Shop wiring questions...

[Rodney Randal]

I have a 3 car garag...., er.. shop that is sheetrocked, and there are only 2 120v circuits in it. 1 is for the ceiling outlets used by the garag... er.. shop door openers, and 1 with 3 GFCI outlets on it.

I am wanting to add 2 120v circuits for general tool use, and 2-3 240v circuits for a new SawStop (soon to be gloat ), a cyclone DC and a larger compressor. I already have a sub panel in the shop with 7 slots available, so I think that I have the capacity.

I have some questions about the best way to go about this project:

1) If I run these circuits in EMT mounted on the sheetrock, how do they exit the panel? Do I drill a hole in the sheetrock beside the sub panel and put in a 90° elbow and then start the run along the sheetrock?

2) Where should I run the conduit - along the chair rail ( it was a model home and the garage was the sales office), or up to the ceiling and then have drops for the outlets? I am thinking that the 120v circuits will run along the chair rail (eliminate as many bends as possible), and maybe run the 220v along the ceiling (these need to run all the way around to the other side of the shop). Any pros/cons of either approach?

3) My current table saw, and the soon to be SawStop will be in the center of the shop and I don't really like cords on the floor. Does anyone have overhead runs in their shops? If you do, and it is 220v, do you just make a long(er) power cord for the tools that it serves?

4) I think that the 2 120v circuits can be run in the same conduit, but what about the 220v circuits? Do they need to be run in seperate conduits?

Any suggestions, tips, or pictures of your setups would be greatly appreciated.

Thanks,
Rodney

[Carl Crout]

just because you have 7 slots available for breakers does not mean that you have any additional capacity, may just mean that, that is the size box that they installed.
How big is the main breaker in that panel, if it has one? That is your capacity.

[Tom Hamilton]

Hi Rodney:

I have a similar set-up: three car tandem with the shop in the third bay. I also had a couple of ceiling outlets and 3 GFCI's.

I had an electrician add 2 15 amp outlets adjacent to the breaker box. From there I used 14 gauge extension cords and power strips to bring to power to the bench, miter saw and other tools. I ran the cords the length of the space (about 35 feet) up under the shelving so it is out of harms way.

The electrician also installed 2 20 amp circuits that I use for the window AC and electical water heater at the sink. I supplied the current the same way.

To drive the table saw and band saw I made an 12 gauge extension cord to bring the power from the builder installed 220 wall plug to the equipment. The cord rests in a gap in the wood floor so it is not a hazard to walking.

Enjoy your project.

Tom

[Don Baer]

Carl is correct in that you need to look at the capacity of the box and the breaker that serves it If it is a 60 amp breaker then the maximum connected loads should not exceed 100% of all load plus 50 of the largest load connected. Now that that is out of the way lets try yo anwer your question.

1) If I run these circuits in EMT mounted on the sheetrock, how do they exit the panel? Do I drill a hole in the sheetrock beside the sub panel and put in a 90° elbow and then start the run along the sheetrock?

I am assuming that this fed off of the main and it is mounted flush. If this is the case then I would get an LB fitting and used it to tape into the side of the sub panel and then connect it to a pull box surface mounted on the sheet rock. From this pull box you could feed all of your circuits.

2) Where should I run the conduit - along the chair rail ( it was a model home and the garage was the sales office), or up to the ceiling and then have drops for the outlets? I am thinking that the 120v circuits will run along the chair rail (eliminate as many bends as possible), and maybe run the 220v along the ceiling (these need to run all the way around to the other side of the shop). Any pros/cons of either approach?

That would be fine except I am not a big fan of having circuits comming out of the ceiling in the shop I like the area overhead to be free from obtructions sine swinging big pieces of lumber and sheet good around tend grab ahold of cords hanging in the air.

3) My current table saw, and the soon to be SawStop will be in the center of the shop and I don't really like cords on the floor. Does anyone have overhead runs in their shops? If you do, and it is 220v, do you just make a long(er) power cord for the tools that it serves?

See Number 2

4) I think that the 2 120v circuits can be run in the same conduit, but what about the 220v circuits? Do they need to be run in seperate conduits?

