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How Many 20 Amp Single Phase Circuits?

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Forum topic by Steinbierz posted 09-29-2020 06:48 PM 377 views 0 times favorited 9 replies Add to Favorites Watch
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Steinbierz

137 posts in 1019 days


09-29-2020 06:48 PM

Hello,

I have mentioned on several other threads of the 1500 sq. ft. wood shop I am currently putting together for a small family business. I have 400 amp separate service ran to the building and the majority of my machinery (sliding table saw, bandsaw, jointer/planer, DC, air compressor) is three-phase through a Phase Perfect. I will also have some single-phase 240v circuits e.g. lathe. My question is to those of you who have similar size shops, whether for hobby or business, how many separate circuits did you run around the shop for 15/20 amp service (I am running all 20 amp)? BTW, the majority of the time there will be no more than two people working in the shop…very rarely three.

I have more circuit panels with more spots for circuits than I will ever use (40 circuit main panel and two 20 circuit sub panels). The sub panels are on different walls for better circuit distribution. It becomes very easy to get in the mind set that, other than the cost of copper and breakers, to run a bunch of circuits (even if spares are tucked away in a junction box). What hits home is that for every one of those circuits, you also have to add the cost of having them GFCI protected. So, even if you think you might someday need extra circuits in the ceiling, as an example, they will have to be GFCI and, unless your power runs through a wall GFCI receptacle first, you would need to install a GFCI breaker (not cheap). This really has me reevaluating what is adequate versus every corded drill or sander having its own dedicated outlet! ;) Thanks.

-- Larry ~ Alvin, TX (Home of Nolan Ryan)


9 replies so far

View CaptainKlutz's profile

CaptainKlutz

3722 posts in 2377 days


#1 posted 09-30-2020 11:49 AM

IME – The answer to this depends on how many work stations, using 120v tools, will be used at same time?

I use the same rule of thumb at home, that I used designing work stations in manufacturing plants:
Two 20A circuits, one at each end/side of a work bench (~4-6 ft a part depending on size of work area).
This allows the shop vac to be used at bench with router/sander, each on different circuit; and not have to worry if there is battery charger or task light at bench too. It also keeps cord lengths short, and avoid extension cords.

At home usually alternate & daisy chain circuits along same wall, so that 2 circuits can support 4 outlets for three work benches along 24ft of wall space (length of typical garage wall).
Never needed more than two 120V 20A circuits at one bench, unless there was major power tool sitting next to bench. I.E. If you plan to use a 120V drill press or mortiser next to a work bench, would install a dedicated outlet for tool as it becomes a separate workstation from the bench.

If you will have someone working at multiple work stations on same wall, then would install 2 circuits for each work area; unless swarf collection is always handled via central system.

Some folks recommend putting duplex box with 4 outlets with same 6 foot spacing. I find the resulting spaghetti hanging from wall problematic at work bench heights. I prefer to install a power strip on underside of bench for power tools, and another up under a shelf over the bench for the battery chargers; which means only 2 plugs at wall?
Even when I have 3 ROS sanders with different grits at one bench, all are plugged into power strip out of way, and a single person only uses one at time.

At industrial work stations we didn’t use standard wall outlets, or surge strips. We used Wiremold/Plugmold products to add strips of outlets . Would isolate the center of strip and feed the Wiremold strip from both ends with different circuits when needed more power at one station. Having the strip run the entire length of bench made wires more manageable.

YMMV, and Best Luck.

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

View Fred Hargis's profile

Fred Hargis

6502 posts in 3376 days


#2 posted 09-30-2020 12:09 PM

To me the ideal setup is a 2 gang box every 63”’ along the wall placed 52” above the floor. Each of these will have 2 duplex outlets (commercial grade 20 amp). this spacing puts on on every 5th stud. Then in between each is a single gang box with a 240V outlet. In your case, the 3 phase outlets need to be figured in there somehow, but you get the drift. Now, ideally the 2 gang 120V boxes will have a separate wired into each duplex, that allows you 2 tools at each junction without worrying about tripping a breaker. I did that in my last shop, and the wiring was fairly labor intensive and used a lot more wire. In the current shop (1600 sq. ft total) I still did that outlet layout but just a single circuit to the 2 120V boxes. I did put a 2 gang under the 2 windows and put a 120V duplex on one side, and a 20 amp 240V on the other (yes, you can get plates for that arrangement. You can see in the photo I also put some hear the ceiling as well as in the ceiling. As for number of circuits, I have each wall on it’s own breaker to keep things simple. The ceiling outlets are a bit of a mix, but the lights are on a dedicated circuit.

