Running electricity to my toolshed

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  #1  
Old 08-03-05, 10:56 PM
colpaarm
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Running electricity to my toolshed

Just finished building a tool shed from scratch and have started the process of running electricity to it. I'm in the process of running a 30 amp circuit to it. Already trenched and added #10 underground wire (in conduit) from the shed to the house. I'm going to install a subpanel in there. I know I didn't need the conduit, but I'm an overkill kind of guy. I wasn't going to add the conduit because I heard some electricians talk about heat build up in the conduit, but could never get two electricians to agree.

Anway, my question is why do I need a double pole breaker? I know that the breaker should be GFCI for obvious reasons. However, if I wanted to use a single pole breaker to feed my subpanel, could I? I'm thinking that the only bad thing about using a single pole breaker at the house is that I could never run 220-240 volt stuff in the tool shed. The home depot book just says, "Do it", which is great. It's the same book that taught me how to build the shed. However, I was able to search the web and get supplemental knowledge, so that I knew why the heck I was doing what I was doing. Not so with the subpanel. Haven't seen this topic covered too well via the internet. Anyone care to shed some light on this subject for me? Thanks in advance.
 
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  #2  
Old 08-04-05, 01:23 AM
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" my question is why do I need a double pole breaker "
Only if you want 240 volts.


Start with this link first.
http://forum.doityourself.com/showthread.php?t=225048
 
  #3  
Old 08-04-05, 05:18 AM
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How far is the shed from the main panel? The longer the run, the greater the voltage drop. A 240 volt run will decrease the voltage drop if the loads on each leg of the 240 are fairly even.

Another reason for 240 volts is more power. If you use a single pole (120 volt) 30 amp breaker to feed your sub panel then you will have at most 30 amps at the shed. However, if you use a double pole (240 volt) breaker, then you can have 60 amps at the shed.

Don't skimp.
 
  #4  
Old 08-04-05, 06:13 AM
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Make sure the wire in the conduit is rated for wet locations. Are you planning on just having one circuit at your shed? If you want both 240 Volts and 120 Volts out there, it might be better to install a subpanel and run circuts from there. I believe there are outlets made that have both a 120 V plug and a 240 V plug if you are just running one circuit out to the shed.
 
  #5  
Old 08-04-05, 09:28 AM
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I wasn't going to add the conduit because I heard some electricians talk about heat build up in the conduit, but could never get two electricians to agree
.
This is a no brainer, conduit installations are far superior to direct burial. There is no concern for heat build if done properly. If you have electricians disagreeing on this I wouldnt hire them. Example: If you pull cable like UF-B 10/3G thru conduit you have a heat build up problem and a code violation. If you pull individual wires THHN/THWN then you are fine, plus you can use a higher ampacity column on the tables in many cases.
Anway, my question is why do I need a double pole breaker?
I am in total agreement with racraft on this. You would be short changing your self not to ad the one extra wire and double your power. Plus sub-panels are meant to be served by a 240 volt circuit by design. Using a double pole breaker is not so much you have the ability to operate things that are 240 volt but to double the available power for 120 volts.
I know that the breaker should be GFCI for obvious reasons.
It does not have to be gfci. Any readily accessible receptacles on the branch circuits in the shed need to be gfci.
However, if I wanted to use a single pole breaker to feed my subpanel, could I?
Well I suppose you could but I see a serious issue down the road if someone would want to put a double pole breaker in a panel fed by 120 volts only. The ones I have come across that are fed with 120 volts usually have been jumpered to both main bus lugs in the subpanel. An unknowing person if they dont notice this could have some serious problems when adding a double pole breaker.

If you install a 30 amp single pole you must install the subpanel and "fuse the circuit down" using 15 and 20 amp breakers in order to feed general purpose duplex receptacles in the shed.
 

Last edited by Roger; 08-04-05 at 09:44 AM.
  #6  
Old 08-06-05, 05:48 AM
colpaarm
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Okay, I was out of town so sorry for not responding sooner.

Roger, I wish I handled this area like I did every other. Understand EVERYTHING before proceeding. I did have some electricians tell me to use individual wires if I was going to use conduit, but suprisingly the home depot book doesn't mention this. So right now, I have UF-B cable (now they didn't recommend that, but they did recommend regular house wiring) in plastic conduit buried 18" deep. For the amount of work that it took me to get it there in the first place, I'd be inclinded to just leave it there. I oversized the conduit at an inch and figure the heat build up shouldn't be an issue. However, I like doing things the right way and don't like having my name attached to something with the words "code violation" next to it! The day I sell my house, I want an inspector to look at my work and give two thumbs up.

