Replies

1. 
   NickC | Oct 28, 2002 08:51am | #1

   Sounds like you might have a 1 HP and a 3 HP motor going at the same time. That will draw more than 15 A at 230 V. Nick

2. 
   PlaneWood | Oct 28, 2002 04:28pm | #2

   Don -

   Is the sub panel connected to the breaker box that supplies the house?  If so, you should try to figure out how many amps, total, this will cause to be drawn through the main breaker (located at the top of the breaker box). 

   In my case, the house main breaker was getting excessively hot due to being underrated for the current going through it.  The house has 2 central AC's, electric dryer, plus all the other stuff.   That alone was drawing over 60 amps when everything was running.  Adding 30+ amps from the shop was pushing the main breaker box to it's limit (100 amp service).

   I installed a different 100 amp breaker box in the shop and ran it directly from the meter, bypassing the house breaker box.

   For the question you asked, you should have two 30 amp breakers.

   PlaneWood by Mike_in_Katy
   PlaneWood

1. 
   fonsecad | Oct 28, 2002 05:07pm | #3

   I have a 200 amp "pass-thru" panel which has 4 extra unused slots (this is where I planned on putting a 125 breaker).  I have a seperate 200 amp interior sub-panel for my house with three, or so unused slots.

   I planned on running from the meter-box (pass-thru panel) to the new 125 amp shop sub-panel.  My FAU is gas, but I still have inside the house double ovens, dryer, A/C, cooktop, and mico.  Should I use a 100 or 125 amp panel?  I found a 125 panel for $30 that comes with 5 breakers this seems like a good deal.  Will a 125 shop panel and any effect on the house panel?

   Thanks,

   Don

1. 
   DouglasABaker | Oct 28, 2002 11:18pm | #4

   It sounds like your situation is fairly similar to mine when I did my shop.

   I also did not have enough breaker slots available in my main panel, plus I wanted the ability to shut my shop tools off with a single switch AND not have to worry about the lights going out if I tripped the "main" breaker.

   So, I wired up a subpanel.  As it happens, I used a 100A _rated_ subpanel, but I only used a 60A breaker in the main panel.  I run my main lights out of the main panel, but my aux lights are out of the subpanel.

   60A has proven to be more than adequate for running, at any given time, a 1.5hp (~12A @ 120V) dust collector, a 12" planer (~10-12A @ 120V), a 6" jointer (~5-6A @ 120V), an air cleaner (~2-3A @ 120V) and 2 sets of aux lights (~3-4A @ 120V).  Note that these are all steady state amperages, meaning not under load, and not @ startup.  I can also substitute, at will, a Unisaw (~5-6A @ 240V) for either of the other 2 tools.

   The point is, you will be very hard pressed, as a 1 man shop, to use more than about 40A at any given time - you physically cannot run that many machines!

   And don't get confused by the fact that some machines draw considerably higher amperage at startup - while that is the case, circuit breakers have a delay built into them to prevent them from tripping during this period.  Unisaws, for example, draw well in excess of the 20A that the circuit I have it on is rated for - but it only draws that load for an infinitessimally short period of time, and the breaker doesn't trip.

   Remember - the size breaker you have feeding your subpanel can be smaller than the rating of the subpanel - it simply can't be any larger.

   And no, unless you plan on running both ovens, the cooktop, the micro, the A/C, dryer, your fridge, and all the tools in your shop at the same time, it should not affect your overall house panel.

   Doug

3. 
   watkinsjd | Oct 28, 2002 11:58pm | #5

   Don,

   I highly recommend that you consult a qualified electrician, at least for design help.  I sold panels and breakers for GE in a past life so I have a decent background and can run the wire, etc., but electricity can be dangerous stuff.  The issues are more complex than you might think. Fortunately my next door neighbor is a journeyman electrician and I do his taxes, quid pro quo.

   Last week there was a fire in our town that took the life of a 9 year old so safety is even more at the front of my mind right now.

   John

4. 
   Elcoholic | Oct 29, 2002 12:10am | #6

   Don,

   Here's the basics.  The code requires any hard-wired motor load over 1/3 hp to be on a dedicated circuit.  Plug and cord connected equipment gives you more leeway.  Let's say you have 2 hp and a 3 hp loads on the same 240V receptacle circuit.

