Appropriate wire gauge question

[zanydroid]

The 80% rule is only for continuous loads (>3 hours). There is also an 80% rule for the largest single appliance you can plug into a circuit, does not apply for hardwire. The combination of these leads a lot of people to assume there is a flat 80% rule all the time. (Good thing they don’t get confused about the 50% rule that applies in some other situations)

 

[chrisski]

are you recommending 300A class T fuse and 250mcm wire rated 90C ?

I recommend wire that is rated for 300 amps and a 225 amp class T fuse. My 4/0 welding wire is rated for 300 amps. The 300 Amp OCPD and 250 MCM wire is what we recommended to me.

A manufacturer’s spec sheet on a wire will show what the rating is. Those are not easy to find and most ads I see do not contain a link or the manufacture’s website does not have this data.

For the 225 amp class T fuse, I do not reccomend using a 2000 watt inverter for 2000 watts very long. I recommend using it for 1000 watts hours on end briefly going to 2000 watts a couple of minutes at a time for 5 or 6 times a day.

My recommendations are extremely conservative. I am not the NEC. I build for my needs.

These are some of the posts I used to set my limits.

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I believe in the following limits:

1000 watts 12 vols
2000 watts 24 volts
4000 watts and above, 48 volts

IMO, It’s also OK to get an inverter greater than that to cover surge ratings for inductive motor start up and to briefly go above those limits, provided the inverter is wired to run it.

 

[chrisski]

The 80% rule is only for continuous loads (>3 hours). There is also an 80% rule for the largest single appliance you can plug into a circuit, does not apply for hardwire. The combination of these leads a lot of people to assume there is a flat 80% rule all the time. (Good thing they don’t get confused about the 50% rule that applies in some other situations)

Thanks. That is what I’m trying to say With multiplying the 1.25 at the end of the formula.

I truly do not like what “guests” have done to my system to unknowingly stress it out. THat’s another reason I will continue to use this 1.25 / 80% rule.

I also argued with the electrician that was installing my 48 amp Tesla charger that the circuit breaker needed to be 60 amps like the manual says and the 1.25 rule says and not 50 amps like he wanted to install. He said the 80% rule did not apply. I tried looking the 80% / 1.25 rule up in the 2023 NEC code, but did not find it.

 

[Ton618]

A manufacturer’s spec sheet on a wire will show what the rating is. Those are not easy to find and most ads I see do not contain a link or the manufacture’s website does not have this data.

For TEMCo welding cable:

TEMCo WC0001 Welding Cable - 2/0 AWG 5 ft - Black

temcoindustrial.com

 

[OffGridForGood]

I recommend wire that is rated for 300 amps and a 225 amp class T fuse.

If the fuse is 225A, do we need more than 250A wire?

 

[zanydroid]

I also argued with the electrician that was installing my 48 amp Tesla charger that the circuit breaker needed to be 60 amps like the manual says and the 1.25 rule says and not 50 amps like he wanted to install. He said the 80% rule did not apply. I tried looking the 80% / 1.25 rule up in the 2023 NEC code, but did not find it.

There's an explicit section in article 625 about this. It has been there probably since 2011 or 2014, if not 2008. Electrician is really bad.

(also if the manual says to do it, you have to do it. there's another section in NEC for this)

Towns with a lot of EVSE installation call this out explicitly too.

 

[Reed Cole]

For my inverter, I use welding wire which has an ampacity in excess of the NEC chart.

Do you know why welding wire has higher ampacity?

 

[Hedges]

I usually can't hold a continuous arc for 3 hours.

 

[Reed Cole]

I usually can't hold a continuous arc for 3 hours.

View attachment 188065

Maybe you need a longer rod?

 

[glandpuck]

I'm a little confused over using welding cable. My understanding is that welding cable with an EPDM rubber jacket is really meant to be used in settings where is welder may have the cables on the floor of the workplace settings and moving around the floor to different positions on a project or out at a jobsite. Sort of where the rubber meets the road and there could be a risk of exposure to hazardous materials and liquids.

On the other hand, my understanding of using a 1/0, 2/0, 3/0, 4/0 Type MTW/UL1284 Wire, 1672 Strand is more appropriate for installations where the wires may be in conduits and for electrical hookups rather than welding machines. This is PVC coated.

What does the NEC say on these differences and applications?

 

[zanydroid]

Do you know why welding wire has higher ampacity?

Some combination of higher temp insulation or more relaxed requirements than NEC.

Higher temp insulation only helps you if the things you connect to can handle it

 

[robbob2112]

I have the LiTime brand 200ah Plus battery. It has a 200amp BMS in it but I haven't got any plans to push it.

I also have a 2000w Expertpower inverter/charger with auto transfer switch. Originally I ordered a 3000w version but cancelled and reordered the 2000w. Smallest unit I could find that ran on 12 volts and had a UPS like function. Turned out the fans in it were way to loud for my purposes and I ordered a victron phoenix 1000w inverter (1200VA).

The 2/0 I originally ordered had already shipped along with lugs so I kept it and used it. It was for the 3000w unit originally and is rated for 450 amps at my short run of 2ft. Probably more, but the chart I used only went down to 50ft.

The 2000w version came with 2 awg battery wire and when I was testing with a resistive load (space heater) I pulled a bit over 190 amps according to the smartshunt and the wires didn't even get warm after an hour.

