I'm trying to decide what size circuits I should run in my new basement
(unfinished) shop. I just purchased a 3hp (18amp) table saw and a 2hp (12
amp) dust collector from Grizzly that both run on 220v. I plan to split
these out to 2 separate 20 amp circuits. I have a couple of questions:
1. Should I install GFCI outlets or breakers on either/both of these
2. Could I get by with a single 30 amp circuit?
3. I have plenty of room in my main panel but should I run a subpanel for
these circuits and future upgrades (florescent lights, more 110's) anyway?
You're better off using a 30A circuit for the table saw. It may even be
necessary; check the owner's manual for the saw's electrical requirements.
Code requires ground-fault protection on 120V outlets in basements, but AFAIK
it's optional for 240V circuits. It's not a bad idea anyway, though.
No. It's never a good idea to load a circuit at 100% of its rated capacity
(and it's a Code violation). You need two circuits.
Yes -- but the lighting circuit(s) should be supplied from your main panel,
not from the subpanel.
a) Provides a single point for disconnecting power to all receptacles in the
shop in case of emergency (or to prevent kids from starting up power tools).
Lighting should be supplied from the main panel so that an overload on
the subpanel doesn't leave you in the dark.
b) Easier and cheaper to install new circuits in the shop: you don't have to
pull as much wire as far, if your starting point is already in the shop.
Doug Miller (alphageek at milmac dot com)
How come we choose from just two people to run for president and 50 for Miss America?
I'm far from being an expert and will read closely other more expert
opinions but lets see if I'm on the right track here or not.
I'd use just a breaker on seperate circuits w/ a subpanel.
You could however you may overload it if both tools are running at the
same time. Someone else may be in the shop with you doing their thing.
Since its unfinished, I'd run a sub panel. That way if you ever need to
power down everything in that area you can do so closeby and quickly.
Plus it lets you run numerous circuits for the shop, again all
controlled at one place, the sub panel.
I've a 12x16 external shop I ran a subpanel to. The 16' walls have 4
outlets each on their own 20a circuits. The 12' wall has 3 outlets on
its own 20a circuit. The 6 overhead 4' florescent fixtures have their
own circuit, 15a. I've a small pond w/ pump that I'll plug in this
summer and will add a GFI plug for it since its going outside the shop,
plus I might plug in other stuff outside - who knows. In my case there
will rarely be anyone else in there at the same time as I, however...
Bottom line I think everyone would agree with is, if its unfinished, now
is the time to plan for the future, plus 20%. You'll never have too
much power nor too many outlets so give yourself some room for expansion
later on while you can w/o tearing up the place.
Since you have lots of spaces in that panel, let me suggest the following:
Buy a full box of 10-3 /W/ ground Romex and use 2P-30A c'bkrs for all your
240V circuits. (Leave the neutral unconnected at the receptacle if
Run individual circuits for each tool.
Buy a full box of 12-2 /W/ ground Romex and use 1P-20A c'bkrs for all your
You save money on wire because you are buying full spools and the c'bkrs are
all the same price 60A and below with the obvious difference between 1P &
Can't use Romex? Then buy 500 ft spools of single strand and do the same
And yes, spent a few years in the electrical distribution business,
designing systems and selling equipment.
S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
One instance would be that some local codes frown on using romex in conduit,
and you may have to de-rate the ampacity of the circuit if you do use it in
However, the NEC makes a good case for protecting romex with conduit in a
hazardous environment (a shop should qualify), so it is one of those issues
where there may be no clear cut guidance and you have to go with how the
inspector feels that day.
In my neck of the woods, non-metallic sheathed cable HAS to be
installed either in an enclosed wall, or in conduit. It absolutely
*cannot* be installed on the surface of a garage wall or in an exposed
stud wall in a garage. I would (and did) go with THNN wire in surface
mounted conduit - easy to change, exactly to code. GFCIs are required
on all 110v branches, but not on 240s.
Been through this too many times ... it is specifically why I mentioned it
as an area to be aware of in answer to the question:
"I plan to use Romex- that's what the rest of my house is wired with, but
under what circumstances would I NOT be able to use Romex or a similar style
Romex in conduit is OK in this locale as long as it is protection for the
wiring, but NOT as a wiring system.
You gotta be aware of, and be careful with, the terminology that inspectors
will often use for "gotacha's" on a bad day.
Since all Romex since the late 80s has been 90c for derating that is not an
issue. I can't imagine what their justification for derating would be anyway or
what table they would use. The derating table is the same whether a group of
conductors is in a cable, a raceway or simply bundled together.
In places that don't allow cousin Billy Bob to make up the rules as they go it
is recognized that you can sleeve Romex in conduit for physical protection.
Usually that is required on unfinished walls up to 6'6" off the finished floor.
Generally based on percentage of conduit fill, with romex considered as a
single conductor for calculating same, EXCEPT in cases where the conduit is
used to protect exposed wiring.