   1hp = 8 amps FLC

   3hp = 17 amps FLC

   25% of the larger = 4.25 amps

   total load for wire sizing = 29.25

   Cu Wire Size (75 deg. C rating) = #10 (max for this size is 35 A)

   Max Breaker Size = 30A

   The breaker has to protect the wire and the wiring devices, which in this case are the receptacles.  So you'll have to use 30 A rated receptacles for this example.  Where you may run into trouble is the running overload protection for the smaller motor (when it's the only one running) if it doesn't have a starter or integral overloads.  The 30 A breaker may be too big for the 1 hp motor to see it.   The other problem may be tripping the breaker starting the second machine or loading them both.  If this happens you may be temped to go to a bigger breaker, but your recepts and wiring will be underprotected.  For a single motor that trips on starting a special motor circuit protector can be used, but I'm not aware of any MCP's for multi-motor circuits.

   The best bet would be to make room for dedicated circuits in your sub-panel.  I have (3) dedicated 30A twistlock recept circuits in my shop (garage) in which I can plug any of my 220V machines.  Here are few rules and ideas to maximize your panel space elsewhere.

   • Don't exceed 80% of the breaker rating per code.
   • Code requires a dedicated circuit for the washing machine outlet.
   • Never mix stationary lighting and receptacles on the same circuit.  (Do you really want to be holding that 3 hp router in the dark while it spins down?)
   • Use double side by side 1P breakers. That way you can get (2) 20A circuits in the panel space of 1.
   • Use 20A circuits, receptacles and #12 wire.  Figure 180 watts per duplex receptacle.  That means you can put 10 on a 20A circuit per code.  Unless you have old fluorscents fixtures (w/ starters) figure 32 watts per 4' tube.  You can get 30 (2) tube fixtures on (1) 20A circuit.  If you want diversity switching on your lighting use switches not breakers.
   • The other advantage of #12 wiring is low voltage drop which will help your portable tools run better on extension cords.

   So how big's your garage anyway?  Hope this helps.

   John O'Connell - JKO Handcrafted Woodworking

   Life is tough.  It's tougher if you're stupid - John Wayne

5. 
   MajorWool | Oct 29, 2002 03:16am | #7

   First thing I'd do is look at the plugs on the machines. If your 3HP tablesaw came with a 20A plug, then I'd put in a 20 A circuit for it. Two things to keep in mind: that a 30A circuit requires 30A plugs on all machines and 30A receptacles, and do you really want a length of 14/3 hanging off that 30A receptacle. I'd rather have a breaker trip closer to the safety limit of my power cord. A 30A 240 circuit is 7,200 watts of available power before the breaker trips, which means your damaged 14/3 sawcord could be a fire hazard with only 20A going through it, and the breaker wouldn't be close to tripping. I had a 12/24 subpanel put in so that even when using the full size breakers, I still had capacity for (2) 20A lights, (2) 20A 120V receptacles, (2) 220V 20A and (2) 220V 30A circuits. The cost difference between it and a 6/12 box was $5, so unless you are tight for room, get a subpanel 100% bigger than what you think you need. I plan to convert all the 120 motors to 220 so that power draw is more symmetrical, ie, I can't be drawing 60A of 120 on one phase while the other is empty. Also, make sure you set the box up so that your circuits are staggered, lights on both phases, outlets on both phases, etc. My subpanel is all fed off a 60A in the main, but I doubt I'll ever reach capacity even with friends over.

1. 
   fonsecad | Oct 29, 2002 03:47am | #8

   Wow, thanks for all the feedback!

   My garage BTW is a two car double deep, or 980 sq. ft.  This is a temporary situation until I can add on this winter.  I am thinking on making the dedicated shop 600 sq. ft., with enough room to drive my truck through to the back yard.  My wife has issues with no cars, truck, or trailer parked in the driveway, and that her spot never be blocked, otherwise I’m free to do as I please.

