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Subpanel for Two Car Garage Workspace

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Forum topic by Autorotate posted 11-13-2018 04:18 PM 563 views 0 times favorited 18 replies Add to Favorites Watch
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Autorotate

40 posts in 1118 days


11-13-2018 04:18 PM

Topic tags/keywords: electric shop subpanel circuit 240

Hello,

I am interested in installing a subpanel to my attached two car garage. A few years back I ran (1) 240 line dedicated to my Tablesaw, (1) 20 amp 120 line for my dust extractor, and (1) miscellaneous 20 amp all on their own circuits. However, I am looking to add a ceiling heater as well as a few other tools in the future (See pic attached with all amperage) and only have 5 open slots on my main 200 amp service. I am running out of room quickly, and with a basement refinish next year, would like to keep those free.

I have about a 50-60 foot run from the basement to the garage. So I know I am going to need some heavy wire probably 3 gauge or 1/0.

My questions are:

- Would you recommend an 80 amp panel?

- Should I remove the (3) “Garage” circuits and transition them from the new subpanel?

- Any other specifics I should take into consideration so I only have to do this one last time?

I know that I will only be able to run two of the bigger items at once. This will mean shutting off the heater if the tablesaw and dust extractor are on.

I wanted to see some opinions on how others have done it. Thanks!


18 replies so far

View GrantA's profile (online now)

GrantA

691 posts in 1606 days


#1 posted 11-13-2018 04:32 PM

Where are you getting the heater specs? I have the 5000w (17,000BTU) unit and it’s on a 30a circuit, I just pulled up the specs and it calls for 20.9a

Aside from that, it looks like you’re serious enough to call the power company and see about upgrading to 400a service!

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jamsomito

304 posts in 625 days


#2 posted 11-13-2018 04:39 PM

I’m looking to add a subpanel to my 2 car garage shop also, but I only have 1×15A circuit now (highly inadequate). I was looking at only 50A for the panel because I could stay with 6ga feeder to save cost. The wire is the biggest expense for me. This would allow me one 20A 240v circuit for big tools (only running one at a time), and 4×20A 120v circuits I can use for 1) dust collector, 2) plug load tools 3) IR heater, 3) air cleaner and 4) misc garage items (fridge, charging the kids electric car, etc). Eventually I plan to convert one or two of those 120v circuits into another 240v circuit for a bigger dust collector, and it will be doable but tight.

I don’t foresee needing much more than 50A for myself but the extra headroom would be nice for hassle-free future expansion. Plus if you sell the house you could pitch it as “electric car charging ready” – I don’t think 50A is quite enough for that.

I don’t think I would tear out or relocate your existing runs from the main panel though. It seems like a lot of work just to tidy things up.

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Autorotate

40 posts in 1118 days


#3 posted 11-13-2018 04:47 PM

Thank you both very much for the responses. And I completely agree that I think 50-60A would be more than sufficient, but I may just add the 80A for peace of mind. I may leave (1) 20A for the dust extractor on the main and eliminate the (1) 240, and (1) 20 amp extra just to free some space. It should not be that big of deal since it is in an unfinished basement.

Ultimately, I do not have workers or a business so no more than two items will be running at once. I just have to add up the rest of my house since I am all electric. But 200 amp is more than enough since everything is energy efficient and LED these days.

As far as the specs for the heater… 31.3 at the 7500 watt setting. It is the 20.9A at the 5000 just like you said.

https://www.northerntool.com/images/downloads/manuals/44740.pdf

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bmerrill

26 posts in 272 days


#4 posted 11-13-2018 04:53 PM

Installing an 80-100 amp 20-30 space sub-panel in the garage and feeding it from the main panel would be the first thought.
Have you considered a Mini-Split for heating and cooling. They are very efficient. A 2 ton unit runs off on 1 20AMP 240 breaker.

-- "Do. Or do not. There is no try". Yoda

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GrantA

691 posts in 1606 days


#5 posted 11-13-2018 05:11 PM

Autorotate I don’t see your location listed but as bmerril just said think about AC, lighting, air compressor, refrigerator. These don’t use much constantly but when they cycle (not the lights), breakers can trip. If you have a well, the well pump uses a LOT when it starts up, water heater too. Even knowing only 2 tools will be used at once, if you are taking a heavy cut with the tablesaw, with the DC running, lights on, etc then a fridge cycles, it may trip a breaker. Laundry running in the house too while you’re running the shop. Just food for thought.