NO you don't just seperate circuit with conduit large enough for all of the circuits. I tend to oversize the conduit and even pull extra wires for future circuits.

I would run at least 2-220 circuits 1 for the DC and the other to be used for the other 220V load, unless you plan on running more then 1-220 tools at a time. Also on the 110 Volts circuits I'd run at least 2 seperate circuits. Actually if you run 2 220 circuit and 2 110V circuit that leaves you with 1 spare 110V space in your sub panel.

[Bruce Wrenn]

Before doing any wiring, I suggest you get a copy of the article in Oct 2005 Popular Woodworking on Efficent Shop Wiring. It uses a double pole breaker feeding two hots (220) and a neutral which allows for two 110 circuits out same breaker. In a small shop, you would seldom be running more than one machine at the time, other than with the DC. So circuit to TS (220) could also give you two 110 circuits. That is getting three circuits in the space of two. By adding a current sensor to one of the hots in panel box to control DC, you would also get one circuit(110) that also controls DC

[Don Baer]

Before doing any wiring, I suggest you get a copy of the article in Oct 2005 Popular Woodworking on Efficent Shop Wiring. It uses a double pole breaker feeding two hots (220) and a neutral which allows for two 110 circuits out same breaker. In a small shop, you would seldom be running more than one machine at the time, other than with the DC. So circuit to TS (220) could also give you two 110 circuits. That is getting three circuits in the space of two. By adding a current sensor to one of the hots in panel box to control DC, you would also get one circuit(110) that also controls DC

Bruce at the risk of sounding critical, I have been doing wireing of buildings and control panel for over 30 years. My dad was a contractor and I was an electrician for a long while before persuing my present profession. while I would do multiple drops on a 220 V circuit which will not be loaded at the same time I would never use one leg of a 220 V circuit to creat a 110V circuit. Think about it for a moment. Its winter time and Rod has a space heater plugged into his 110 volt recet. Now he turns on his TS and proceed to mill a piece of 4/4 Maple. Since his 1 1/2 HP saw is at close to max amps and the heater is on he exceed the FLA for the 2 pole breaker (1 leg) Oh well best case he trip the breaker Best case well I'll leave that up to you. He has plenty of capicity in his sub panel for the required circuit. electricty is not something you want to skimp on.

[Rodney Randal]

My main breaker panel has a 60A double pole breaker labeled as "Sub". My sub panel (located in the shop) currently has 17 20A breakers in it with 7 open slots available.

Carl is correct in that you need to look at the capacity of the box and the breaker that serves it If it is a 60 amp breaker then the maximum connected loads should not exceed 100% of all load plus 50 of the largest load connected. Now that that is out of the way lets try yo anwer your question.

Don, I don't think that I understand what you are saying here...

I would run at least 2-220 circuits 1 for the DC and the other to be used for the other 220V load, unless you plan on running more then 1-220 tools at a time. Also on the 110 Volts circuits I'd run at least 2 seperate circuits. Actually if you run 2 220 circuit and 2 110V circuit that leaves you with 1 spare 110V space in your sub panel.

I would like to put in 3 220 circuits - 1 for table saw, 1 for DC and 1 for compressor (all 3 could be running at the same time), and 2 110 circuits. Does it look like I have the capacity?

Thanks,
Rodney

[Fred Woodward]

What circuits are on those 20 amp breakers? What is the current draw or HP rating for the potential 220V tools? Lots of variables.

[Rodney Randal]

What circuits are on those 20 amp breakers? What is the current draw or HP rating for the potential 220V tools? Lots of variables.

The labeled circuits that are in the sub panel are:
Fridge
Dishwasher
Disposal
House GFCI
Kitchen
Garage/Living/Utility
Master bath
Kitchen plugs
Furnace
Washer
Microwave
Kitchen plugs
Furnace
Bedrooms/Hall
Master/Powder/Family
And 2 20A breakers that are not labeled...

I don't know what the current draw is on any of the 220v tools - I haven't purchased them yet. The Sawstop is rated at 3hp.