   Do they make a 100-amp panel that has more than 12 slots?  The only panel I saw at Depot was either a 100, or 125 with 12 slots.  The panel I picked-up was a square D that comes with 5-20 amp breakers already installed.  I will return it and re-think things. 

   The slim-line breakers are a good idea, that's what I have for the house sub-panel.  I was hoping to keep the entire shop electrical breakered inside the shop if possible.  I like the idea of all dedicated circuits too; I just need a bigger panel.  Will the building department allow you to use a smaller rated main breaker to feed a sub-panel than what the panel is rated for?

   I planned on using 12-gauge for 120/20 amp circuits, even for lighting, and 10-gauge wire for all 220/30 amps.  I like the idea of using all 12-gauage wires for all, even 220, and having dedicated runs if space is available.

    

   Don

1. 
   MajorWool | Oct 29, 2002 04:24am | #9

   The Siemens 12/24 is about $25 at HD. You will have to buy a separate ground buss and screw it to the panel. The ground and neutral in the sub have to be isolated from eachother. Keep in mind that the doubled (1/2 space) breakers are twice as expensive per branch. The nice thing about using the 2-pole full size breakers is that it is much harder to wire them incorrectly when using 12/3 etc.

   The breaker for the branch circuit used to supply the sub-panel in your main panel will determine the wire size to the sub-panel. When they say a panel is 125A, they mean that each buss bar in the panel is rated at 125A; you can put less of a load on it, but not more. In the case of a subpanel with a main-breaker, that 100-125A breaker at the top will function more as an on-off switch if the breaker supplying it in the main panel is rated for less current, say 40-100A, since the main panel breaker will trip first, theoretically. Keep in mind that since you don't use everything at once, you can have a total circuit draw in a sub-panel that is much higher than the actual supply to that sub-panel. In my example, I have 140A of breakers on a 60A supply, but rarely draw above 40A. If too many things get turned on, I have to make a trip to the basement. ;-)

1. 
   fonsecad | Oct 29, 2002 06:19am | #10

   Thanks Wood,

   I'll have to check out HD again and look for the larger panel.  I have the room since I haven't built the shop yet, but I would like to keep the costs down.  Does it make sense to pay for the larger wire to feed the sub-panel just in case, or will a 60 amp breaker more than meet my needs?

   Don

1. 
   MajorWool | Oct 29, 2002 09:40am | #11

   I think everything has to be looked at on a case by case situation. You didn't mention if your garage was attached or detached, whether you could run from the main panel to the subpanel via conduit or with 6/3 or 4/3 Romex, or how far you needed to go. One thing that helped me decide was a bunch of free 1" metal conduit from a renovation at work. If they had ripped out 1 1/4", I might have splurged for #4, but went with #6 as it really met my realistic needs. FWIW, pulling 3 #12 through 1/2" EMT is trivial compared to pulling 3 #6 and a #10 ground through 70 ft of conduit.

   Even though things are on bigger circuits, they usually don't take the rated power. A 3HP cabinet saw usually draws in the 13-16A range so it would likely run fine on a 20A. Probably all other 3HP machines would be the same. I think a 5HP single phase is around 25A. My Jet DC650 is rated at 11/5.5 for 120 or 220. Keep in mind that changing tools to 220 requires new cords and plugs. If my Jet were modified to 220, I wouldn't be able to use it as the shop vac from heck* at the moment in the house. The 30A are more for welders and such.

   Most of it comes down to planning so that your loads on each leg are balanced. 80A on one leg will cause the breaker to trip, but 40 on each leg will be fine. The 220's are nice and symetrical this way.

   * I'm currently removing a bunch of extremely old and dirty loose rock wool insulation from my attic. This stuff is nasty and full of junk from many reroofs and what not. I hooked the 650 up to one of those cyclone trash can covers with a 10' piece of 4", and out the other side with another 10' piece of 4" that reduces down to 2.5" so I can use my 14 ft of shop-vac hose and wands. It has been a dream to use, it sucks just enough to move the stuff through the tube but not enough to pull everything through the can. I also swapped the lower DC bag for a 42 gal contractor bag and so far so good. I pulled out 3-400 lbs of insulation with it last weekend, and it was great getting the stuff way out in the eaves while still having headroom where I was. The best part is being able to cover the 30 gal trash can with its lid, carry it through the house w/o a mess, and then transfer into contractor bags outside. I can't wait to see if it works on the leaves as well. ;-)

6. 
   watkinsjd | Oct 30, 2002 06:31pm | #12

   Don,

   If you havn't already read enough about wiring your shop there is a very comprehensive article at http://WWW.theoak.com on electricity in the woodshop.