I definitely have no problems using a double pole breaker. I just wasn't 100% clear on why. I'll look at the link that GWIZ provided to gain more knowledge. However, in the mean time, I'll ask a question that is the result of what racraft mentioned. You said that if I use a double pole breaker, I can get 60 amps inside the shed. Would that be from using a double pole breaker at the subpanel? Wouldn't that just increase the voltage? Could you explain that a little? Thanks in advance.

Along with me redigging the trench (which will be a heck of a lot easier this time around but still a heck of a lot of work), I'd lose about $70 worth of UF-B wiring (unless I can salvage my loss with eBay). Plus, I'd have to pay for the new separate wiring. In short, do you think it's that big a mistake that I should redo it properly? If I do it with individual wires, do I bring them on both sides to junction boxes, then use regular inside wire (I believe that's NF-B) to go from the junction boxes to the panels?

Just to answer some previous posters questions, I plan on adding a subpanel in the shed. So the cable running from my house to the shed would be the feeder cable to the subpanel. Initially, I was going to have three circuits comng out of the subpanel. One 15A for the lights + smoke detector, one 20A circuit for the outlets and one dedicated 20A circuit for a plug hanging on the outside of the shed. I believe that the subpanel I was going to but could handle six circuits. Guys, thanks for the help.
 
  #7  
Old 08-06-05, 06:04 AM
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You can leave the wire in the conduit. How many wires is in this cable?
 
  #8  
Old 08-06-05, 06:54 AM
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If your wire is UF 10-3 with ground, then I would leave it. If its 10-2 with ground then I would replace it. If it's NM type wire then you MUST replace it, as it will rot when it gets wet. Under no circumstances can you use NM type wire underground, even in conduit. Underground conduit gets wet (at least from condensation) and therefor the wires gets wet.

If you have to pull the wire and replace it, consider a lesson learned. I have no idea what book you are referring to at Home Depot, but it is incorrect and obviously not worth paying attention to.

You should not have to dig anything up. You should be able to pull the existing cable out, using it as a pull string for the new wires. And I do recommend individual wires (THWN). Use pulling lubricant (not soap, petroleum jelly or anything else) and you should be okay.

If you use a double pole breaker and run 240 volts to the shed you have 240 volts at 30 amps. Each side of the 240 volts is at 30 amps. Since each side is 120 volts, you have two runs of 120 volts at 30 amps. This would mean you could install four circuits in your shed, and safely pull 15 amps through each circuit.
 
  #9  
Old 08-06-05, 07:42 AM
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When I do a feed for a garage or shed with number 10 I use 4 circuits too, usually 2 15's and 2 20's, put lights and misc stuff on the 15's and recepts on the 20's.
 
  #10  
Old 08-06-05, 10:21 AM
colpaarm
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Okay, you guys just made me feel a LOT better! I'm using 10/3 UF-B cable. The only concern I have at this point is heat build up. With one inch conduit, I don't know how much of a concern this is. I was already planning a Saturday dedicated to redigging a trench I just finished filling a week ago.

I'm going to re-read the home depot book before indicting it. They definiitely were not all that informative in this one section, but I don't believe it mentioned putting UF-B in conduit. I was the genius there.

So I think I understand this. 240 V at 30A or 120V at 60A. Is that about right? And should I run the wires into boxes or should I just run them straight to the panel (or subpanel in the case of my tool shed)? My thinking was, if I ever decided in the end to run individual wires, I would just have to deal with the wire running in the ground, and wouldn't have to worry about messing with sheetrock again. Once again, thanks, guys.
 
  #11  
Old 08-07-05, 02:49 AM
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" So I think I understand this. 240 V at 30A or 120V at 60A. Is that about right? "
No.

Its a long explanation.
In short,

The breakers are 30 amp that's the most you will pull 30 amps.
You can pull more power with the higher voltage.
240 volts x 30 amps = 7200 watts
120 volts x 30 amps = 3600 watts
120 volts x 60 amps = 7200 watts
Running a 7200 watt 240 volt heater will pull 30 amps.
The Equivalent, a 120 volt 7200 watt heater will pull 60 amps.
The 240v 30 amp heater uses the equivalent wattage power as 120v at 60 amps heater.
The 120 volt 7200 watt heater will require larger wire and larger breaker.

If you plug in a 15 amp toaster on Line1 L1 and a second 15 amp toaster on the other line L2
the two toasters will be sharing 240 volts but only pulling a total of 15 amps.
240v x 15 amps = 3600 watts.

If you plug both toasters on L1 120 volts the combined current pull will be 30 amps
120v x 30 amps = 3600 watts.

Maybe-maybe this link will help.
http://forum.doityourself.com/showthread.php?t=216570
 
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