What gauge cable do I need to power my workshop?

Reply

  #1  
Old 05-09-07, 08:56 AM
Member
Thread Starter
Join Date: Apr 2007
Posts: 14
What gauge cable do I need to power my workshop?

I am looking at running about 100 feet of cable from my breaker box to the shop behind my house. I need to be able to support about 10 kilowatts in 110 and about 10 kilowatts in 220 (maybe not so much in 110, but just rounding it out for room to grow). I saw some 6gauge wire that was rated at 55 amps, which is over 12 kilowatts in 220 (using Amps * Volts = watts ??), but just over 6 Kw in 110 (it makes sense to me that a given gauge wire could transfer a given amount of "energy" regardless of its specific properties, but I only have a "basic+" understanding of how electricity works so I may be wrong).

Will that distance cause a significant enough "power" drop to require a larger gauge than would be needed for, say, 2 feet of cable? What gauge should I be looking at for this amount of power?

Thanks!
 
Sponsored Links
  #2  
Old 05-09-07, 09:17 AM
Member
Join Date: Aug 2005
Location: USA
Posts: 995
It's easier to look at the amperage requirements for the total load that will be on the shop's subpanel.

The wire size determines the amps that can go through it, which is why you will have less power on 120V than on 240V for the same wire.

I'm assuming this shop is detached from the house?

Plus, your 120V loads will be divided between the two busses on the panel.

I think you are looking at a 100A subpanel.
 
  #3  
Old 05-09-07, 09:30 AM
Member
Join Date: Sep 2000
Location: United States
Posts: 18,497
A kilowatt is a kilowatt. Voltage doesn't matter. You need 20KW total. That's 84 amps. So you need a 100-amp panel. That normally requires #2 copper. If you run individual wires (rather than cable), you can use #3. Some inspectors may allow #4 (ask). You could save a little money by running aluminum (in heavier gauge). Bury the cable 24" deep, or wires 18" in conduit.

100 feet isn't far enough to need to increase the wire size because of that.

You'll need four wires between the structures, and grounding rod(s) at your shop.
 
  #4  
Old 05-09-07, 12:59 PM
Member
Thread Starter
Join Date: Apr 2007
Posts: 14
Thanks alot, guys!

So the best way to do this would be to just run a single "power line" (not sure what to call it) from the main fuse box out to the subpanel at the shop, and then split up the power from there? In your opinion, what would be the best way to hook that main cable up to the box?
 
  #5  
Old 05-09-07, 01:24 PM
Member
Join Date: Apr 2007
Location: USA
Posts: 340
If by single you mean "one" then you can't do it and have two phase wiring so you will require two conductors.
 
  #6  
Old 05-09-07, 01:36 PM
Member
Join Date: Aug 2005
Location: USA
Posts: 995
A subpanel is required for multiple circuits in a detached building. So, yes, only one feed to the shop is required, the one that powers the subpanel. This feed will require 4 wires, and you will also need a 5/8" driven ground rod at the shop panel.
 
  #7  
Old 05-09-07, 01:40 PM
Member
Join Date: Apr 2007
Location: USA
Posts: 340
Do you run the neutral and ground from the main panel on a sub panel?
 
  #8  
Old 05-09-07, 01:44 PM
Member
Join Date: Aug 2005
Location: USA
Posts: 995
Whether the sub comes from a main or another sub, you run all four wires.

Legally, there are many times when you only need 3 wires out to a detached building, but I rarely recommend it.
 
  #9  
Old 05-09-07, 01:50 PM
Member
Thread Starter
Join Date: Apr 2007
Posts: 14
*edit*

Alot of info was posted while I was replying, heh.

So I need to run 4 3-gauge wires out to the shop? Two for "Hot," one for "Ground," and one for "Neutral?"
 
  #10  
Old 05-09-07, 07:30 PM
Member
Join Date: Sep 2000
Location: United States
Posts: 18,497
I hope you appreciate the complexity of the project you are undertaking. There are a few hundred other details you need to learn before beginning. I'm not sure we can cover them all in this thread.

The grounding wire run between structures only needs to be #8 (copper).

There isn't a "best way" to connect to the main panel. There is only one way. You will connect the wires in the main panel to a 100-amp breaker. The four wires between buildings is called a feeder.
 
