I’m running power to my shed and I’ve got a few questions that I’m hoping somebody could help me with. Here’s an overview:
I’m doing a subpanel at the shed. Distance from the main panel (at the house) to the shed is about 100’. Using 10/3 wire (two hots, a neutral, and a ground).
Why such light-duty wire for the feeder cable? It seems to me that if this is worth doing at all, it's probably worth doing in a manner which will not put so severe a crimp in what you can run in that "shed". Further, if (as I suspect) that "10/3 wire" is run-of-the-mill NM-B, how are you planning to get it across that 100-foot gap between the house and the shed? NM-B is
NOT rated for underground use, even in conduit.
At the main service panel I have a double-pole 20-amp breaker.
Even with the light feeder cable, you could go to 30A here without creating a huge problem, at least presuming your measurement is accurate. Technically, this will produce just slightly over the 3% maximum recommended voltage drop at full load; but it is
SO close that I would not lose sleep over it.
At the shed: I have a subpanel for two circuits, either two 20's or a 15 and a 20.
Exactly what loads do you intend to run off these breakers?
I have two 8’ ground rods, 6' apart, connected with #6 wire.
These are my questions:
1) Grounding at the shed Part 1 - Where do I connect the #6 to the subpanel?
To the Ground bus bar inside the panel; and
NOT to the Neutral bus bar, which in turn should
NOT be bonded to the Ground (you may need to remove a pre-installed bonding screw to accomplish this, and/or possibly even purchase an accessory part to implement the separate Ground & Neutral busses).
2) Grounding at the shed Part 2 - What do I do with the ground that’s coming from the main panel (the bare wire in the 10/3 “feed”)?
It too connects to the Ground bus bar.
I don't think it's supposed to be connected to the subpanel, is that right?
No. Wrong.
Should it be connected at the main panel (that wouldn't make much sense to me)?
It needs to be properly connected at BOTH ends.
3) At the shed, should I get a subpanel with a main breaker, one switch that will shut the whole thing down? That seems like overkill if I only have 2 circuits, but I’ve seen it mentioned a few places.
With six or fewer branch circuit breakers in the sub-panel, you are not required to provide a "Local Disconnect". That said, it's not prohibited either; and IMCO, it remains a good idea in any case.
4) GFCI – if I put an outlet on the outside of the shed, does the outlet need to be GFCI, or the breaker, or both?
Not "both". The outlet needs to be "GFCI-protected". That protection can be supplied by
either an integrated GFCI-type outlet,
or a GFCI breaker.
Thanks very much for any guidance you can provide. I live in North Carolina, FWIW.
You're welcome. But do note that my answers above are NOT geographically specific (save for being USA-centric), and local codes can always override the NEC. So when in doubt, it's always best to check with YOUR local inspector or permit office.
Check your local codes for information about the additional ground rods for your shed. Some codes (inspectors) don't want another ground rod on a residential service.
AFAIK, historically the second set of ground rods were not always required, but were never prohibited. And they HAVE been required for awhile, now.
Your subpanel (every subpanel) will require a ground bar separate from the neutral bar, and the neutral bar should not be bonded (electrically connected) to the panel or to the ground bar. The ground bar is bonded to the panel. You may have to purchase the ground bar, the last one I bought was a few bucks. They look about identical to the neutral bar. If the panel manufacturer supplies a neutral bonding screw, (usually these are green) don't use it on a subpanel.
The ground wire from your 10/3 connects to the ground bar along with all the ground wires from your circuits.
The neutral from your 10/3 connects to the isolated neutral in your panel along with all the neutral wires from your circuits.
Exactly correct.
I prefer the idea of one main breaker to shut down the entire remote panel, but with only two circuits that may be overkill!
Agreed.
I suggest a ground fault receptacle for each receptacle you want regardless of inside or outside. They have come down in price a lot.
Regardless of cost, more than one per branch circuit is a total waste, assuming you wire things correctly.
At the main panel, the 10/3 neutral connects to the neutral bar there, and the ground connects to the ground bar there.
Also correct.
I know the separation of ground and neutral in a sub panel is a confusing issue and not intuitive, but it has been this way for many years and is often installed incorrectly.
I agree that this topic seems to foster a lot of confusion; but I really don't understand why. Neutral and Ground are two different things; and BOTH are required, period. It really is that simple.