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smitdog

410 posts in 2304 days


#6 posted 11-13-2018 05:12 PM

If I were you I’d just go with a Main Lug load center (no main breaker) for the garage. Put a 100 amp 220 breaker in your main box and run the code required gauge for 100 amp over the 50 ft run to the garage lug. The lug in the garage doesn’t need a main breaker since you have the 100 amp breaker in your main panel in the house already. Then you run all your different circuits (including the separate ones running to the house now) in the garage from the lug. 100 amp would power everything you have since it’s not like you are running everything all at once. Even if you take your highest listed combo all at once, 26 amp drum sander, 45 amp heater and 20 amp dust collector, you are only at 91 amps (they won’t even use that much amperage while running anyway, probably closer to half of that total). Even counting lights and other miscellaneous stuff 100 amps will be plenty.

You could definitely go with a smaller breaker in the main panel and smaller gauge wire out to the garage to save on cost too.

-- Jarrett - Mount Vernon, Ohio

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Fred Hargis

5173 posts in 2692 days


#7 posted 11-13-2018 06:49 PM

I’m in my third detached shop, and have had a 100 amp subpanel in each. It’s more than needed, I could have probably done just as well with 60 amps. The thing is, when I was pricing the stuff, it really wasn’t much more expensive to run 100 versus anything less….and the 100 gives you the spare capacity if it’s ever needed (by you or a subsequent owner). If you’re doing it yourself, I’d price the stuff out ans see what the cost is; then go from there.

-- Our village hasn't lost it's idiot, he was elected to congress.

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CaptainKlutz

598 posts in 1693 days


#8 posted 11-13-2018 07:17 PM

IMHO – You have already proven that your workshop needs are never truly known in beginning and constantly change.
Best solution is to add sub-panel that allows expansion.
If you need the space in main panel, then move existing circuits to sub-panel, if not leave them alone. There is no reason to waste time and copper wire, re-running those circuits. Solid copper building wire does not like to be reused, and can develop stress fractures on second installation, due damage during 1st install.

Notes:
- If you chose to run a sub-panel larger than 60A, make sure to check the specs on your main panel. Most of the low cost residential panels have limitations on current draw based on location of breaker slot. As example, Square D Homeline requires any breaker over 60A to be in 1st 4 slots on top.

- NEC code also recommends a maximum sub-panel circuit limit for 50% of main panel, but many local codes allow 125A sub panel from 200A main, provided the total panel load can is below rated max. Most panel mfg sell 125A residential breakers, but check your electrical codes before making the addition. These massive 125A breakers are usually required to be top most slots as well.

- Cost difference between a expandable main lug 60A & 100A panel is negligible, when compared to over all costs, or hassle of needing to upgrade the panel in another 5 years. Suggest a 20+ slot, 100A+ main lug sub panel, and feed it with what ever power you need. 50-60A will run most single user home workshops. Need 70-80A if you include HVAC equipment in shop. Smaller panel might save $20-30, but largest cost difference in a larger sub panel is size of wire feeding the panel, not hardware.
IMHO, best solution is to install 1/0-1/0-1/0-2 AL service wire between main and sub-panel (indoor install only) .vs #6 Cu (60A) for same cost, then you can handle 100A limit per NEC code and know you can use most anything in the sub panel, even if you only start with 50A breaker. (100A breaker is 5x cost of 50A)

YMMV

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

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ajshobby

102 posts in 2507 days


#9 posted 11-13-2018 08:32 PM

With electrical you can never go to big. Allowing room (for breakers) to expand is probably the best advice the electrician gave me when he installed my 120 amp panel in the garage at my old house. Had 26 open slots when installed. I was down to 6 open slots when i moved. At the new house I installed a 26 breaker 90amp panel for the garage. I have a basement wood shop so 90 amps was plenty for the garage and allows plenty of room for expansion.

AJ in Mpls

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mathguy1981

83 posts in 103 days


#10 posted 11-13-2018 08:57 PM

I recently did a 50Amp sub panel in my garage. I paid for the original house electrician from the builder to install it, so everything would match and be to code. Yes, could have done myself, but frankly didn’t want to.
I had them set up 1 240V 20AMP for the tablesaw and 3 individual lines 20Amp 120V for various machines. I have lots of room in the subpanel to add a second 240 or more 120 as I go…but enough for me.

Can you possibly get a smaller/more efficient heater? Sounds like that’s a huge issue for somewhere you won’t be most hours of the day….