  #11  
Old 05-10-07, 05:19 PM
Member
Thread Starter
Join Date: Apr 2007
Posts: 14
Ok, so I need 4 individual wires to run from the main panel to the subpanel in the shop, right? Two hot, one neutral, and one grund? I havent been able to find any single cables that contain hot wires larger than 6gauge. If I were to run each wires individually, what gauge should each of the wires be? A 3gauge wire for each "hot" line, and then what gauge for the neutral and ground wires?

At lowes they have 125A panels that say they are specifically designed for workshops, home additions, basements, etc. It says it can house 6 1" fuses (240V?), or 12 .5" fuses (120V?), which Im sure will be plenty. Does that sound like what I need?

And for what it's worth, my best friend's dad is an electrician and is helping us with parts of this as a favor, but he is a busy man and I don't want to bother him with all sorts of repetitive questions (Im sure you all know how annoying it can be to offer a favor and it end up being an annoying chore for you), so I am trying to find out as much as I can on my own so it will be quick for him to check and connect everything.
 
  #12  
Old 05-10-07, 05:48 PM
Member
Join Date: Aug 2005
Location: USA
Posts: 995
You didn't tell us the make and type of the panel, but the size of the breakers (don't call them fuses) doesn't matter, just how they are tied together. The thinner breakers are more expensive, but give you lots more room.
 
  #13  
Old 05-11-07, 07:04 AM
Forum Topic Moderator
Join Date: Sep 2005
Location: USA
Posts: 4,115
The panel is something you never want to skimp in terms of size. Just because you need 6 circuits today, I can guarantee within 10 years you'll want more.

I would personally get a 12-slot panel for a workshop. 6 just seems a bit limiting. Plus, for the extra $20 or so, it'll be worth it.

Also, though the panel you mentioned is suitable for 6 full size breakers or 12 half-size breakers, most people here I think would recommend staying away from the half-size breakers if possible. The larger ones dissipate heat better, probably more reliable, and likely last longer. So if it were me, I'd choose a 12-slot panel, or a 12/24 (12 full, 24 half), though I would plan on using only 12.

You can find cable assemblies that have larger wire, just probably not at HD/Lowes. Try an electrical supply house. Cable assemblies will certainly be easier to install than conduit and individual conductors.

Good luck!

-Mike
 
  #14  
Old 05-11-07, 08:31 AM
Member
Thread Starter
Join Date: Apr 2007
Posts: 14
Thanks! You might be right, though. Here is what I was planning:

Using all 1", I could use 3 for 220V (one for the CNC Mill, one for the welder, and another later for a plasma cutter or something if I decide to add that). I could then use 2 spaces for 110v Dual socket outlets (Drill Press, Bandsaw, maybe the AC unit, and then the last one could go to a power strip for the smaller things like bench grinder, small bandsaw, radio, etc), and the last one could go to the lights. Dang... I think you ARE right, heh... that's really limiting.

Could I use the 1/2" fuses for any of these? What about if I mounted a small fan behind / over / under the fusebox to aid in cooling? Could I then use more 1/2" fuses? Aren't the thicker fuses required for 220V? I forget how it worked since we wired in a 220V in the garage.

But yeah Im just curious what size each of the four feeder wires would have to be?
 
  #15  
Old 05-11-07, 08:35 AM
Member
Join Date: Aug 2005
Location: USA
Posts: 995
I've never seen or heard of a failure in a 1/2-size breaker. I use them very often. They are designed and UL-listed to do what they do as well as full-size breakers. That is only the second time in my life I've even seen them questioned.

240V (not 220V) is also possible with the 1/2-size breakers (not fuses). This will usually be a 2" breaker with a 240V circuit and two 120V circuits built into one to make sure it connects to the busses properly.

Now, if you're going to run a receptacle to each of those 240V machines, the spaces will still fill up quickly; look for the bigger panel.

But things like welders and plasma cutters can often use the same receptacle and circuit, if you don't mind swapping them out. Which machines do you have?
 
  #16  
Old 05-11-07, 11:21 AM
Member
Thread Starter
Join Date: Apr 2007
Posts: 14
I have a Chicago Electric 220V (240?) Mig welder. The CNC machine Im going to buy once the shop is finished is a CNC Master's mill, that will likely use about 2-3 Kw on 240 Single Phase VAC (a 2 HP spindle motor, plus the stepper motors, and the computer Ill use to control it). I dont have a plasma cutter at the moment and I am still contemplating getting one (not sure if Id use it enough to justify the >$1k price tag, but it's a definite possiblity). Oh and also the air compressor, 23.5 amps (start up), and 12.5 amps (no load). Plus all the smaller 110v tools (bench grinder, drill press, large bandsaw, small bandsaw), and accessories (fan, radio, small AC unit, battery charger, etc).

