100A Sub Panel

[j2ritt]

Hi,

I'm running electric to my shop. The building is around 300' from my house, maybe a little more from panel to panel.

I am in the process of having a new septic system installed which basically requires us to dig a trench from the house to within 20' of the shop. So, the plan is to bury conduit in the trench for the septic system at the same time.

I'd like to run 100A service. I haven't done load calculations, but my thought is I'd rather spend a little extra now than potentially have too much draw in the future. Future plans involve a heatpump split unit, welder, etc. so I just don't want to run into too much draw down the road if I can avoid it.

Since I need to run conduit anyways - I was considering using XHHW-2 AL 2/0 runs, instead of MHF since it's a little cheaper and more pliable and will be enclosed in conduit either way. Thinking I need (3) runs of XHHW-2 AL 2/0 for 2 hots and a neutral + (1) run of #1 AL for ground. Does that sound right?

thanks in advance
Josh

 

[pattenp]

It's best to calculate full anticipated loads. At 300ft a total load of 80A will be a little over the recommended 3% voltage drop using 2/0 Al.

 

[larry4406]

I used 2" conduit to my barn and the pull was easy. I also put in a 1" conduit for future communications.

 

[j2ritt]

It's best to calculate full anticipated loads. At 300ft a total load of 80A will be a little over the recommended 3% voltage drop using 2/0 Al.

ok, after some rough calculations I wouldn't expect load to be more than 50amps at any given time. Even that may be high, I was imagining peak load time would likely be if an AC is running while I'm using a welder. Other than that it would be 1 or 2 woodworking tools being us at the same time and maybe a split AC unit if I put one in eventually.

Also - I remeasured the distance and the run will actually be 250'

Looking at Southwire's Voltage Drop Calc it looks like 80amps is within the limits of 2/0 AL for that run.

So - I think what I need is:
2/0, 2/0, 2/0, #6 wires with an 80 Amp (2-Pole) Breaker

Sound reasonable/logical?

appreciate the help

 

[mike93lx]

I'd downsize the neutral. 2/0 is necessarily large.

I don't know if you will be able to land a 2/0 on an 80a breaker. Either way, I'd probably just do a 100a.

 

[theoldwizard1]

Classic GJ OVERKILL !!!

The MOST COOMON feed to a "one man" shop is 60A. You can easily run A/C-heat pump and a welder. Worst case maybe a plasma cutter because you need to have the compressor on at the same time. Turn off the A/C.

With a 60A feed, you can probably get away with 1/0 or maybe even 2.

IT'S YOUR $$$$ !

 

[dave*99]

Sometimes folks anticipate an EV charger in the future so larger services are considered. I don't expect to have an EV but I suppose the next owner of my place might/will. Not looking to start an EV debate. And yes I know you can charge at lower rates than 48A. Given the push for electrification of everything, a "one man shop" is still a building that may in the future have greater load.

I ran into the POCO man changing out the meter on the 3200 sf house next door. It has 320/400A service. He commented that most of the new houses in the area have that size service. And that same house has natural gas heat, water heaters and cooking. The largest load in that place are the (2) three ton AC units and the hot tub.

 

[mike93lx]

Sometimes folks anticipate an EV charger in the future so larger services are considered. I don't expect to have an EV but I suppose the next owner of my place might/will. Not looking to start an EV debate. And yes I know you can charge at lower rates than 48A. Given the push for electrification of everything, a "one man shop" is still a building that may in the future have greater load.

I ran into the POCO man changing out the meter on the 3200 sf house next door. It has 320/400A service. He commented that most of the new houses in the area have that size service. And that same house has natural gas heat, water heaters and cooking. The largest load in that place are the (2) three ton AC units and the hot tub.

320a is standard in my neighborhood, and we have gas.

While people might want an EVSE in the future, charging is ge really done overnight when not many high draw tools are in use. I really don't think it changes the math in 98%+ of cases

 

[dave*99]

320a is standard in my neighborhood, and we have gas.

While people might want an EVSE in the future, charging is ge really done overnight when not many high draw tools are in use. I really don't think it changes the math in 98%+ of cases

What drives the move to 320A with gas service in place?

 

[mike93lx]

What drives the move to 320A with gas service in place?

My guess it's a mix of "just because" and it's a highlight on the listing. Larger houses need lots of circuits, so it either needs a massive 200a panel or two 200's. If you're putting in two 200's, might as well go 320a.

My panels are mostly full but even with all three ac's and the pool heater running, I wouldn't hit 200a of draw

 

[mm08822]

My guess it's a mix of "just because" and it's a highlight on the listing. Larger houses need lots of circuits, so it either needs a massive 200a panel or two 200's. If you're putting in two 200's, might as well go 320a.

My panels are mostly full but even with all three ac's and the pool heater running, I wouldn't hit 200a of draw

It becomes a notable selling point vs. just having to spend a lot of $$ to properly protect the 200A SE cable and meter that gets no mention. Two panels fed off of a 320A meter pan with dual lugs is easier to install.

 

[wyliesdiesels]

ok, after some rough calculations I wouldn't expect load to be more than 50amps at any given time. Even that may be high, I was imagining peak load time would likely be if an AC is running while I'm using a welder. Other than that it would be 1 or 2 woodworking tools being us at the same time and maybe a split AC unit if I put one in eventually.

Also - I remeasured the distance and the run will actually be 250'

Looking at Southwire's Voltage Drop Calc it looks like 80amps is within the limits of 2/0 AL for that run.

So - I think what I need is:
2/0, 2/0, 2/0, #6 wires with an 80 Amp (2-Pole) Breaker

Sound reasonable/logical?

appreciate the help

the online calculators are notoriously wrong. (for southwires i wonder why )... i posted the equation in the FAQs if you want to calc it yourself and possibly save some money on wire... im too lazy to calc it right now... also need to run out the door...

 

[dave*99]

It becomes a notable selling point vs. just having to spend a lot of $$ to properly protect the 200A SE cable and meter that gets no mention. Two panels fed off of a 320A meter pan with dual lugs is easier to install.

The selling point factor was also behind my earlier comment in post #7

Selling point math is different than a load calc.

 

[Innovate1]

1/0 at 250 ft and 80A give 3.33% voltage drop. Close enough on voltage drop I say. 100A is really big for a shop unless you have some really big equipment and/or multiple people working. You could downsize the neutral but some areas don't allow that.

320A service is very common in this area too and most homes have gas heat. Does make wiring a little less crowded in the panels with two 200s.

 

[alfredeneuman]

the online calculators are notoriously wrong. (for southwires i wonder why )

Southwire sells what the name implies... wire. It's based on a conductor temp of 60C.
I've found this one>>>>> https://www.calculator.net/voltage-drop-calculator.html to be fairly accurate.

 

[Kezorm]

Southwire calculator is fine, just select appropriate temperature.

 

[mm08822]

Southwire sells what the name implies... wire. It's based on a conductor temp of 60C.
I've found this one>>>>> https://www.calculator.net/voltage-drop-calculator.html to be fairly accurate.

The app has been upgraded to allow to insulation temp selection. BTW, before this change was done, the app had technical notes indicating they were using 60C ampacities for #1 and smaller b/c of NM-B.

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What is the correct way to size wire for a feed to a garage? My feed is about 75 feet. The Southwire voltage drop calculator says to use 1/0 for aluminum or 1 AWG for copper at 100 amps no matter if I put in 1 foot or 75 feet. Ampacity charts for 100 amps show copper should be 3 AWG and...

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