Detached Garage 90A or 100A Subpanel

[nouveauree]

This is a post similar to others...but taking a slightly different spin. I want to run a 100A SubPanel to a new detached garage.

1. From 200A Main Panel to 12x12 Junction Box where the LB enters the garage is 45' run through the attic, all inside the current garage.
2. From 12x12 Junction Box through LB through 1 1/2" buried PVC conduit to LB at new garage is ~50 feet that will be long enough to get to subpanel inside new garage.

My plan is to run SER from Main panel to junction box, and then USE-2 or URD stranded from junction box to new garage. For 100A, I need 3-3-3-5 copper or 1-1-1-3 aluminum (all terminations are rated 75C). Copper is very expensive...so going to use aluminum. Problem is that 2-2-2-4 AL is very easy to get, 1-1-1-3 AL not as easy.

So, if I have all my info above correctly, the question is what do I lose dropping to a 90A panel verse 100A. Garage is large 30x40 with upstairs storage. Other than basic electrical (lighting and outlets), I will have a 220V radial arm saw and a 220V air compressor.

And finally, do I need one or two grounding rods, and what size CU conductor from grounding rod to panel?

Thoughts? Guidance and advice greatly appreciated.

Thank you.
Nouveauree

 

[u2slow]

When you push the capacity of a conductor, you incur more heat and voltage-drop. #2 alum is rated for 90A.

If you feel you need more, you can look for #0 or #00 (aka #1/0 or #2/0) alum. Your 200A panel can probably take a 125A breaker.

The actual amperage of the saw and welder would help. Are you planning on any electric heat/AC, etc?

 

[jmdirk]

I just did a 100A sub-panel in my new garage. #0 AL wire. Probably 50ft from the main panel.

If all you really have for high demand is a radial arm saw and air compressor, you probably already have more than sufficient capacity with 90A. My 60 gallon, 3HP compressor is only 240V/15A.

 

[nadogail]

For the loads you mentioned 90 Amps should be more than adequate.

 

[Innovate1]

You need two grounds rods for a subpanel in a detached building. Doesn't depend on the amperage of the panel. I don't recall the size needed for that wire.

#1 Aluminum is easy to get. I ordered my spools of XHHW from wireandcablemyway.com. No connection other than a happy customer. They will cut to length and put on individual spools as you specify so it is easy to pull. But I agree with others that 90A is sufficient for what you are describing. 60A sounds like it would be plenty.

You don't show a location. These answers are for USA locations.

 

[exranger06]

You don't need a "90A subpanel." You can still use a 100A subpanel with #2 Al, BUT the breaker in the main panel that feeds it must be a 90A breaker.

 

[OccupantRJ]

My shop is run on 60 amps, and I have a heat pump, 5 hp compressor,lathe, mill, etc, and no problems running it as a one man shop. I did cut the heat pump strips back to 5,000 watts.

 

[pattenp]

Use bare solid #6 Cu for the electrode ground conductor. That will cover you up to 200A. The bare #6Cu solid is fairly common at the big box stores. #8 Cu is for up to 100A.

 

[wyliesdiesels]

FIY- URD is not allowed inside the structure

If you can run conduit panel to panel, then i would just use #2 MHF all the way...

 

[Terry D]

As already said the easiest and cheapest route would be to put in a 100 amp main breaker at the garage. The main breaker would be your disconnecting means. You would size the breaker in your main panel feeding the sub to what size wire you use . At that distance, I would not be concerned about voltage drop

 

[PoorUB]

I also have just a 60 amp panel in my garage with a 5HP compressor and some other loads that are not as high, no issues.

 

[alfredeneuman]

The bare #6Cu solid is fairly common at the big box stores. #8 Cu is for up to 100A.

....and #6 is the minimum size you can run without conduit (It's required for #8).

 

[nouveauree]

....and #6 is the minimum size you can run without conduit (It's required for #8).

Thank you very much.

 

[nouveauree]

This is a post similar to others...but taking a slightly different spin. I want to run a 100A SubPanel to a new detached garage.

1. From 200A Main Panel to 12x12 Junction Box where the LB enters the garage is 45' run through the attic, all inside the current garage.
2. From 12x12 Junction Box through LB through 1 1/2" buried PVC conduit to LB at new garage is ~50 feet that will be long enough to get to subpanel inside new garage.

My plan is to run SER from Main panel to junction box, and then USE-2 or URD stranded from junction box to new garage. For 100A, I need 3-3-3-5 copper or 1-1-1-3 aluminum (all terminations are rated 75C). Copper is very expensive...so going to use aluminum. Problem is that 2-2-2-4 AL is very easy to get, 1-1-1-3 AL not as easy.