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

View GrantA's profile

GrantA

2894 posts in 2290 days


#3 posted 09-30-2020 01:20 PM

OK I see now we’re just talking about the 120v circuits, yes technically they do need to be GFCI protected.
Any machine in my shop that needs a 20a or bigger circuit gets a dedicated circuit. Unless you’re just out of panel space there’s no sense trying to run multiple machines off one circuit that could overload the circuit. Even if you say they’ll never be on at the same time.
As for small tool circuits I like to run 2 circuits down a wall alternating receptacles. Power strips are the way to go for things like sanders and drills.

View Steinbierz's profile

Steinbierz

137 posts in 1019 days


#4 posted 09-30-2020 02:57 PM



IME – The answer to this depends on how many work stations, using 120v tools, will be used at same time?

I use the same rule of thumb at home, that I used designing work stations in manufacturing plants:
Two 20A circuits, one at each end/side of a work bench (~4-6 ft a part depending on size of work area).
This allows the shop vac to be used at bench with router/sander, each on different circuit; and not have to worry if there is battery charger or task light at bench too. It also keeps cord lengths short, and avoid extension cords.

At home usually alternate & daisy chain circuits along same wall, so that 2 circuits can support 4 outlets for three work benches along 24ft of wall space (length of typical garage wall).
Never needed more than two 120V 20A circuits at one bench, unless there was major power tool sitting next to bench. I.E. If you plan to use a 120V drill press or mortiser next to a work bench, would install a dedicated outlet for tool as it becomes a separate workstation from the bench.

If you will have someone working at multiple work stations on same wall, then would install 2 circuits for each work area; unless swarf collection is always handled via central system.

Some folks recommend putting duplex box with 4 outlets with same 6 foot spacing. I find the resulting spaghetti hanging from wall problematic at work bench heights. I prefer to install a power strip on underside of bench for power tools, and another up under a shelf over the bench for the battery chargers; which means only 2 plugs at wall?
Even when I have 3 ROS sanders with different grits at one bench, all are plugged into power strip out of way, and a single person only uses one at time.

At industrial work stations we didn t use standard wall outlets, or surge strips. We used Wiremold/Plugmold products to add strips of outlets . Would isolate the center of strip and feed the Wiremold strip from both ends with different circuits when needed more power at one station. Having the strip run the entire length of bench made wires more manageable.

YMMV, and Best Luck.

- CaptainKlutz

Thank you for the outstanding answer to a question that really is a personal situation with no two shops really being the same. I also realized that I hadn’t finished a sentence I had started in my OP stating that there would seldom be more than two people working in the shop at a time.

I have already ran conduit in part of my shop with duplex boxes and four outlets in each with a separate circuit feeding every other box. As I work around to the other side of the shop that is divided (not quite evenly) by two large bay doors I am going to be coming off of other sub panels for the 120V circuits. I felt like I didn’t really need more than two separate circuits at a work bench, which panel I pulled them off of would be dictated by the location of them. Your answer has confirmed that for the general wall outlets. I am going to take your advice and look at how I can incorporate power strips on the underside of my benches. Are there any that you have used in the past that were chosen due to the nature of the work or was it what you could find at a big box store? Thanks.

-- Larry ~ Alvin, TX (Home of Nolan Ryan)

View Steinbierz's profile

Steinbierz

137 posts in 1019 days


#5 posted 09-30-2020 03:08 PM


To me the ideal setup is a 2 gang box every 63” along the wall placed 52” above the floor. Each of these will have 2 duplex outlets (commercial grade 20 amp). this spacing puts on on every 5th stud. Then in between each is a single gang box with a 240V outlet. In your case, the 3 phase outlets need to be figured in there somehow, but you get the drift. Now, ideally the 2 gang 120V boxes will have a separate wired into each duplex, that allows you 2 tools at each junction without worrying about tripping a breaker. I did that in my last shop, and the wiring was fairly labor intensive and used a lot more wire. In the current shop (1600 sq. ft total) I still did that outlet layout but just a single circuit to the 2 120V boxes. I did put a 2 gang under the 2 windows and put a 120V duplex on one side, and a 20 amp 240V on the other (yes, you can get plates for that arrangement. You can see in the photo I also put some hear the ceiling as well as in the ceiling. As for number of circuits, I have each wall on it s own breaker to keep things simple. The ceiling outlets are a bit of a mix, but the lights are on a dedicated circuit.