I mentioned the issue SPECIFICALLY because it IS an issue that is not
clearcut and comes up all the time, so being on the lookout for it in shop
wiring plans is wise if you're doing the work yourself and having it
inspected, as the OP apparently is.
Pretty difficult to say it more clearly than that.
That's what I stated, which you left out. However, you can just about bet
that romex in conduit is non-code as a "wiring system" in _most_ parts of
the USofA. It certainly is my area.
Primary limitation of Romex is that it can not be run exposed. It has to be
run behind a wall as an example.
What you are and are not allowed to do is under control of local codes in
If you are going to have exposed studs in the garage, then it is conduit or
Same would apply to surface mounting over existing plaster board.
If you are going to cover the wall studs with plaster board after wiring,
then romex works.
S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
You have to add "where exposed to physical damage". When I was in Md it was
very common to see Romex on running boards in garages and basements. My area of
Florida intreprets that as exposed to physical damage if it is within 6'6" of
You're wise putting them on separate circuits. Use 10ga wire for both in
case you want/need to upgrade later.
Is the saw rated at 18amp at 120v? ... if so, 20A should be sufficient if
your're going to run it at 220v,.
However, if the 18A rating is at 220v for the saw, you need to go with 30A
for the table saw.
... if you run 10ga wire, you got it covered no matter what..
May want to make the Dust Collector 30 A from the get go in case you want to
upgrade it in the future.
Most codes don't require GFCI on "dedicated circuits" for a single tool, but
if your basement is damp, strongly consider it.
The DC has to run while other tools are on, so it is much better of on its
You may have plenty of room now, but things have a habit of filling up
quickly for a shop. A subpanel is nice to have, and safer cause you can cut
everything off in the shop with one switch, or two, for any number of
reasons. ... 60A Main Brkr in the subpanel and a 60 amp Brkr feeding the
subpanel from the main is what I've got ... works nicely.
You can never have enough circuits (it's kind of like clamps).
Make sure your machinery and your lighting are on separate circuits.
You will discover the wisdom of this the first time you trip a breaker
and you find yourself in a pitch-black room standing 2 feet away from a
3 HP saw blade that's slowly spinning down.
Putting the everything (except the lighting) on a sub-panel makes it
easy to power down the whole shop. A disconnect switch upstream of the
panel that you can padlock in the "off" position can give peace of mind
if you've got kids in the house.
Add up how much stuff you might have running at one time. The obvious
things are the 3HP saw and the 2HP DC. Right there that's 25 amps or so
(at 220). But, what else? What's the heat like in the basement in the
winter? Maybe one or more 1000/1500W electric heaters? Maybe a
dehumidifier or air-conditioner in the summer? In addition to the DC,
maybe a room air circulating dust filter?
You'll have your basic lighting on another circuit, but if you're like
me, you'll also have random additional task lighting plugged into
utility outlets. An air compressor? Tons of little stuff like fans,
radio, recharger for your cordless drill. I couldn't survive without my
electric pencil sharpener :-)
It all adds up. 30A @ 220V isn't sounding very big any more, is it?
220 v. GFCI's are very expensive (over $100 ea). I did not install
these in my shop. However, I did use them on each 120v circuit.
That should be plenty to run a total of 7 HP.
I would not install one, if the main is conveniently located and has
available room for expansion. I installed all my outlets at once
(and lots of them) because it made it much easier. Install more
receptacles than you think you will need. They install fast, cheap,
and easy once you get going. "Leap-frog" the circuit outlets for more
The saw is a potential problem, depending on how you intend to wire it
up. If you're running permanent wiring to it -- as opposed to a socket
that you plug a cord into -- you're limite to 80% of the rated circuit
capacity for the 'permanently connected' device. that's 16A load allowed,
for a 20A breaker.
*PROBABLY* not required, though some jurisdictions _are_ moving toward
requiring GFCI protection in garage/basement areas where there is a
"possibility" of water accumulating.
There is no 'downside' (other than materials cost) to doing so, however.
Requires #10 wire, _and_ 30A-rated outlets _and_ mating plugs.
Can't permanently wire 18+12A worth of devices on a single 30 A circuit,
due to the 80% restriction mentioned above.
Authoritative answer: "it depends"
On how big the space is, how much you expect to grow the number of tools,
etc. My "shop" survives on a _single_ 15A circuit. of course, it's
the 'back bedroom' of a 2BR *condo*, with about 50(!!) sq ft of 'usable'
space, and -never- more than a single tool running at a time.
One argument in favor of running a sub-panel, which you hang all the
'dangerous' tooling off of -- running lights *separately* from the main
panel -- is that you can kill, and/or "lock out" all the dangerous stuff
with a single master kill-switch at the sub-panel. A padlocked disconnect,
and you don't have to worry about kids getting into trouble when nobody's
around to supervise.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.