So, if I have all my info above correctly, the question is what do I lose dropping to a 90A panel verse 100A. Garage is large 30x40 with upstairs storage. Other than basic electrical (lighting and outlets), I will have a 220V radial arm saw and a 220V air compressor.

And finally, do I need one or two grounding rods, and what size CU conductor from grounding rod to panel?

Thoughts? Guidance and advice greatly appreciated.

Thank you.
Nouveauree

Thank you everyone. I appreciate all of your guidance.

I've decided to run 1-1-1-3 AL SER from the panel to the junction box. Then 1 AWG singled stranded (4 wires) from the junction box in the current building through the Conduit/LB/Junction/Conduit to the new panel in the garage. And will use 6 CU copper for the ground bars.

Thanks again...and comments/guidance is still appreciated.

 

[wyliesdiesels]

Thank you everyone. I appreciate all of your guidance.

I've decided to run 1-1-1-3 AL SER from the panel to the junction box. Then 1 AWG singled stranded (4 wires) from the junction box in the current building through the Conduit/LB/Junction/Conduit to the new panel in the garage. And will use 6 CU copper for the ground bars.

Thanks again...and comments/guidance is still appreciated.

The EGC doesnt need to be #1. you can run #6 AL for the EGC for 100a breaker but it would need to be green insulated. or go with #4 AL black and tape the ends...

 

[Kezorm]

Not saying this is necessarily a good idea because length of the run. But, as a feeder, #4 copper or #2 aluminum is good for 100A. See NEC 310.12. Personally, I would go up a size because 100' run (i.e. #1 aluminum as you are planning).

Move along, nothing to see here (see following post from wyliediesels)

 

[wyliesdiesels]

Not saying this is necessarily a good idea because length of the run. But, as a feeder, #4 copper or #2 aluminum is good for 100A. See NEC 310.12. Personally, I would go up a size because 100' run (i.e. #1 aluminum as you are planning).

Nope. Not for a feeder to a detached structure

 

[Kezorm]

@wyliesdiesels Got it. Thanks for the correction. Think I may have an incomplete understanding of 310.12. Good thing I always design by overkill (I sized my sub panel feeder per table 310.16).

 

[theoldwizard1]

The only purpose for the "main breaker" in a sub-panel is to disconnect all loads in that panel so you can work on them. The most important thing is the breaker in the main panel and the size of the cable feeding the sub-panel.

 

[Denwood]

Geez, I run a few 240V tools and charge an EV to boot on 30A@240V. When I'm working in the shop, the EV is not there, so I have lots of power.

You'll have miles to spare at 90A.

 

[schalliol]

It may seem silly to some, but can you upgrade to 400 at the house and drop in a 200 in the garage? That would afford room for tools, heating and multiple EVs if that's something you get into at some point. Usually the lines run to the meter are enough to do 400, and then you don't have to go into the house either.

 

[Innovate1]

It may seem silly to some, but can you upgrade to 400 at the house and drop in a 200 in the garage? That would afford room for tools, heating and multiple EVs if that's something you get into at some point. Usually the lines run to the meter are enough to do 400, and then you don't have to go into the house either.

Yes, that's silly given what the OP has posted about his needs.

 

[75gmck25]

90 amp breaker in the main panel and 2-2-2-4 AL MHF (or SER) to a 100 amp sub-panel is a common solution because all the pieces and parts are relatively cheap and easy to find.

Its very easy to go up (in amperage) from there, but you need to decide if you really need it. For example, if it costs you 20-30% more to get a full 100 amps, is it really worth it for 10 more amps?

 

[dcg9381]

So, if I have all my info above correctly, the question is what do I lose dropping to a 90A panel verse 100A. Garage is large 30x40 with upstairs storage. Other than basic electrical (lighting and outlets), I will have a 220V radial arm saw and a 220V air compressor.

It looks like they've discussed the particulars of wiring. For the less technical aspect to your question:

I feed a 2400 sqft shop on a 90A. 2 ACs, hot tub, we've got 240V wood tools, 240V welders, power a 1.5hp water pump, refrigerator. Even with a 5th wheel plugged in at full load, we've never had an issue tripping the main. I'm leaving out the "usual" loads like lighting, TVs, stereo, and the occasional rock band practice.

I'd reconsider if I was powering an electric tankless water heater or perhaps some major electrical resistance heater... Or 2 EVs.

Someone will scream "load calculator" - and that's probably right. But I can tell you that 90A has been covering us just fine..

The only question I'd have: Does the panel have enough breaker space?

If your 50' PVC is "straight enough" you could always do another pull another main in the future if you're able to pull more power than me...