I got this bolt on terminal fuse block that has a 5/16 fuse holder bolt where the cable attaches. My cable has 3/8 lugs. Is is okay to use the 3/8 lug (it is snug when bolted down) or should I redo the cable with 5/16 lug?
3/8 Lug on 5/16 Bolt
- Thread starter dmholmes
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Ampster
Renewable Energy Hobbyist
To me it is all about surface area contact for the Amps traveling through the connection. I don't have a picture of your particular connection so I can't say for sure. If it is like my Bussman fuses there is not inside contact surface between the 3/8" diameter of the fuse surface and the 5/16 bolt so in that case I would just make sure the lug contacts all of the fuse contact area.
Ampster
Renewable Energy Hobbyist
I had forgotton how small that ring was on the fuse and how narrow some ring terminals are. I would change out to a 5/16 ring terminal or a bigger lug if you are carrying more than 100 Amps continuously.
12 AWG, for my Renogy Wanderer 10A SCC to battery. The fuse is for my 2 AWG inverter to battery cable, too lazy to grab it from the garage for the photo.
The SCC also needs a 10A fuse to the battery according to Renogy. Is that correct?
John Frum
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Use a 15 amp fuse and don't worry about the size mismatch because the ampacity is small.
Ampster
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That could carry 100 Amps so it depends on the fuse or what you expect the circuit needs to carry.
Thanks, will do. That’ll have to be ANL/inline?
That’s a 125A fuse for a 1200W inverter. 2 AWG cable.
John Frum
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Atc
Ampster
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As long as that is the correct fuse for that wire size you should be okay if you make sure the fuse surface contacts the lug all the way around.
For the benefit of future readers #2 wire is better protected by a 100 Amp fuse but a short length in the air may not be an issue.
For the benefit of future readers #2 wire is better protected by a 100 Amp fuse but a short length in the air may not be an issue.
I’m not entirely certain as I’ve seen fuse sizing based on load and also wire size. The 1200W inverter came with 5 AWG wire. I’m using a 2 AWG wire I had made just in case.
Will’s book mentions a case of using a smaller fuse than otherwise indicated with a larger cable. But then gives recommendations for inverter fuses based on wattage.
Should the fuse be based on my 1200W inverter or my 2 AWG cable?
Ampster
Renewable Energy Hobbyist
The fuse is to protect the wire. The fuse and wire should be sized to handle the Inverter load, which in your case the wire will easily handle the load. On a short circuit the fuse will blow quickly. If the inverter surges above 100 Amps the wire can handle it for a while before getting too hot and your fuse won't blow. I am more specific and conservative with wires in my home inside conduit but wire in the open air can tolerate more heat and Amperage. You will probably get several opinions.
You are asking all the right questions.
chrisski
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I am installing my inverter now on my system, and wattage is a small part of it. I am doing a 2000 watt inverter on a 12 volt system, which I am putting 2/0 cable on, which will be good provided I don't make the cable too long.
To figure out the max cable length for any gauge of wire, I am going to any number of online calculators, and most require out and back, so a 5' run of wire gets calculated at 10'
When charging my batteries at my house, I have 5/16 on my batteries that I have 3/8 eyelets for, but that is 26 amps. I only do this because the batteries will not see a lot of amps.
For the electric board I'm putting together, I make sure that the eyelet matches the stud size, and both are rated for voltage and amps I plan to use. I have a mixture of stud sizes of 3/8 and 5/16. So I will have both those sizes.
The battery bank for the inverter is fused at 350 amps, so all the other components are greater than that.
Those bigger eyelets and wires are becoming challenging to route. I have found that in addition to normal eyelets, 90° eyelets is making cable production easier and shorter, but wish they made 60° 30° and 45° eyelets also.
To figure out the max cable length for any gauge of wire, I am going to any number of online calculators, and most require out and back, so a 5' run of wire gets calculated at 10'
When charging my batteries at my house, I have 5/16 on my batteries that I have 3/8 eyelets for, but that is 26 amps. I only do this because the batteries will not see a lot of amps.
For the electric board I'm putting together, I make sure that the eyelet matches the stud size, and both are rated for voltage and amps I plan to use. I have a mixture of stud sizes of 3/8 and 5/16. So I will have both those sizes.
