Shed wiring project + generator

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  #1  
Old 03-29-13, 01:02 PM
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Shed wiring project + generator

I'm planning to wire my shed this spring. I've done a lot of reading, so I think I have most of my plan put together. I'd like to see if there's anything I'm doing that is not appropriate, or could be better.

Details:
The shed is 100' from the house
Wiring will leave the house 50' from the main panel
I plan to run 50A service to the shed for future use (potentially a pool)
Short term will only be used for lights and minor 120V shop appliances (compressor, table saw, chop saw, etc.)

Inside:
50A DP breaker on the main panel
6/3 NM-B to the exterior wall
Connections made in LB body at house

Outside:
1" schedule 40 PVC, buried >= 18" deep
3x 6AWG THHN in the conduit *
1x 10AWG Green THHN in the conduit (GND)
*Can all 3 be black marked with Red/White markings on the ends of two of them? My local supply shops don't sell Red/White by the foot.
Second 1" conduit for CAT5e/RG-6... why not if I'm already digging...

Shed:
Sub-panel with 50A main breaker
2x 8' GND rods, likely buried at 45 degree angle due to bedrock
GND rods connected by uninsulated #4

Generator:
If I want to hook up the generator in the shed, is there any way to do this?
 
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  #2  
Old 03-29-13, 02:16 PM
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Connections made in LB body at house
Best to use a 4x4 junction box so you have room the connections. Some conduit bodies do not have the cubic inches stamped in and can't therefor by code be use for connections. Doubt the cubic inces even if marked would be enough.

Can all 3 be black marked with Red/White markings on the ends of two of them?
#6 and smaller can't be redesignated white. You don't need a red and black. Two blacks are fine.

Sub-panel with 50A main breaker
Does not need to be a 50 amp breaker. Would suggest a 100 amp main breaker panel so you have enough spaces. The 100 amp breaker that comes with it is fine because it is only used as a disconnect. You will need to buy and install a ground bar.

Generator:
If I want to hook up the generator in the shed, is there any way to do this?
Is that to power the shed only?
 
  #3  
Old 03-29-13, 06:29 PM
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Best to use a 4x4 junction box so you have room the connections. Some conduit bodies do not have the cubic inches stamped in and can't therefor by code be use for connections. Doubt the cubic inces even if marked would be enough.
Thanks. What is the required space for connecting 3 pairs of #6 and 1 pair of #10?

#6 and smaller can't be redesignated white. You don't need a red and black. Two blacks are fine.
OK, so I need to find #6 white in order to be to code, thanks. If it were #8, redesignated would be OK? Seems illogical...

Does not need to be a 50 amp breaker. Would suggest a 100 amp main breaker panel so you have enough spaces. The 100 amp breaker that comes with it is fine because it is only used as a disconnect. You will need to buy and install a ground bar.
Thanks. Ground bar needs to remain isolated from neutral, correct?

Is that to power the shed only?
No, I was hoping to use the generator to back power the house, but can't come up with a way to do it that involves a transfer switch. My other option is to install a transfer and port on the house, but would have been more convenient to just leave the generator in the shed. Any ideas?
 
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Old 03-29-13, 07:28 PM
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If it were #8, redesignated would be OK? Seems illogical...
No wire #6 or smaller can be redesignated as a neutral or ground. Since #8 is smaller then #4, smallest wire that can be redesignated as ground or neutral, it can't be either.

Thanks. Ground bar needs to remain isolated from neutral, correct?
Almost. The ground bar is bonded to the panel. The neutral bar is isolated from the panel and not connected to the ground bar. Ground wires of branch circuits are only landed on the ground bar and neutrals only on the neutral bar.

I can't think of a way to use the shed feed for a generator. Maybe the pros can, Simplest is a second set of wires.
 
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Old 03-29-13, 08:00 PM
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Inside:
50A DP breaker on the main panel
6/3 NM-B to the exterior wall
No. A pool's feed must be piped the whole way. The ground must be copper and insulated.

The good news:
In pipe #6 Cu is good for 60A with a #10 ground and 70A with a #8 ground.

With enough 240V loads, the neutral does not need to be bigger than the ground.
 
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Old 03-29-13, 10:30 PM
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Connections made in LB body at house
What ray2047 said, and: In the old days you were not allowed to use a wire nut to splice the ground to the pool. Each end had to be under it's own screw. I'd use a five hole ground bar, no tape, and just let it float in the junction box. I don't know how the inspectors are interpreting the new wording in that section of the code. It makes little sense to me. 680.25(B)
Outside:
1" schedule 40 PVC, buried >= 18" deep
The local inspectors decided that any exposed PVC was subject to physical damage. This required us to use sch 80 down the wall to 18" depth. Then switch to sch 40. The '11 code decided that sch 80 was not sufficient for a physical damage location for pools. Only rigid (RMC) or intermediate (IMC) are allowed. You can still convert to sch 40 below 18" depth. 680.25(A)(1)
3x 6AWG THHN in the conduit *
1x 10AWG Green THHN in the conduit (GND)
Pipe outside is defined as a wet location. Use only wires with a W in the rating, like THWN.
GND rods connected by uninsulated #4
#8. If protected where exposed, with PVC pipe.
Generator:
If I want to hook up the generator in the shed, is there any way to do this?
Not for less money than ray2047's idea of a second set of wires.
 