- Fred Hargis

Thanks Fred. I am pretty much running my conduit and wiring the boxes as you describe above (alternating boxes on a different circuit) although my box separation might be a little different depending on the wall I am working with. I had really thought about splitting the boxes so that each box had two circuits rather than every other box but decided not to based on the complexity of the wiring. I still may do that along one of my walls…have to put some more thought into keeping it consistent throughout the building though.

As far as my three-phase, I for the most part have all of that figured out. The only thing that is still in question is whether or not I am going to enclose a 10’ x 25’ lean-to so that I can move my DC and air compressor out there to free up some space in the building. I am leaning heavily in that direction but just coming off of major back surgery, that is something that I am not able to tackle at the moment.

BTW…looks like you have a very nice space for a workshop!

-- Larry ~ Alvin, TX (Home of Nolan Ryan)

View Steinbierz's profile

Steinbierz

137 posts in 1019 days


#6 posted 09-30-2020 03:12 PM


OK I see now we re just talking about the 120v circuits, yes technically they do need to be GFCI protected.
Any machine in my shop that needs a 20a or bigger circuit gets a dedicated circuit. Unless you re just out of panel space there s no sense trying to run multiple machines off one circuit that could overload the circuit. Even if you say they ll never be on at the same time.
As for small tool circuits I like to run 2 circuits down a wall alternating receptacles. Power strips are the way to go for things like sanders and drills.

- GrantA

Thanks Grant. Several mentions of power strips now so I am going to have to incorporate that into my thinking and layout.

-- Larry ~ Alvin, TX (Home of Nolan Ryan)

View clagwell's profile

clagwell

312 posts in 675 days


#7 posted 09-30-2020 04:56 PM



Thanks Grant. Several mentions of power strips now so I am going to have to incorporate that into my thinking and layout.

- Steinbierz

When you’re looking at power strips be sure to consider Plugmold strips. They’re available in various sizes and receptacle spacing. Some models also include alternating circuits. They are permanently installed, unlike power strips. Not cheap however.

-- Dave, Tippecanoe County, IN --- Is there a corollary to Beranek.s Law that applies to dust collection?

View Steinbierz's profile

Steinbierz

137 posts in 1019 days


#8 posted 09-30-2020 05:07 PM


Thanks Grant. Several mentions of power strips now so I am going to have to incorporate that into my thinking and layout.

- Steinbierz

When you re looking at power strips be sure to consider Plugmold strips. They re available in various sizes and receptacle spacing. Some models also include alternating circuits. They are permanently installed, unlike power strips. Not cheap however.

- clagwell

Thanks for the recommendation. This is one item that I have never used so have zero experience with it. I’ll have to research what the available options for Plugmold is as it could address a few layout issues I am still contemplating.

-- Larry ~ Alvin, TX (Home of Nolan Ryan)

View CaptainKlutz's profile

CaptainKlutz

3722 posts in 2377 days


#9 posted 09-30-2020 10:36 PM

FWIW – Plugmold is trade mark by Legrand
https://legrand.webdamdb.com/directdownload.php?ti=38639283&tok=zAFbjUwb06tMKpHcprY95QRR

Plugmold/wiremold is listed under surface mounted raceway. Often called decorative conduit for office/lab areas?

Your local industrial electrical supply should have basic components in stock. There are a massive number of options available via custom order.
Here is one online store link from Graybar that might have local branch in your area?
https://www.graybar.com/store/en/gb/conduit-raceway-and-cable-support/surface-mounted-raceways-and-fittings/surface-mounted-raceways?

Grainger carries some wiremold parts too, but tends to be more expensive IME.

Best Luck.

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

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