Change of Plans - Shed Wiring

TXTroyJuly 19, 2011

Thanks to all who responded firstly....(for those of you who haven't seen...see shed wiring in recent post)

Now onto the possible change of plans (plans changed due to advice my bro-n-law received and I'm helping him).

So now he wants to feed his shed (structure separate from the house containing two 20 amp circuits) with one 30-amp circuit from his house using 10 ga wire and installing a subpanel at the structure instead of using a double pole breaker and 12/3 wire.

Questions: 1) Can one 30 amp breaker/circuit run to a subpanel feed two 20 amp circuits?

2) He's gotten the ok to use THHN instead of THWN. The wire will be run in conduit along a deck for part of the way then buried about 15 ft before hitting the shed. People on here say to use THWN, but the two guys he's talked to said THHN is fine. Thoughts?

3) Will that new subpanel in the shed need its own ground rod or is the grounding wire run from the house sufficient?

4) Would you use a single pole or double pole breaker?

5) Where would you put your gfci protector. At house using 30 amp gfci breaker? At subpanel using two 20 amp gfci protectors?

Thanks in advance....as with most other house projects....this seems to keep growing.

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Ron Natalie

1) Can one 30 amp breaker/circuit run to a subpanel feed two 20 amp circuits?
Yes but now he really needs a proper subpanel and grounding system. The exemptions for one circuit (even when bent for MWBC) no longer apply.

2) He's gotten the ok to use THHN instead of THWN. The wire will be run in conduit along a deck for part of the way then buried about 15 ft before hitting the shed. People on here say to use THWN, but the two guys he's talked to said THHN is fine. Thoughts?
Under the deck may not be considered a wet area. Underground conduit IS.
3) Will that new subpanel in the shed need its own ground rod or is the grounding wire run from the house sufficient?
It needs it's own grounding system now (see #1). That is likely to mean TWO ground rods by the way.
4) Would you use a single pole or double pole breaker?
I'm presuming he is running a 240V feeder (the two hot legs + the neutral + ground). In that case he'll need two pole breakers at the house and he needs to be able to disconnect it at the shed with fewer than six handle throws.
Where would you put your gfci protector. At house using 30 amp gfci breaker? At subpanel using two 20 amp gfci protectors?
Every 120V 15 or 20A receptacle in the shed must be protected by GFCI. He can either put a GFCI on those breakers in the shed, or he can use GFCI receptacle(s). The latter will be cheaper most likely.

    Bookmark   July 19, 2011 at 7:17PM
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TXTroy

Thanks RonNat,

Couple Things......

Can you explain the TWO ground rod situation?

Crap, I remember reading about the one circuit exemption but can't remember where. Can you brief me again or too lengthy?

Thanks a bunch.

    Bookmark   July 19, 2011 at 7:25PM
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kurto

If you're going to use a single ground rod, you need to prove that it provides a low enough impedance path to earth. In order to do that, you need to have access to a second ground rod. So, rather than pounding and pulling a second "temporary" rod, you might as well just install two.

The NEC allows only a single circuit or feeder to a remote building. A single circuit (multiwire or not) doesn't require a grounding rod at the remote end, but still requires a ground wire back to the panel. That's the exception that I believe ronnatalie was referencing.

    Bookmark   July 19, 2011 at 9:27PM
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TXTroy

Thanks Kurto.......This is getting pretty involved.

Is it going to much easier to just run THWN (my brother in law actually bought 10/3, but this would work from a 20 amp breaker right??? and have less loss along the run) from a double pole 20 amp gfci breaker to the shed, split the hots (installing a master cut off of course), share the neutral, and call it a day? That leaves the box out of it right and we don't have to mess with additional ground rods.

Is there anything else I'm overlooking?

    Bookmark   July 19, 2011 at 9:56PM
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hendricus

Yeah, with the gfi breaker in the house whenever it trips means a trip to the house, gets really old in a hurry. Put the gfi's where you can reach them without a lot of running or work.

    Bookmark   July 19, 2011 at 10:21PM
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TXTroy

Good Point Hendricus,

One final Q: Since he already bought 10 gauge THWN - Is it ok to use the 10 gauge wire on the 20 amp house breaker that feeds the shed? Is there any transition requirement when we push that 10 ga through and join it with the 12 ga 20 amp circuits in the shed or is it just as if I'm using 12 ga wire the whole run?
Thanks

    Bookmark   July 19, 2011 at 11:12PM
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Ron Natalie

You're always allowed (and sometimes, like on very long runs it's even advisalbe) to put LARGER wire in than the breaker size would suggest. As long as whatever devices (breakers, receptales, wire nuts, etc..) that you're going to stick the larger wire into is sized for that (and I don't think you'll have a problem ehre) it's fine.

