My plan to run underground wire... is it OK?

[Guido]

120V, 20A breaker at panel.
- 12/3 NMWU through wall to outside of house to a GFCI outlet. Approx 5 ft.
- Run wire alongside house, 24 inches above ground, in PVC conduit fastened to wall.
- At end of house go down to ground level (still in counduit).
- At ground level, exit conduit and run approx. 8 ft. UNDER my deck (basically lying on top of the ground). My deck is about 3 inches off the ground and boards are closely spaced so little chance of damaging wire.
- At end of deck drop down to 24 inches below ground level and run for 20 feet to shed. Again - no conduit.
- At shed, have it come up inside a PVC conduit to an 90 degree LB box into the shed.

Anything wrong with the above?

Also:
1) I know I only need 12/2 but I'd rather run 12/3-wire in case of future expansion. Is it OK to leave one wire unused?
2) I plan on using the GFCI receptacle currently installed on the outside of the house where the wire exits from the basement. (I'd use a GFCI Breaker, but these cost more). Is this OK?
3) If I have enough wire leftover can I use it to wire the inside of the shed? The walls will not be finished (wires stapled to 2X4s with metal boxes).


Any thoughts would be appreciated, thanks!

[Homer]

You must protect the cable with conduit where it exits grade level.

Also, I don't feel that you can stretch the cable unprotected under the deck. Wait for other opinions on the physical damage issue here.

You can use your existing GFCI receptacle if it is a 20A T-slot variety. It can't be the standard 15A with 20A passthru type that would be OK in the US.

You can use 12/3 and have a spare conductor for a future multiwire circuit.

You can use the NMWU cable inside the shed if you wish.

Homer

[Guido]

Thanks again for your help.
Regarding my using 12/3 wire for "future expansion", someone posted the following on another site. It makes sense to me, what do you think?
"The problem with that wire you are leaving unused for the future is that you may never be able to use it. If that hot wire every contains any current at all, the current on the neutral will not match the current on either hot, and the GFCI receptacle will trip instantly. So to ever use that wire in the future, you'd have to remove the GFCI receptacle and install the expensive 20-amp double-pole 120/240 GFCI breaker. As long as you recognize that limitation, it's okay."


I guess I may as well run 12/2. It's no biggie because my panel is full anyway and I doubt I can run another circuit in the future. And I don't even know if I'll ever be able to find a double-pole 120/240 GFCI breaker for my panel :(

[Homer]

Regarding my using 12/3 wire for "future expansion", someone posted the following on another site. It makes sense to me, what do you think?
"The problem with that wire you are leaving unused for the future is that you may never be able to use it. If that hot wire every contains any current at all, the current on the neutral will not match the current on either hot, and the GFCI receptacle will trip instantly. So to ever use that wire in the future, you'd have to remove the GFCI receptacle and install the expensive 20-amp double-pole 120/240 GFCI breaker. As long as you recognize that limitation, it's okay."That quote doesn't tell you the full story. It is true that you can't protect both legs of a multiwire (shared neutral) circuit with two GFCI receptacles. You must use an expensive 2-pole GFCI breaker.

However, if you split the multiwire circuit into two circuits where the neutral is no longer shared, then you can protect those two circuits with one GFCI receptacle on each circuit.

So, you can run one 3-wire multiwire circuit (12/3 or 14/3) into the first box, and splice into two 12/2 or 14/2 cables so the neutral in no longer shared. These two circuits can then be protected by GFCI receptacles.

Homer

[Guido]

So, you can run one 3-wire multiwire circuit (12/3 or 14/3) into the first box, and splice into two 12/2 or 14/2 cables so the neutral in no longer shared. These two circuits can then be protected by GFCI receptacles.
Homer
But by doing this I will have the 60 foot wire running to the shed non GFCI protected correct? Is this OK?

And just to clarify, your other post (in the kitchen wiring thread) states that this method is NOT permitted in kitchen counter receptacle wiring for a 15A circuit correct? That I either need to run 20A circuits, or use a double-pole GFCI breaker.

Thanks again for all your help, and sorry for the million questions. Just last night I bought the Electrical Code Simplified book and hopefully I'll be bothering you guys a lot less :)

[Homer]

But by doing this I will have the 60 foot wire running to the shed non GFCI protected correct? Is this OK?This is OK. You must make sure that you protect the cable from damage by burying it deep enough (check your new book) and/or using conduit. While it is preferable to GFCI protect the entire outdoor cable run it is not a code requirement.

And just to clarify, your other post (in the kitchen wiring thread) states that this method is NOT permitted in kitchen counter receptacle wiring for a 15A circuit correct? That I either need to run 20A circuits, or use a double-pole GFCI breaker.Yes, the kitchen counter receptacles must follow very specific code requirements. Kitchens meeting the older requirements now create a problem for those wishing to simply add GFCI protection to the existing split receptacles.