   By the way, a recent change in the code effective in this area calls for the cable to have two conductors (for 220V), a neutral and a ground be run from the main panel to a sub-panel and that the neutral to ground strap on the sub-panel be removed.  I am doing the same thing you are to my garage right now.

   Basic rule, size the wire to the load and the breaker to the wire.  Not the other way around.

   Be careful, it's really easy to know enough to THINK you know enough with this stuff.

   John

1. 
   fonsecad | Oct 31, 2002 07:56am | #13

   Thanks for the info, and the link.  Your last statement really hit home.  I've been a remodeling contractor for years and have always done my own wiring, and have never run into problems.  Inspectors have complemented me on work, and I never have thought twice about things.  Gathering info on wiring my shop, with all the 220's, has really opened my eyes to how little I really know.  When you do the same sorts of jobs all day long (kitchen and baths) you run into the same old challenges, and you learn what the inspector are looking for.  This is a whole new animal.  Thanks again.

   I went shopping for a panel again today while picking up supplies for other jobs.  The largest panel for either 100 or 125 amps is a 12/24 slotted, unless you go to a 200-amp panel, then it's 20/40.  Should I go to a electrical wholesale house?  What size panel are you going to use?

   Don

1. 
   MajorWool | Oct 31, 2002 10:28am | #14

   I was poking in Mullins Residential wiring book tonight, and in the chapter on motors (NEC section 422), two things caught my eye. One, the branch has to support 125% of the full time load, and two, the breaker can't be more than 250% of the load. This doesn't appear to be only for hard wired motors, and I think it serves as a suggestion that one shouldn't put in 30A circuits for 10A motors.

2. 
   smijal | Oct 31, 2002 02:30pm | #15

   Don,

   When you are out looking at Main panels to use, be sure to check and see if that particular panel can house half size breakers. This is especially true for the Square D  panels. I just finished wiring my shop (attached to the garage like yours) and needed just one more sircuit. I bought a slim line double breaker (2 separate breakers in a single sized case) and found that my panel will not accomidate those breakers. A call to the Techs at Square D confirmed what I thought.  Just a heads up.

   Stan

3. 
   watkinsjd | Oct 31, 2002 04:40pm | #16

   Check out http://ecatalog.squared.com/catalog/html/sections/01/17201013.htm#1009154

   This is a catalog listing of the Square D Homeline load centers.  I am still struggling with the planning part but I will likely get the 16 slot box.  That would allow 6 220V and 8 (4 tandems) 110V breakers which should cover my needs quite well.

   We have very cheap electric so I need extra slots to supply the heating devices.  Also, I am a firm beliver in overkill no matter what kind of project I am doing.  You will always find a use for extra slots and it is cheaper to put them in now than later.

   Don't let the list prices scare you.  These products are heavily discounted.

   John

1. 
   fonsecad | Nov 01, 2002 07:16am | #17

   More good info thanks everyone.  I've decided on dedicated circuits on all major machines, three for power tools, and one for lights.  That puts me at a min. of 17 slots even with slim-breakers, so I will buy the 200-amp sub-panel with 20/40 slots.  This will give me extra room for the future, and allow me to run 12-gauge wire with no larger than 20 amp breakers.  My shop will be, I think around 600 sq. ft., so the runs won't be too long.

   I just put together my new Jet 10 cabinet saw with their cantilever-sliding table.  Wow!  I forgot how much room these things takes up, but it sure seems nice.  I will finish dialing it in tomorrow and look for some temporary power from the house panel to give it a test run.  I’ll have to use my existing garage to layout all the machines and see if the 24 ft. by 25 ft. will be enough.

   Don