Last edited by Glennsparky; 03-29-13 at 11:54 PM.
  #7  
Old 03-30-13, 12:02 AM
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... The ground must be copper...
My mistake. The ground can be aluminum or copper between breaker panels. It seems it's after the last breaker panel that it's copper grounds only.
 
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Old 03-30-13, 04:01 PM
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The shed is 100' from the house
Wiring will leave the house 50' from the main panel
With a run that long I'd use larger conductors to decrease the voltage drop. Plus, by going to #4 AWG you can designate the black wires with tape and avoid having to buy wire with red or white insulation. My $0.02.

Second 1" conduit for CAT5e/RG-6... why not if I'm already digging...
Third 1" conduit for the feed from the generator to the house... why not if you're already digging?

Originally Posted by Glennsparky
A pool's feed must be piped the whole way... The '11 code decided that sch 80 was not sufficient for a physical damage location for pools. Only rigid (RMC) or intermediate (IMC) are allowed. You can still convert to sch 40 below 18" depth. 680.25(A)(1)
It sounds like you're just feeding the subpanel with this run, and that you'll feed the pool equipment from the subpanel. If so, then the special requirements for the wiring methods for pools should only apply as yor install that run; i.e., from the subpanel to the pool.
 
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Old 03-31-13, 04:51 PM
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Alright, so far, my takeaways:
1 - Generator needs to be it's own wires back. Two questions:
a - Does it need it's own neutral? GND?
b - Is it necessary for it to be in it's own conduit?
Third 1" conduit for the feed from the generator to the house...
2 - The schedule 40 is OK as it's going to the shed. Future run to pool from shed would need to be RMC/IMC.
It sounds like you're just feeding the subpanel with this run, and that you'll feed the pool equipment from the subpanel. If so, then the special requirements for the wiring methods for pools should only apply as yor install that run; i.e., from the subpanel to the pool.
3 - THWN - got it. Was planning on this anyway. Home Depot wire calls itself THHN, but it's really THHN/THWN-2.

4 - Can't redesignate as white unless I bump up to #4 wire (may not be a bad idea for voltage drop anyway.

Now, a few more questions:
If I were go to what I consider the opposite extreme, and decide to only run 20A on a GFCI (screw the pool & generator):
1 - I only need to bury to 6", no conduit if UF-B, correct?
2 - Is there anything against putting it in a conduit anyway?
3 - Can I run as big a wire as I want (eg. #6), as long as the breaker in my main panel is 20A, GFCI?
4 - Can I run two sets of wires (eg. 2x 6/2) so I have 2x120V (not 220V), or does that bring me back to being 18" and conduit?
 
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Old 03-31-13, 05:49 PM
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a - Does it need it's own neutral? GND?
It needs it's own neutral. It can share a ground if in the same conduit. Ground (EGC) is sized to the largest load.

b - Is it necessary for it to be in it's own conduit?
No. See preceding answer.

1 - I only need to bury to 6", no conduit if UF-B, correct?
No. 24" with one exception. If the line is GFCI protected it can be one foot. RMC (threaded ridged metal condut) is about the only thing that can be buried 6"

2 - Is there anything against putting it in a conduit anyway?
If you mean cable, best practice is not to run cable in conduit except to sleeve it for protection where it enters and leaves the ground. Pulling #6 UF-b through conduit would be a real challenge.

3 - Can I run as big a wire as I want (eg. #6), as long as the breaker in my main panel is 20A, GFCI?x
Yes but it probably won't fit the breaker so you will need to pigtail yje hot to a smaller wire. White and ground should not need to be pigtailed.

Can I run two sets of wires (eg. 2x 6/2) so I have 2x120V (not 220V), or does that bring me back to being 18" and conduit?
You never left that. You could run a multiwire circuit that would give you two 120v 20 amp circuits. You would need red, black, white, ground. "Can I run two sets of wires (eg. 2x 6/2) so I have 2x120V" No, you can not run two branch circuits. The multi wire counts as one branch circuit. It would be connected to a 20a 240 breaker or two handle tied 120v 20a breakers on opposite legs of the 240.
 
  #11  
Old 03-31-13, 06:41 PM
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Ray -

Thanks for all the answers, again!

I was unclear in one (possibly many, but you sifted through it), so let me ask a different way:

What are the limitations to when I only need to bury the cable 12" deep?
I understand that it needs to be GFCI protected, and I would go with UF-B direct burial. Am I only allowed a 120V/20A (max) circuit, or could I run 220/240V, 20A.
 