Homer

[Unregistered]

Thank you very much for all your help.
I have one more question (for today :) )

Since the cable won't be GFCI protected, I've decided to go the entire run in PVC conduit - even the buried section. I've also decided to go with 12/3 cable.
What cable should I use in the conduit (I'm not sure if NMWU is OK) and what size PVC conduit should I buy?

[Homer]

I've also decided to go with 12/3 cable. What cable should I use in the conduit (I'm not sure if NMWU is OK) and what size PVC conduit should I buy?I would recommend against using the NMWU in conduit. If you do this you will need to use 1" PVC conduit for 12/3 NMWU.

I would use individual conductors in 1/2" PVC conduit. You can pull #12 black, red, white and green conductors. They will be T90/TWN dual rated which is equivalent to THHN/THWN dual rated in the US.

Take a look at this thread for pointers on making a transition between cable in the house and shed and the individual conductors in the conduit.

Homer

[Guido]

Thank you, that's exactly what I'll use, and wire it as you mentioned in the other thread.

Do I need to use a slip joint (or whatever it's called) between the ground/structure transition for frost heaves? I read this somwhere but I couldn't find it at HD (I should have asked).

Are T90, THHN, THWN, etc. acronyms?

[Homer]

In Canada the conductors that are rated for use in conduit are designated as T90 for dry (indoor) and TWN75 for wet (outdoor) applications. Typically the wire will be dual rated T90/TWN75. As the designations suggest, the ratings are 90°C and 75°C.

In the US the conductors that are rated for use in conduit are designated as THHN for dry (indoor) and TWHN for wet (outdoor) applications. Typically the wire will be dual rated THHN/THWN. Likewise, the ratings are 90°C and 75°C.

Take a look at this link (http://www.kltannehill.com/Technical%20Documents/Popular%20Wire%20Designations.htm) for some designations. The T90 is not shown but T is for Thermoplastic.

As for expansion joints or fittings, wait for others to comment.

Homer

[mdshunk]

Don't know anything about a requirement for the expansion couplings in your area. What I can say is that it's a darned fine idea, especially if the conduits don't rest on virgin soil. The expansion couplings are a little pricy (50 bucks for a 3"), but worth every penny in my opinion. Just make sure that you have a smidge of slack in each end of the wire (not made up tight), so that if the conduit does move a little, it won't rip the wires off the terminals. I seriously doubt that you'll find an expansion coupling at a local home center. Home centers only have the material you need to do a barely acceptable job, and not a fine job. You'll likely have to stop in an electrical supply house to get one.

[Guido]

Thanks for the wire definitions Homer - it makes it easier to remember when you know what the acronyms mean.

As for the expansion joint - they're that much eh? In my book they look like a couple plastic pipes , one fit into the other, with an o-ring sealing the two. I expected a couple bucks. I'm going to ask around if it's a requirement in my area.
On a side note, I don't understand why it's not a requirement in every area - all it takes is the structure or soil to move 1/4" and what will happen to the conduit and LB fitting? Something has got to give.


I really need to find an electrical supply house near me - I once thought Home Depot to be the answer to all my home renovating problems, but lately that has not proven so.

[Guido]

I just thought of something - if I convert my exterior receptacle to 20A, does that mean according to code I can't use any of my 15A extension cords?

[Homer]

If I convert my exterior receptacle to 20A, does that mean according to code I can't use any of my 15A extension cords?You can still use a 15A extension cord.

Homer

[Guido]

I would use individual conductors in 1/2" PVC conduit. You can pull #12 black, red, white and green conductors. They will be T90/TWN dual rated which is equivalent to THHN/THWN dual rated in the US.
OK a couple dumb questions here:
T90/TWN wire is only sold individual (not in a sheath)?

My original plan was to run 12/3 cable for possible future expansion (I really only need 12/2). But since I'm now running individual wires, can I only run the two that I need (black, white) and IF I need to expand in the future I'll run the red wire at that time? It is quite possible that this extra wire will sit unused for years and it'll only be a waste of money.

[Homer]

OK a couple dumb questions here:
T90/TWN75 wire is only sold individual (not in a sheath)?Yes, it is wire and not cable and you will find it sold by the foot or meter.

My original plan was to run 12/3 cable for possible future expansion (I really only need 12/2). But since I'm now running individual wires, can I only run the two that I need (black, white) and IF I need to expand in the future I'll run the red wire at that time? It is quite possible that this extra wire will sit unused for years and it'll only be a waste of money.Sure, but don't forget the third green wire for the EGC. You need a minimum of black, white, and green(or bare). Personally, I would spend the extra $5 or $10 and pull all 4 wires at once.

Homer

[Guido]

I didn't see the wire, only cable - I guess I should take a closer look next time. Or ask someone! You're right, for $5-$10 it's worth putting in the extra wire. And I won't forget the ground wire - thanks!