-- Two thumbs and counting

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WhyMe

1073 posts in 1760 days


#11 posted 11-13-2018 10:20 PM



IMHO, best solution is to install 1/0-1/0-1/0-2 AL service wire between main and sub-panel (indoor install only) .vs #6 Cu (60A) for same cost, then you can handle 100A limit per NEC code and know you can use most anything in the sub panel, even if you only start with 50A breaker. (100A breaker is 5x cost of 50A)

YMMV

- CaptainKlutz

#1/0 Al is limited to 120A, where are you getting 100A limit per the NEC. If using 100A subpanel then #1-1-1-3 Al SER can be used for 100A.

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CaptainKlutz

598 posts in 1693 days


#12 posted 11-14-2018 12:34 AM


IMHO, best solution is to install 1/0-1/0-1/0-2 AL service wire between main and sub-panel (indoor install only) .vs #6 Cu (60A) for same cost, then you can handle 100A limit per NEC code and know you can use most anything in the sub panel, even if you only start with 50A breaker. (100A breaker is 5x cost of 50A)

YMMV
- CaptainKlutz

#1/0 Al is limited to 120A, where are you getting 100A limit per the NEC. If using 100A subpanel then #1-1-1-3 Al SER can be used for 100A.

- WhyMe

Why I recommend 1/0 AL SER triplex wire for 100A sub-panel question above?

Normally #1 SER wire is rated for 100A, BUT NEC requires use of 60F degree temperature ratings for occupied residential wiring (regardless of panel/junction rating), which lowers the rating on #1 to 85 amps.
It is one of those pesky footnotes often overlooked.
If don’t want to dig into NEC documents, here is PDF rating summary from USAWIRE that includes the note.
Basically, you can only use the 75F ratings for AL SER/URD wire if main/lateral feeder is external to building, or inside a raceway/conduit when inside a residence. Since running PVC conduit inside house walls/ceiling of house is costly, using 60F rating for AL wire is usually cheaper option – which delivers the 1/0 recommendation.

IMHO, if the above 100A sub-panel application was suitable for a conduit run and could use 75F temp ratings in residence, I would recommend #3 THHN copper conductors at a cost of ~ $3.5/ft for 3+gnd wires for 100A (#4 THHN for even cheaper 80A panel), even though AL 1/0 SER triplex is ~$2.50/ft. Call me old fashion, but I prefer using copper over AL wire unless the cost is significantly higher.

Electrical wiring requires professional(s) support. If any of the above discussion is not clear, call your local electrical inspector for clarification, or cruise over to Mike Holt web site for some education.

PS – Please ignore me, as I am not a qualified expert.
My background is about a dozen residential sub-panels installed over last 20 years, and 15+ years of managing commercial electrical equipment installations in factories. I always get a qualified professional review for any new installation.

Cheers!

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

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Autorotate

40 posts in 1118 days


#13 posted 11-14-2018 01:25 AM

Wow, I originally came on here for a few suggestions, and I am grateful I did. Thank you all very much for all the advice and it looks like the 100A is the way to go. Regardless if I do it or not, I will have a certified electrician look over what I am going to do even if I have to pay a few dollars for that.

The above comments definitely all make sense to me, but I am still not a certified electrician. I have ran most of the electric in my house, but always double check with the professionals.

I even thought of having the electric company just branch me off a new 100A service line dedicated just for the garage. I am just not sure if that would be cost efficient. I can say that having an entire house of “all electric” is a little annoying. I wish the bigger appliances were on some type of gas. But that’s an entirely different story.

Thanks again everyone I really appreciate it!

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GrantA

691 posts in 1606 days


#14 posted 11-14-2018 02:29 AM

You wouldn’t want a separate meter as it’ll carry a minimum monthly charge, you might be surprised how affordable upgrading the service is though, have an electrician check it out. I have 400a service with 2 200a panels next to the meter base. One feeds my house panel and the other feeds a 150a panel in my shop. My well is by the shop so yeah 100a would be good. I don’t have to play musical breakers though and that’s the goal! Good luck and let us know what you end up doing
We like pictures!

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Holbs

2004 posts in 2228 days


#15 posted 11-14-2018 03:18 PM

For safety, keep your existing main house panel lighting in play even if it’s a single light bulb. I was in the same boat as you and am very happy with the end results. It is nice to have safety lighting off your main panel incase your subpanel throws a breaker at 9pm while you are running a table saw.
http://lumberjocks.com/Holbs/blog/34833

-- The Carpenter Bee is derived from the Ancient Greek word wood-cutter "xylokopos/ξυλοκὀπος"

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