Wiring a shed.
I have 3 lines of 12-2 UF in conduit 35 feet from my house to my shed. Three of the wires 6 wires run between three-ways switches at the shed and house controling the outside lights at the shed. The other three come from 2 breakers at the main panel with a common ground and are used to power the shed’s inside light circuit and outlets.
I want to bring this up to code:
1. Do I need a load/center in the shed?
2. Do I need to replace the 3 lines of 12-2 with a single bigger wire (like 10-3)? If so, can I keep the 12-2 there to come back to the three way switch?
3. Do I need a ground rod at the shed?
Thanks
Replies
Not an electrican, but is the power on a GFIC ( breaker or outlet).
How big is the shed, and how many electrical boxs, lights?
The outlets are gfic protected. The shed is 10x10. Two overhead inside lights. Three 2-gang outlets. Two outside lights.
You are ok the way you are. You just have two branch circuits that happen to run outside the house. Nothing illegal about it.
Now if you are wanting to add a larger service for future equipment use, you may need to add a subpanel and all that it involves. Switching to a #10 ga. wire only gets you 10 more amps on each leg. You already have 20 amp on each breaker serving the shed now (40 amp total), so you are only gaining a 50% increases in service at the shed.
What are your plans for the shed?
Dave
Yeah, if you were wanting to upgrade you'd probably want to pull a 240V service, and you'd generally need to install a "grounding electrode system" for the shed.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
So the grounding electrode requirement is only if I need 240V?
The grounding electrode system (ground rods) would likely be needed (or at least advised) if you put in a subpanel.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Actually he has 240, whether he uses it or not.The limitation is that he is limited to ONE circuit. And a multiwire circuit is ONE circuit.
I thought I had two circuits since at the main box the wires connect to two 20-amp breakers. I could connect them to a 2-pole breaker if that would turn it into "one" circuit and thereby avoid having to do more in the shed. But that doesn't sound correct to me. What am I missing?
A multi-wire circuit is treated as being a single circuit.A multi-wire circuit consists of the two hots (on different legs) and a shared neutral that only carries the difference.A 2 pole breaker is not required on a multi-wire circuit unless a single device has both hot legs on it. That could be a 240 receptacle, or it could be a duplex receptacle that is split with one 1/2 on one leg and the other 1/2 on the 2nd leg.However, some people like to always put them on 2 pole breakers to eliminate confusion in the future and also to make sure that the whole circuit is dead whne working on one part of it.
Great. I just put them both on a two pole breaker. Thanks for your help.
I don't expect to need more power, so if I am legal the way it is, I'm happy.
1. Do I need a load/center in the shed?
You need a Disconnecting Means at the shed. This is a switch, or group of switches, that when thrown, disconnects all ungrounded conductors. It must be possible to disconnect all power with no more than 6 hand motions. In this case, it can be as simple as two 2-pole switches in a 2-gang box.
Refer to NEC 225-31 and 225-32. This must be located at the shed, since the Exceptions in 225-32 don't apply.
2. Do I need to replace the 3 lines of 12-2 with a single bigger wire (like 10-3)?
If they are protected by 20A breakers, no, unless they need to be upsized to obviate voltage drop due to length. However, why these a UF cables if they are in conduit is puzzling. 'much easier and cheaper to use individual moisture resistant conductors; e.g., THWN.
3. Do I need a ground rod at the shed?
Yup. See NEC 250-32. You have more than one branch circuit supplying the building: the branch for the 3-lighting, and the MWC.
Note more than one branch or feeder would ordinarily not be permitted, but NEC 225-30(d) specifically permits it in this case; i.e., "control of outside lighting from multiple locations".
Edited 9/18/2006 9:02 pm by BarryO
BarryO,Thanks for responding. A single two-pole 20A breaker in the house now supplies all power to the shed including power to the outside lights which are on the three way switch. The inside and outside lights are powered by one leg and the outlets by the other leg. Do I still need a means of disconnecting all power at the shed, and do I still need a grounding rod at the shed?Thanks,
Tim
Got it. I thought the lights were supplied by an additional circuit. In this case, no grounding electrode required. You still need a disconnect in the shed (can be a 2-pole 20A switch, since this is a residential outbuilding).
Barry,So I need to add a 2-pole switch in the shed near where the power comes in. Is there a standard way of identifying the 2-pole disconnect switch in the shed? That is, should it be a particular color (like red) or style and/or is there a standard way to label it?Thanks again.
Tim
Best would be to get a small disconnect box -- basically what's required now near an outdoor AC condenser unit. These are easily identified, reliable, and lockable.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
In residential outbuildings, "snap switches" (i.e., standard switches) are explicitly allowed. A simple label saying "MAIN" next to it should be enough.
If you use another type of disconnet, it must be labelled "suitable for use as service equipment". In this case, a label of "MAIN" is also appropriate (since it's not really a Service Entrance).
Well, well, well... code details aside, I think you'ld really be happier if you re-do it. Rather than cite chapter and verse, let me explain what would be the preferred way to wire a shed. I say "preferred" because, not only does it comply with most any code interpretation, but will also allow for future needs.
You own situation is complicated by the assorted three-way circuits. Nothing wrong with them as such... I can certainly see where you might want to have to outside light work together with the lights on your house.
When there is a detached building, I always favor buried conduit, with a junction box at each end, where the pipe exits the ground. Why? Because this arrangement allows you to replace the wires later on, without having to dig. I hate digging. I also say dig deep- at least two feet, and cover with sand or pea gravel. Even though you might read the code to allow a lesser depth, the idea is to put the pipe below reach of, say, the gardener when he fixes an irrigation line.
A separate building is also a separate lightning target. As such, a ground rod is always a good thing.
Since you have the three-way circuits, I would run them through a pipe separate from the "power" pipe. At the shed, they would have their own junction boxes, and go their separate ways.
Now, for the shed power circuits. I would first try to guess the maximum amount of power I might need at any one time. 20 Amps? 30? 40?
Personally, I would start with 40 amps and 240 Volts. This would be a two-pole, 40 amp breaker, feeding #8 wires to the shed.
At the shed, I would have the pipe come up the outside, to a disconnect switch. This would feed a small panel inside....there are panels as small as 4 space! These spaces can then feed whatever circuits you might have.
I suggested a junction box outside the shed for both pipes, as all the ground wires ought to be connected to the shed's ground rod- IN ADDITION TO connecting back to the ground rod for the house. (Your 'power' pipe should have a ground wire in it that goes to the house panel for this purpose).
Sure, this sounds like a lot... and also means re-doing what you already have. But I think you will find the convenience, and ease of making changes, make this worthwhile