You mentioned 1/2" conduit, some people here said go 3/4" since it's easier to pull the wire, and I'll be glad if I ever decide to run larger wires. I priced them both out and they're very close in price (actually, a 3/4" LB fitting is cheaper than a 1/2"!).
I couldn't find in P.S. Knight's book where it says what's the largest awg wire you can fit in a certain conduit size. I'm wondering what's the maximum amperage I can run through a 3/4" vs 1/2" conduit.

[Guido]

Finally I got some good weather on the weekend and dug the trench. It took me about 4 solid hours with a pick and a shovel, but it came out good. I installed the conduit and hopefully one of these evenings I'll run the wire.
I didn't install a pull string in the conduit because I was working in the dark and I couldn't find the string inside the shed without any lights. But I do have a 60' electrical fish and I installed 48' of conduit, so hopefully it won't be a problem to use that.

I bought the stuff from HD, I didn't know the T90/TWN wire was multi-strand - is 12/2 loomex multi-strand also?

They didn't have enough red wire so the guy sold me blue instead and said it makes no difference. Does it matter?


I didn't run the conduit exactly as I had hoped. Originally I planned to run it from the shed to the house, then along the side of the house (above grade) to the front, then inside the house to a 20A breaker in the panel.
I don't know when I'll get around drilling the hole in the concrete and freeing up a 20A breaker in the panel, so for now I ran it from the shed to the house, then instead of turning right to go to the front, I turned left and went 8' to an outdoor receptacle and I just teed off from the existing circuit. There is nothing else on this circuit. I know it's only 15A, but it'll do for the winter. Then in the spring when I drill the hole and install the breaker I'll run some new conduit to the front of the house. The only problem is the wire won't be long enough so I'll have to install a junction box to splice longer wire.
And that's where I'm at.

Thanks for all the help here - it really saved my ***. The guy at home depot was a little ****ed that I didn't take his advice when he said I require #10 loomex in a 1/2" conduit to run 15A for 50 feet. He was saying something about every 50' you go to the next larges AWG wire, and for outdoors you go another step larger. A month ago I would have taken his advice, but luckily I found you guys! Thanks!!!

[Homer]

I bought the stuff from HD, I didn't know the T90/TWN wire was multi-strand - is 12/2 loomex multi-strand also?The #12 cable is solid.

They didn't have enough red wire so the guy sold me blue instead and said it makes no difference. Does it matter?Sure, anything but white or green.

The guy at home depot was a little ****ed that I didn't take his advice when he said I require #10 loomex in a 1/2" conduit to run 15A for 50 feet. He was saying something about every 50' you go to the next larges AWG wire, and for outdoors you go another step larger.For a 50' run, #12 @20A and 30°C ambient gives a voltage drop of 2.7% which is acceptable. Most tables and calculators use an unrealistically high 75°C for ambient temperature instead and the figure works out at 3.2%.

If you were going much further then you would benefit from an increased gauge.

Homer

[Guido]

Update:
I was supposed to borrow my father in-law's fish to pull the wire but he couldn't find it, so Saturday I went to HD and bought my own.
Finally I have everything I need to get it done!

So I'm starting to pull the wire through and something doesn't look right. I unroll the wire on the ground and guess what... it's too short! That can't be because I measured the run to 16 meters and and ordered 18 meters to be save. I watched the guy put it through the "winding machine" and saw the dial go up to 18m. He gave me 19m to be safe. So I should have 3 extra meters. I measured the wire on the ground and it came out to 9.4 meters!!! Less than half.

So on Sunday I returned to HD and bought another 18M and insisted they measure it with a tape measure (I didn't trust that machine). People were wondering why we had 18M of wire pulled down the aisle.

I got home, pulled the wire throught without a problem, and everything was perfect - until I went to connect it to the existing outdoor receptacle. The box wasn't big enough for the extra wire caps, so I need to return to HD to get a bigger box. Hopefully I'll be done sometime this week.

Is it me or is it a major PITA to connect multi-strand 12GA to the screw terminals on a receptacle? The strands keep getting "squished" out and it looks like crap.

Also, when installing the first metal receptacle box on the inside of the shed (where the wire enters) I could not find a box that has a conduit punch-out hole on the back AND the cable clamps for the sheathed wire to exit on the sides. It has either one or the other, but not both. So I bought the box with the clamps and drilled a hole on the back for the conduit to fit through perfectly.
For sure there is an easier way, but I had no choice.

[Homer]

Is it me or is it a major PITA to connect multi-strand 12GA to the screw terminals on a receptacle? The strands keep getting "squished" out and it looks like crap.You should use crimp connectors if you're having trouble with the strands.
http://www.rpelectronics.com/Data/1723DP.JPG

Homer

[Unregistered]

Thank you! I bought a box of 40 at HD. Regular $8.49, they were on clearance special for $2.00. Sometimes good deals can be had there.