amps
Ohhhh the lights are getting dim. ?

I am just learning and asking questions. That is why I do not understand the Bos'ns calculator. Even at 89 amps it still shows wire at #6 is ok?

Safe to mix 4/0 and 1/0?

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