Wire/Conduit size

[Yookdew]

I am working on figuring out what I need to run a 100 amp subpanel in my detached garage. I'm looking for any advice on my current plan and whether or not I need to change anything.

The total length of the run between the main panel and the sub-panel is approximately 185 feet.

I am planning on coming out of the main panel and running approximately 70 feet under the house using SER cable to a junction box on the inside of the block foundation. In the junction box, I would transfer to MHF and run it in conduit underground approximately 115 feet to the detached garage.

Using the southwire calculator, it says for 100 amp at 185 feet I need 2/0 aluminum wire. I was looking at using 2/0-2/0-2/0-1 SER https://www.wireandcableyourway.com/2-0-3-1-ground-ser-aluminum-building-wire and 2/0-2/0-1-4 MHF https://www.wireandcableyourway.com/2-0-2-0-1-4-aluminum-mobile-home-feeder-cable .

Would this wire be the correct size with the smaller neutral and ground? Is there a different type of wire that would work better in my situation?

Also, would 2" conduit be big enough or do I need to go larger?

Thanks for any advice.

 

[mm08822]

1) What loads do you plan to run simultaneously? How do you figure 100A?
2) I would forget the ser, j-box and splices. Run 1.5" the entire way. Provide LB at entrance into foundation and pull in both directions from it.
3) I would not use MHF due to the twist it has. Use individual XHHW AL conductors. They layout nicely w/o extra bulk due to a twist.

 

[Innovate1]

#1 AL give me 3.8% voltage drop at 100A. I think I would be happy with that. Unless you have a couple people working and even then you may be hard pressed to come close to 100A. Some places don't allow a reduced neutral but otherwise that's not a problem - that's what I did here.

 

[Jimmyrace]

#1 AL give me 3.8% voltage drop at 100A. I think I would be happy with that. Unless you have a couple people working and even then you may be hard pressed to come close to 100A. Some places don't allow a reduced neutral but otherwise that's not a problem - that's what I did here.

3.8% is too much - most power co.'s want no less than 2.5% ... #1 cu would do it tho using the quick rule of one size up per 100 ft.

 

[Innovate1]

3.8% is too much - most power co.'s want no less than 2.5% ... #1 cu would do it tho using the quick rule of one size up per 100 ft.

The power company doesn't have any say in this - it's an existing service. The AHJ might though. Anyone who uses copper here has more money than sense.

 

[Sumboodie]

#2 aluminum SE is standard here. Most residental service is 100 amp

 

[Sumboodie]

3.8% is too much - most power co.'s want no less than 2.5% ... #1 cu would do it tho using the quick rule of one size up per 100 ft.

5% is usually max.

 

[PCustoms]

3.8% is too much - most power co.'s want no less than 2.5%

Got a code citation for that, or more made up information?

 

[Innovate1]

#2 aluminum SE is standard here. Most residental service is 100 amp

#2 AL is good for 100A for main feed but not for subpanel feed. It's good for 90A as subpanel feed and that's likely plenty for most garages but with the extra length you need to bump up the size for voltage drop. Or drop the breaker size to something like 80A which likely is still plenty.

 

[wyliesdiesels]

3.8% is too much - most power co.'s want no less than 2.5% ... #1 cu would do it tho using the quick rule of one size up per 100 ft.

what? the PoCo has no say in this whatsoever and the NEC doesnt have a code on it either, only suggestion.

 

[wyliesdiesels]

5% is usually max.

suggested max

 

[Yookdew]

A little more info that may help after reading the comments.

100 amp service is overkill for what I need right now but I would rather have excess and not have to worry about upgrading in the future if I add more load.

I will be the only one using the garage so there won't be any large simultaneous loads. The largest loads would be occasional welding and a smaller air compressor rated to draw 15 amps max. I will also be installing a mini-split in the future but those are typically a fairly low draw also.

I'm definitely wanting to stay with aluminum wire if possible since copper is so expensive. My reasoning with using SER under the house was because i could easily run it diagonally to where it will exit the foundation which would make a shorter run and I wouldn't have the expense of running extra conduit under the house. If I go with different wire that has to be in conduit under the house, I would have to route it differently and it would probably add 20-25 extra feet of wire.

Thanks for all of the help so far!

 

[PCustoms]

Are you drilling joists for SER, or surface mounting?

 

[Yookdew]

Are you drilling joists for SER, or surface mounting?

I was planning on surface mounting.

 

[PCustoms]

I was planning on surface mounting.

Then why can't you run the conduit along the same path?

I looked into similar before, and by the time I bought a box and connectors is was cheaper/easier to run PVC the whole way

 

[mike93lx]

A little more info that may help after reading the comments.