The difference between regular wire, battery wire, and welding wire is all about conductor count and insulation type.

Regular 2 awg THHN is stiff and has what looks like a PVC sheath. Conductor count is 19. Temp rating generally 90c.
Battery wire 2 awg has 133 conductors in it with either PVC (automotive 90c) or rubber sheath (other 105c) depending on use.
Welding wire 2 awg has 625 conductors in it with a rubber sheath and is rated 105c or better.

Welding wire is also far easier to bend than the other two and has a thicker rubber sheath. You can get regular 2 awg in 105c as well. You can get any of the wires in a chemical resistant sheath as well.

More conductors equals less resistance per foot and better heat dissipation.

My final configuration is with the 2 awg welding wire with a 125amp MRBF fuse at the battery terminal which is rated for 10,000 AIC. I could downsize to 100amps I think but if there is a short it will pull way way more than that 125a.

 

[zanydroid]

More conductors equals less resistance per foot and better heat dissipation.

AWG is corrected for cross section area and there is no such thing as a difference in skin effect for stranded either unless the strands are individually insulated.

Strands have mechanical advantages like flexibility. I can’t remember which one handles vibration better (stranded or solid).

How do you know your terminations can handle 105C?

 

[robbob2112]

AWG is corrected for cross section area and there is no such thing as a difference in skin effect for stranded either unless the strands are individually insulated.

Strands have mechanical advantages like flexibility. I can’t remember which one handles vibration better (stranded or solid).

How do you know your terminations can handle 105C?

Honestly I hadn't thought about it. They are marine grade heavy duty tinned copper lugs from Ancor.

Like this but with a #10 hole.. https://nvnmarine.com/products/59524-ancor-heavy-duty-lugs-2-gauge

Sorry, forgot which ones I bought where... here is the link - selterm lugs -

Amazon.com

 

[zanydroid]

Honestly I hadn't thought about it. They are marine grade heavy duty tinned copper lugs from Ancor.

Ancor Heavy Duty 6 AWG #10 Tinned Lug - 25-Pack

Buy with the best price Ancor Heavy Duty 6 AWG #10 Tinned Lug - 25-Pack MPN: 242243 UPC: 091887242027 from NVN Marine! Same day shipping before 3pm.

nvnmarine.com

Got it. Terminations also include whether the things on the other end that you connect to (battery and inverter) can handle that temp. In the absence of info 75C or 60C is what I use. (60C if it’s not labeled)

I quickly googled a shunt and it says 50C ambient limit (Victron). What are people using as the temp rating of a bus bar with a 50C max device on it? The bus bar will dissipate some heat, sure

 

[robbob2112]

Got it. Terminations also include whether the things on the other end that you connect to (battery and inverter) can handle that temp. In the absence of info 75C or 60C is what I use. (60C if it’s not labeled)

I quickly googled a shunt and it says 50C ambient limit (Victron). What are people using as the temp rating of a bus bar with a 50C max device on it? The bus bar will dissipate some heat, sure

On the victron smartshunt I got the temp sensing wire to use with it and the post temperature and it never leaves 27c, basically a bit above room temperature. Good crimp, good contact, I wouldn't expect much of a temp increase. At least not at the minimal load I am putting on it.

I still have a lot to learn before I am ready to do a my solar install with battery bank. But I have a year or more and the Mike Holt book for reference.

 

[glandpuck]

I have the LiTime brand 200ah Plus battery. It has a 200amp BMS in it but I haven't got any plans to push it.

I also have a 2000w Expertpower inverter/charger with auto transfer switch. Originally I ordered a 3000w version but cancelled and reordered the 2000w. Smallest unit I could find that ran on 12 volts and had a UPS like function. Turned out the fans in it were way to loud for my purposes and I ordered a victron phoenix 1000w inverter (1200VA).

The 2/0 I originally ordered had already shipped along with lugs so I kept it and used it. It was for the 3000w unit originally and is rated for 450 amps at my short run of 2ft. Probably more, but the chart I used only went down to 50ft.

The 2000w version came with 2 awg battery wire and when I was testing with a resistive load (space heater) I pulled a bit over 190 amps according to the smartshunt and the wires didn't even get warm after an hour.

The difference between regular wire, battery wire, and welding wire is all about conductor count and insulation type.

Regular 2 awg THHN is stiff and has what looks like a PVC sheath. Conductor count is 19. Temp rating generally 90c.
Battery wire 2 awg has 133 conductors in it with either PVC (automotive 90c) or rubber sheath (other 105c) depending on use.
Welding wire 2 awg has 625 conductors in it with a rubber sheath and is rated 105c or better.

Welding wire is also far easier to bend than the other two and has a thicker rubber sheath. You can get regular 2 awg in 105c as well. You can get any of the wires in a chemical resistant sheath as well.

More conductors equals less resistance per foot and better heat dissipation.

My final configuration is with the 2 awg welding wire with a 125amp MRBF fuse at the battery terminal which is rated for 10,000 AIC. I could downsize to 100amps I think but if there is a short it will pull way way more than that 125a.

My 3/0 MTW wire is 1672 fine stranded, bends real easy like welding wire.

I think EPDM should be used if in the open, MTW if going into conduits. I think the price is about the same per foot.