*edit* Forgot link:

http://www.lowes.com/lowes/lkn?action=productList&N=0&Ntk=i_products&Ntt=main%20lug

*/edit*

Just so we're on the same page, out of these, which one would be best for my application? When they say like "12/24" or "4/8" does that designate how many breakers it can hold in 1" and 1/2" styles, or am I confused again?

Thanks for all the advice!
 
  #17  
Old 05-11-07, 11:35 AM
Forum Topic Moderator
Join Date: Sep 2005
Location: USA
Posts: 4,115
Mac - I'm by no means an expert, so my knowlege of full versus half-size breakers is based on others' input. I'll defer to more knowledgeable members here.

Yes, the panels are specified as 12/24 meaning 12 full size breakers of 24 half-size breakers. You'll see some panels that might say 12/18 which implies that only some of the positions accept half-size breakers.
 
  #18  
Old 05-11-07, 01:28 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,388
The bigger (more spaces) panel is just a fraction of what it will cost if in the future you need more circuit breakers than a smaller panel will hold.
 
  #19  
Old 05-11-07, 03:56 PM
Member
Join Date: Aug 2005
Location: USA
Posts: 995
Yep. And a 12/24 will give you a lot of flexibility for adding dedicated circuits to specific machines. And I'd still be filling it with the 1/2-size breakers that are available, and then using full-size breakers for the less common ones.

Are you the same JMcDonald at www.weldingweb.com?
 
  #20  
Old 05-11-07, 09:48 PM
Member
Thread Starter
Join Date: Apr 2007
Posts: 14
Yes I am the same guy, heh.

Today I talked to the electrical specialist and another guy who apparently builds homes and was looking for electrical supplies for his own house. They were extremely helpful and pointed me to everything I needed (including the wiring... you guys were right about the aluminum vs copper). 2 / 2 / 2 / 4 Aluminum cable, a 125A 12/24 box, and gave me alot of advise on breaker selection and wiring and grounding rods, etc. They also both agreed that 1/2" breakers were just fine and advised them just to save space.
 
  #21  
Old 05-12-07, 11:04 PM
Member
Thread Starter
Join Date: Apr 2007
Posts: 14
Thanks for all the advice! I spoke with the electrical guy at Lowes and also a home builder that happened to be there looking for parts for his house. I explained my goals and the limited amounts of knowledge about the subject, and they filled me in the rest of the way. I ended up with a 125A, 12/24 panel, and about 7 tons of 2/2/2/4 Aluminum cable, both of which fit into all of your recommendations as well. The home builder even explained how and what type of breakers to use for each application, along with how to do the ground rod and basic wiring for the shop.

Again, thanks!
 
  #22  
Old 05-20-07, 08:06 PM
Member
Thread Starter
Join Date: Apr 2007
Posts: 14
Real quick:

To connect the feeder cable for the shop to my main panel for the house, do I just use a 100A breaker in the main panel, with the feeder (2-2-2-4 Aluminum cable) coming out of that?
 
  #23  
Old 05-20-07, 09:54 PM
Member
Join Date: Aug 2005
Location: USA
Posts: 995
Yeah, the two hots on the 100A breaker, and the ground and neutral on their buss[es], which might be one and the same in the main.
 
  #24  
Old 06-08-07, 01:14 AM
Member
Thread Starter
Join Date: Apr 2007
Posts: 14
To clarify, do I really only need one breaker that goes to the main panel? From how I was told to set up the 220v welder, it seems you'd have to tap in to both poles at the main panel to get 240 at the subpanel in the shop? Or am I missing something here (either in how the breaker connects in the main panel, or how the subpanel splits power between 120 and 240)?
 
  #25  
Old 06-08-07, 03:46 AM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
You need one breaker at the main panel, but it needs to be a 240 volt breaker. The breaker will be twice the width of a 120 volt breaker.
 
  #26  
Old 06-08-07, 10:45 AM
Member
Join Date: Aug 2005
Location: USA
Posts: 995
2-pole breaker gives you two sides of the 240V, and the grounded neutral buss gives you the middle (120V).
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'