100 amp service is overkill for what I need right now but I would rather have excess and not have to worry about upgrading in the future if I add more load.

I will be the only one using the garage so there won't be any large simultaneous loads. The largest loads would be occasional welding and a smaller air compressor rated to draw 15 amps max. I will also be installing a mini-split in the future but those are typically a fairly low draw also.

I'm definitely wanting to stay with aluminum wire if possible since copper is so expensive. My reasoning with using SER under the house was because i could easily run it diagonally to where it will exit the foundation which would make a shorter run and I wouldn't have the expense of running extra conduit under the house. If I go with different wire that has to be in conduit under the house, I would have to route it differently and it would probably add 20-25 extra feet of wire.

Thanks for all of the help so far!

In a single person shop, adding equipment doesn't really add load. You can only use so much at one time, with max likely being a big hvac system running while you are plasma cutting.

What ifs are the most expensive upgrades

 

[mm08822]

A little more info that may help after reading the comments.

100 amp service is overkill for what I need right now but I would rather have excess and not have to worry about upgrading in the future if I add more load.

I will be the only one using the garage so there won't be any large simultaneous loads. The largest loads would be occasional welding and a smaller air compressor rated to draw 15 amps max. I will also be installing a mini-split in the future but those are typically a fairly low draw also.

I'm definitely wanting to stay with aluminum wire if possible since copper is so expensive. My reasoning with using SER under the house was because i could easily run it diagonally to where it will exit the foundation which would make a shorter run and I wouldn't have the expense of running extra conduit under the house. If I go with different wire that has to be in conduit under the house, I would have to route it differently and it would probably add 20-25 extra feet of wire.

Thanks for all of the help so far!

20-25' of conduit/conductor is offset by the elimination of jbox and splicing. Running conduit on the undeside of joists is easy.

 

[Yookdew]

So it sounds like doing a continuous run in conduit using aluminum XHHW is the best plan.

What size wire and conduit would be acceptable? I see the mention of #1 and #2 in this post. When i use the southwire calculator it is coming up with 2/0 with a 2.74% voltage drop.

 

[mike93lx]

So it sounds like doing a continuous run in conduit using aluminum XHHW is the best plan.

What size wire and conduit would be acceptable? I see the mention of #1 and #2 in this post. When i use the southwire calculator it is coming up with 2/0 with a 2.74% voltage drop.

Part of the issue is differing opinions on what is needed for load and what voltage drop is acceptable. If that 100a is really important, I'd do 1/0 and 1.5" conduit. Probably two 1/0's, a 1 and a 4

 

[Innovate1]

So it sounds like doing a continuous run in conduit using aluminum XHHW is the best plan.

What size wire and conduit would be acceptable? I see the mention of #1 and #2 in this post. When i use the southwire calculator it is coming up with 2/0 with a 2.74% voltage drop.

That's because the default voltage drop is 3%. Change the 3% up a bit and the wire size goes down. You may also be limited by the default "residential" selection near the top. Change that to Commercial 70C as I think all the terminal devices are rated for that. If I do that and enter 80A I get 3.78% voltage drop for #2 AL. Think that's what I would do. Although going to 2/0 wire is only about $200 more so not too bad if you really want/need 100A with minimal drop. The subpanel can be a 100A main with either wire/breaker feed as that breaker is just a shutoff and not protecting the feed wire.

 

[Yookdew]

That's because the default voltage drop is 3%. Change the 3% up a bit and the wire size goes down. You may also be limited by the default "residential" selection near the top. Change that to Commercial 70C as I think all the terminal devices are rated for that. If I do that and enter 80A I get 3.78% voltage drop for #2 AL. Think that's what I would do. Although going to 2/0 wire is only about $200 more so not too bad if you really want/need 100A with minimal drop. The subpanel can be a 100A main with either wire/breaker feed as that breaker is just a shutoff and not protecting the feed wire.

So if I go with 80A and #2 AL, what size conduit would you recommend?

Also, would I need a #2 ground or would it be downsized?

 

[wyliesdiesels]

#6 AL ground is fine

 

[Yookdew]

So I think I have my final plan.

It's not much more money to stick with 100 amp so I am looking at 3 XHHW 1/0 conductors with a #4 ground run in continuous conduit.

Is 1.5" conduit big enough or would you step it up to 2". Using the southwire conduit fill calculator it says 1.5" has a low probability for a jam but I would like some real world advice.

If any of this looks like it won't work, I'm open to suggestions.

 

[75gmck25]

I'd run 2", and keep close track of the orientation of the junctions in the conduit. You want to pull the wire against the smooth side of the transition, and avoid pulling up against the lip/joint where it connects the next section of conduit. It makes a big difference when you are pulling this size wire bundle for 70 feet.