Another Shed Wiring question

[Gofor]

Pulled the electrical permit for wiring my shed/shop today, but have a couple questions:

The wiring will be stranded AWG12 THHN run in EMT. I plan to have two 20A circuits for the North and West walls (alternating outlets), and another two for the east and south walls. If I understand the NEC, I can use a shared ground wire for the two circuits on the same walls as long as the grounding wire is equal in size to the largest conductor. Is this correct?

If I do the above, could there be a problem with nuisance tripping of the GFCI protection on each circuit? I plan for the GFCI will be the first outlet on each circuit instead of a GFCI circuit breaker, mainly due to cost. Both hot and neutral line and load will flow through the first outlet, but the remaining outlets will be "Tee'd" off the circuit by dropping down from the main conduit running along the wall top plate.

Go

 

[Gotcha6]

For the difference in price and the aggravation it would cause NOT to do it, just run separate neutrals. In addition to the requirements you mentioned, you would also be required to tie the 2 shared circuits together (i.e 2 pole breakers) in the panel. If one trips, the other does also. Is that what you really want? Not doing this on a shared neutral results in a hazardous condition if you ever needed to service one circuit and failed to turn off the other as well.

 

[FredP]

not an electrical genius but I question the use of stranded wire versus solid wire.:icon_scra

 

[Skymaster]

fred, when running thru conduit it is normal to run stranded individual wires, easier to pull, no jacket needed, etc

 

[FredP]

fred, when running thru conduit it is normal to run stranded individual wires, easier to pull, no jacket needed, etc

Thanks Jack. Never noticed that in commercial work.

 

[Gofor]

For the difference in price and the aggravation it would cause NOT to do it, just run separate neutrals. In addition to the requirements you mentioned, you would also be required to tie the 2 shared circuits together (i.e 2 pole breakers) in the panel. If one trips, the other does also. Is that what you really want? Not doing this on a shared neutral results in a hazardous condition if you ever needed to service one circuit and failed to turn off the other as well.

Shared ground, not shared neutral: ie. I am planning on running one AWG12 ground wire to serve both circuits. There will be individual neutrals for each circuit. You are absolutely correct on me not wanting to do shared neutrals.

 

[Gotcha6]

My bad. Shared ground is okay. The THHN will be an easy pull too, as the outer jacket is not PVC but a slick poly to help it along.

 

[Skymaster]

Fred even when they hooked up my house generator, electrician ran 300 ft of individual wire,in red,white black, believe it is called thnn wire,stranded wire for flexibility

 

[ehpoole]

not an electrical genius but I question the use of stranded wire versus solid wire.:icon_scra

Stranded wire is generally the better choice for fishing through conduit and there is nothing wrong with the use of stranded wire, both will carry electricity equally well, and you can easily find receptacles and switches that will readily accept stranded wire if you buy the better grades of such or you can simply crimp suitable lugs onto the wire and secure the wires with bolts.

 

[Gotcha6]

Stranded wire will usually run cooler because the majority of the electricity travels along the surface of the wire. With more circular area, the easier for it to pass with less resistance.
The only caveat I could see to using stranded wire in any application would be a corrosive atmosphere (swimming pool pump room) where the conductor may start to fail in a connector due to the corrosion. I'm sure precautions could be taken in such a case. Just my opinion on that.

 

[petebucy4638]

Keep the two branch circuits completely separate from each other. I have never liked the concept of sharing grounds or neutrals between branch circuits. It makes sorting out electrical problems all the more complex.

Pete

Pulled the electrical permit for wiring my shed/shop today, but have a couple questions:

The wiring will be stranded AWG12 THHN run in EMT. I plan to have two 20A circuits for the North and West walls (alternating outlets), and another two for the east and south walls. If I understand the NEC, I can use a shared ground wire for the two circuits on the same walls as long as the grounding wire is equal in size to the largest conductor. Is this correct?

If I do the above, could there be a problem with nuisance tripping of the GFCI protection on each circuit? I plan for the GFCI will be the first outlet on each circuit instead of a GFCI circuit breaker, mainly due to cost. Both hot and neutral line and load will flow through the first outlet, but the remaining outlets will be "Tee'd" off the circuit by dropping down from the main conduit running along the wall top plate.

Go

 

[Jeremy Scuteri]

GFCI circuits ensure that the current on the hot wire matches the current on the neutral wire. Sharing neutrals would cause them to trip, sharing grounds would not pose any issues for the GFCI circuits.