The only confusion is that THWN is individual conductors which would need to be run in conduit. Cable usually has designators like UF or NM (which may have individual conductors inside it of THWN). Since you say things like 10-3 (also a designation for a cable), I suspect you have the latter?

    Bookmark   July 20, 2011 at 8:41AM
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normel

Most wire available today carries a dual THHN/THWN rating. Because you are running this in conduit outside (underground or not), you MUST have the THWN rating. Your only options are to use the individual wires in conduit, UF cable, or a combination of both. If your BIL bought and plans to use 10/3, it must be UF (flat, gray covering) and NOT NM (round, orange covering).

    Bookmark   July 20, 2011 at 11:01AM
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TXTroy

Ronnat,

I think now I'm thoroughly confused. If I install a 20 amp DP breaker at the house, run THWN 10/3 from the house, through conduit to the shed, how do I transition from that 10/3 to NM 12/2 to feed those two separate circuits in the shed? I'm pretty sure I need a DP switch, but at what amperage rating and wire config? I know I need a master cut-off in the shed, hence a switch with two poles (for the red and black hots from the 10/3 THWN feeding my two separate NM 12/2 circ), but do you know exactly how the wire config need to look in that junction box with the master cut off?

Incidentally, is there anything wrong with putting one 20 amp receptacle on a 20 amp cir? Meaning that one recept is all the circuit powers? I have a lot of media equip on this one plug.

Thanks,

Troy

    Bookmark   July 20, 2011 at 11:26AM
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hendricus

Just get an equipment disconnect, no fuses or breakers. You can get a double pole. Use GFCI's for each outlet, this way if you trip one nothing else goes off.

    Bookmark   July 20, 2011 at 1:18PM
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kurto

Note: THWN is a designation for individual conductors, which are used inside conduit (10/3 is a designation for a cable, which wouldn't use conduit).

Terminate the THWN 10 gauge wires (and conduit) in a junction box where you'll place the double pole cutoff switch. You can transition to 12/3 NM in this box if you like -- 10 gauge THWN coming in, then the switch, then 12/3 going out. So, black and red go individually through the two poles of the switch, the whites are tied together with a wire nut, and the grounds are likewise tied together with a wire nut or crimp. Don't forget to ground the box (if metal) and the switch.

    Bookmark   July 20, 2011 at 1:19PM
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TXTroy

Thanks Kurto,

I'm messing up the nomenclature.....10/3 and THWN. THWN is running in conduit from the house to the shed. I'm assuming a 20 amp DP switch is the way to go because of the 20 amp breaker at the house the 10 ga THWN is attached to. Is this correct?

Since I'm running two 20 amp circuits in the shed off the 10/3 - I attach the 10/3 black and red to switch upon entering shed, then attach the two blacks from separate 20 amp circ to the switch, wire all my neutrals and grounds (including switch and box)......

Thanks,

    Bookmark   July 20, 2011 at 2:20PM
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kurto

Yes, you'll need a 20A double pole switch to act as a disconnect.

Your wiring plan is fine as long as you keep the hot legs separate throughout the circuit. I usually use 12/3 NM cable, and maintain one hot leg on black and the other on red throughout the circuit. It isn't required, and may not be practical, but it's a reliable way to track that there really are two separate hot legs on this circuit.

    Bookmark   July 20, 2011 at 5:49PM
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TXTroy

Kurto....one thing I left out.....

The two 20 amp shed circuits are wired with NM 12/2. I'm bringing in 10 ga THWN to the master double pole switch, then feeding those two circuits (2 Circuits of 12/2) or black wires. Any problem here?

Question, is it better to use two single pole breakers or one double pole for the 10 ga THWN coming out of the main panel box?

    Bookmark   July 20, 2011 at 6:02PM
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kurto

12/2 NM cable is fine, as long as the breakers are 20A.

You must use breakers that will both trip if either is overloaded. Most of the time, this means a double pole breaker. Depending on the breaker box, you can find clips that will tie the handles together on individual breakers. But, unless you already have the single pole breakers on hand, the double pole will probably be less expensive.

    Bookmark   July 20, 2011 at 6:14PM
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