The battery bank for the inverter is fused at 350 amps, so all the other components are greater than that.
Those bigger eyelets and wires are becoming challenging to route. I have found that in addition to normal eyelets, 90° eyelets is making cable production easier and shorter, but wish they made 60° 30° and 45° eyelets also.
So the 2 AWG wire can handle 175A. The 1200W inverter’s max surge is 2400W, or 200A on the battery side. It sounds like a 125A fuse is useless in this context?
Does that indicate a 250A fuse based on the inverter’s max surge? Or better to stick with 5 AWG cable and fuse that with 125A fuse?
Does that indicate a 250A fuse based on the inverter’s max surge? Or better to stick with 5 AWG cable and fuse that with 125A fuse?
chrisski
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IMO, it's real important to run the DC calculator, or do the formula. I may be misreading your link, but that doesn't seem to take into account if for some reason, someone wanted to install the inverter 25 feet away from the batteries, although it does give you ohms for the wire, so you could use the formula. Using too long of a 2 AWG run will have a significant voltage loss at higher loads. I have a larger inverter, and you have a decent sized inverter for a 12 volt system, that I can't off the top of my head say is OK, but I can say normal runs in a good RV setup won't require large 2/0 wire like an inverter twice your size will.
When I used the voltage calculator for my panel setup, I had wanted to run all six of my 100 watt panels in parallel with a six string combiner, but then the wires became thicker than 10 gauge, so what I did was run three in parallel and three in series and met the 10 gauge criteria. Going up in amps or down in volts in the same sized wire got me too much voltage loss, although my wires were rated for amps.
For fuse, NEC code would be the best. I don't know NEC code, so I was told on this board a formula, and I've seen it put out a couple of times: divide the wattage of the inverter by the low voltage cutoff of the inverter, and multiply this by 1.5 and that can be the amount of amps to draw, and multiply that by 1.2. This got me a 342 amp fuse, which the next up is 350 amps.
Amps change considerably based off of voltage. Its a 12 volt inverter so this shows you the difference in amperage at 12 volts:
And then since it rarely will be down to 12, and maybe charging at 13.8 this is the difference in amperage.
All those examples are 2000 watts, it's just the voltage / amperage that makes the fuse different. In a way it shows why sizing wires is important. They get a lot less amps to make 2000 watts or whatever watts you're using with less voltage lose.
When I used the voltage calculator for my panel setup, I had wanted to run all six of my 100 watt panels in parallel with a six string combiner, but then the wires became thicker than 10 gauge, so what I did was run three in parallel and three in series and met the 10 gauge criteria. Going up in amps or down in volts in the same sized wire got me too much voltage loss, although my wires were rated for amps.
For fuse, NEC code would be the best. I don't know NEC code, so I was told on this board a formula, and I've seen it put out a couple of times: divide the wattage of the inverter by the low voltage cutoff of the inverter, and multiply this by 1.5 and that can be the amount of amps to draw, and multiply that by 1.2. This got me a 342 amp fuse, which the next up is 350 amps.
10.5 | Low voltage cutoff |
2000 | Inverter rating |
190.4762 | Expected Amps |
285.7143 | Expected Amps * 1.5 |
342.8571 | Fuse rating |
Amps change considerably based off of voltage. Its a 12 volt inverter so this shows you the difference in amperage at 12 volts:
12 | Battery rated voltage | |
2000 | Inverter rating | |
166.6667 | Expected Amps | |
250 | Expected Amps * 1.5 | |
300 | Fuse ratin is Expected safety margin in amps *1.2 |
And then since it rarely will be down to 12, and maybe charging at 13.8 this is the difference in amperage.
14.8 | Battery charging voltage |
2000 | Inverter rating |
135.1351 | Expected Amps |
202.7027 | Expected Amps * 1.5 |
243.2432 | Fuse ratin is Expected safety margin in amps *1.2 |
All those examples are 2000 watts, it's just the voltage / amperage that makes the fuse different. In a way it shows why sizing wires is important. They get a lot less amps to make 2000 watts or whatever watts you're using with less voltage lose.
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