 

[ehpoole]

GFCI circuits ensure that the current on the hot wire matches the current on the neutral wire. Sharing neutrals would cause them to trip, sharing grounds would not pose any issues for the GFCI circuits.

That is one of those "yes and no" things as it is both correct and incorrect. Whether the shared neutral will create any issues depends entirely upon where in the circuit you are introducing the GFCI. You can't share the neutral after the GFCI (whether that be a GFCI circuit breaker or inline receptacle), but you certainly may share the neutral prior to the GFCI without any issue. If one then wanted to continue using the shared neutral downstream and GFCIs are required (such as with a garage shop) then you would simply opt to install a GFCI receptacle at every outlet location rather than the usual single GFCI upstream and passing it through to ordinary receptacles downstream (GFCI receptacles are inexpensive enough these days that such is certainly an option). The other option, of course, being to run separate neutral and hot wiring to every downstream receptacle on the circuit, though that may come at the expense of one or two (if using Romex) extra conductors being introduced so you must have enough allowance in the conduit and box fill ratios to accommodate the added wires (which depends heavily upon how many other conductors you may have also sharing the same raceway, such as those bound for other circuits or lighting).

 

[Jeremy Scuteri]

That is one of those "yes and no" things as it is both correct and incorrect. Whether the shared neutral will create any issues depends entirely upon where in the circuit you are introducing the GFCI. You can't share the neutral after the GFCI (whether that be a GFCI circuit breaker or inline receptacle), but you certainly may share the neutral prior to the GFCI without any issue. If one then wanted to continue using the shared neutral downstream and GFCIs are required (such as with a garage shop) then you would simply opt to install a GFCI receptacle at every outlet location rather than the usual single GFCI upstream and passing it through to ordinary receptacles downstream (GFCI receptacles are inexpensive enough these days that such is certainly an option). The other option, of course, being to run separate neutral and hot wiring to every downstream receptacle on the circuit, though that may come at the expense of one or two (if using Romex) extra conductors being introduced so you must have enough allowance in the conduit and box fill ratios to accommodate the added wires (which depends heavily upon how many other conductors you may have also sharing the same raceway, such as those bound for other circuits or lighting).

The neutral before the GFCI circuit is just that *BEFORE* the GFCI circuit and therefore NOT part of it. Putting separate GFCI circuits at each receptacle just creates a bunch of separate GFCI circuits, again the neutrals will not be shared by definition since each neutral is on a separate GFCI circuit at that point.

Still a good thing to clarify though.

The GFCI circuit ensures the OUTGOING hot wire current (out of the GFCI) matches the RETURNING neutral wire current (flowing back into the GFCI). If these don't match, the GFCI will trip. By sharing the neutral you allow the return current to be split among multiple paths so all of it won't have to flow back to the GFCI circuit that provided the hot current. The GFCI senses the mismatch and trips the circuit.

 

[Gofor]

And so it begins: EMT on the first wall mainly done.

I ran a test bundle of 5 solid wires through a couple runs. I was able to push the wire through without needing a fish tape, and it will be easier to connect to the outlets, although a little more difficult to fold into the box. There will only be five wires in the conduit on three walls unless I also run a 220 circuit (still deciding that one). I still need to run a test with the solid on some 3/4" conduit as I will have nine wires running to the east wall from the breaker box, and ten in one short section. May opt to just go with two 1/2" conduits instead of one 3/4", but will have to go up to 3/4 on at least one if I add 220.

I am running a shared ground. With the "new" requirement that every box has to be grounded, as well as every device (fixture/outlet), a second wire would just be redundant.

The GCFI will be the first outlet on each of the five outlet circuits.

My biggest surprise so far is the limited choices of materials at Lowe's. Because I am running multiple circuits in the same conduit(s) I would like to use alternate colors for hot and neutral. I can get black, red, and blue for the hot (although in one run I would also like to have orange), but they do not carry gray for an alternate neutral color. The biggest limitation, though, is in their conduit. For the outside feed, I need either schedule 80 NMT (PVC) or RMT (Rigid metal tubing) for the above ground sections running up to the main house box and up the side of the shed. Lowe's here carries neither.

So, off to the electrical supply house this week. In Florida, most supply houses would not sell retail; only to contractors. I hope that isn't the case here.

Go

 

[bowman]

Check worth Graybar or other suppliers for a better choice of materials.