[Larry Reimer]

Rodney, sounds like you've got a bit of electrical load already in that subpanel and you're looking to add more. Probably time to do the actual load calculations and measurements.

You don't mention air conditioning load, but if that is in the subpanel also, then you definitely need to do load calculations (or have someone do them for you).

Try going to selfhelpandmore.com and their electrical section. They describe in understandable terms what you need to be doing.

[Rodney Randal]

Rodney, sounds like you've got a bit of electrical load already in that subpanel and you're looking to add more. Probably time to do the actual load calculations and measurements.

You don't mention air conditioning load, but if that is in the subpanel also, then you definitely need to do load calculations (or have someone do them for you).

Try going to selfhelpandmore.com and their electrical section. They describe in understandable terms what you need to be doing.

Larry, both AC units have breakers in the main panel. I will check out selfhelpandmore.com

Thanks,
Rodney

[Don Baer]

Rodney,
After looking at your loads on the sub panel I think you might consider adding a new Sub panel off of the main panel. What size is your main panel. It might be smarter to surface miunt a 60 or 100 amp subpanel in the garage and do your shop circuit off of it.

Wtih 7 open breaker slots you don't have enough room to do 3 220 V circuit and 2 110 Volt circuit in the garage.

[Rodney Randal]

Rodney,
After looking at your loads on the sub panel I think you might consider adding a new Sub panel off of the main panel. What size is your main panel. It might be smarter to surface miunt a 60 or 100 amp subpanel in the garage and do your shop circuit off of it.

Wtih 7 open breaker slots you don't have enough room to do 3 220 V circuit and 2 110 Volt circuit in the garage.

Don, my main is 250A, if I understand correctly. The main breaker is a double pole with each labeled as 125A. In the main there are:
A double pole 60A labeled "Sub"
A double pole 30A labeled "Dryer"
A double pole 50A labeled "AC"
A double pole 25A labeled "AC"
A single pole 20A unlabeled
A double pole 60A unlabeled

Rodney

[Rob Russell]

Carl is correct in that you need to look at the capacity of the box and the breaker that serves it If it is a 60 amp breaker then the maximum connected loads should not exceed 100% of all load plus 50 of the largest load connected. Now that that is out of the way lets try yo anwer your question.

Don,

Based on what do you quote the above "connected load" figures? There are NEC rules about continuous loads not exceeding 80% of the branch circuit overcurrent and conductor ampacity ratings (210.20 and 210.19(A)(1), respectively), but I'm curious as to where I can find something about the above reference to "connected loads".

Rodney,

In terms of running multiple circuits through the same raceway (conduit), be careful about the derating rules. What they effectively mean is that once you get more than (3) 120v or 220v circuits for a total of 6 current-carrying conductors bundled, you would have to upsize your wire. 3 circuits would be fine - the 4th circuit would force the conductor size change. These comments are based on the assumption that you'd be pulling THHN/THWN through the conduit.

Rob

[Bruce Wrenn]

Bruce at the risk of sounding critical, I have been doing wireing of buildings and control panel for over 30 years. My dad was a contractor and I was an electrician for a long while before persuing my present profession. while I would do multiple drops on a 220 V circuit which will not be loaded at the same time I would never use one leg of a 220 V circuit to creat a 110V circuit. Think about it for a moment. Its winter time and Rod has a space heater plugged into his 110 volt recet. Now he turns on his TS and proceed to mill a piece of 4/4 Maple. Since his 1 1/2 HP saw is at close to max amps and the heater is on he exceed the FLA for the 2 pole breaker (1 leg) Oh well best case he trip the breaker Best case well I'll leave that up to you. He has plenty of capicity in his sub panel for the required circuit. electricty is not something you want to skimp on.

Check out current copy of code,as this is now allowed. Do a search here and over at wood net. Because the two poles of breaker are tied together, if one trips, both trip. I'm sure that you have seen panels with the main being made up of four breakers, with tie straps on handles. What happens there if only one side is overloaded? They both trip. Any 110 circuit fed from sub panel is on one leg of a 220 circuit, isn't it?