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Old 03-31-13, 07:33 PM
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Am I only allowed a 120V/20A (max) circuit, or could I run 220/240V, 20A.
See post #10. The answer is that
Originally Posted by ray2047
You could run a multiwire circuit that would give you two 120v 20 amp circuits. You would need red, black, white, ground... The multi wire counts as one branch circuit. It would be connected to a 20a 240 breaker or two handle tied 120v 20a breakers on opposite legs of the 240.
 
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Old 04-01-13, 05:45 PM
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In looking at the 2011 NEC, Table 300.5 Column 4 is:
Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes
Although I would love to be able to run the multi-wire, this is why I was hesitant.
 
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Old 04-01-13, 10:01 PM
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What are you trying to power? A multiwire 20A branch circuit is a 20A 240V circuit, plus a neutral, or it's two 20A 120V circuits. It just can't be both.

List the loads you need to power and we can come up with the service needed.
 
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Old 04-02-13, 10:03 AM
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Nashkat -

I don't have a good definition of what loads - but likely just various tools/radio, and some lighting.

My recent question was because I would like to maximize the power/effort ratio. If I'm digging a 110', 12" trench and I can only run 120V/20A, so be it. If I can run twice as much power at the same depth (effort), I will.

Going to 18" will be an issue with roots, rocks, etc. that I'd like to avoid. It also adds the additional work/cost of a conduit, unless I go to 24", which will be even more roots, rocks, etc.

So, my question still stands (but I think 300.5 answered it): Is 120V/20A with GFCI breaker the max I can run at a depth of 12" (putting aside RMC/IMC), or is a multi-wire config still compliant to code?
 
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Old 04-02-13, 10:28 AM
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Yes, that is the way I read table 300.5(2008).

I always use a Sawzall with a 12" wrecking blade when I dig. Doesn't do a thing for rocks but sure goes through roots. You can actually stick it in the gound and cut a path for you digging.
 
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Old 04-02-13, 10:48 AM
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Without getting my code book out and looking up the referenced article I am going to state that a multi-wire branch circuit supplied through a two-pole, 20 ampere GFCI circuit breaker may indeed be laid in a trench with only 12 inches of cover. In almost all cases when the code states a voltage it is voltage to ground and a 240 volt circuit still is only 120 volts TO GROUND.
 
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Old 04-02-13, 01:23 PM
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Going to 18" will be an issue with roots, rocks, etc. that I'd like to avoid. It also adds the additional work/cost of a conduit, unless I go to 24", which will be even more roots, rocks, etc.
Going deeper does not invoke a need for conduit, it decreases the need. For example, you can run power without GFCI protection just 6" underground in either rigid or intermediate metal conduit (RMC or IMC).

I don't have a good definition of what loads - but likely just various tools/radio, and some lighting.

My recent question was because I would like to maximize the power/effort ratio.
Best guess, if you're unwilling or unable to calculate the load, is that a 30A 120/240V subpanel will best meet your needs. For the effort involved I'd probably make it a 60A while I was doing and have plenty of capacity for the future.

If you don't need any 240V power in the shed, the GFCI-protected cable you're thinking of burying can be used for a multiwire branch circuit. Just make it 12-3/G Type UF.
 
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Old 04-02-13, 04:02 PM
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Yes, that is the way I read table 300.5(2008).
Without getting my code book out and looking up the referenced article I am going to state that a multi-wire branch circuit supplied through a two-pole, 20 ampere GFCI circuit breaker may indeed be laid in a trench with only 12 inches of cover. In almost all cases when the code states a voltage it is voltage to ground and a 240 volt circuit still is only 120 volts TO GROUND
OK, so you both interpret the code to say that a multi-wire branch circuit with a 20A double-pole GFCI breaker and UF-B cable burried at 12" is compliant. Great! This is the path I will take.

If you don't need any 240V power in the shed, the GFCI-protected cable you're thinking of burying can be used for a multiwire branch circuit. Just make it 12-3/G Type UF.
I'll be getting 8/3 UF, only because of the length of the run and voltage drop.

With my configuration of a multi-wire branch circuit, what are the grounding requirements for the shed? Does it still require 2 ground rods, etc. or was that only when I was bringing larger service and a sub-panel?
 
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Old 04-02-13, 04:08 PM
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The additional grounding at the shed is for a subpanel; you won't need that with the multiwire circuit.

a multi-wire branch circuit with a 20A double-pole GFCI breaker
The better way to protect the two circuits is with two single-pole breakers with their handles connected with a handle tie.

I'll be getting 8/3 UF, only because of the length of the run and voltage drop.
Pretty heavy wire. I hope it'll fit onto your breakers and devices. How long is the run?
 
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Old 04-02-13, 04:13 PM
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I don't necessarily agree or disagree with Furd. I see it as basically a 240 volt circuit that is split into two 120 circuits at the shed. I don't know on further thought.

If you go with a multiwire circuit all you need is a disconnect. Cheapest way may be to use an unfused AC disconnect or you can install a box and 2-pole 20a switch (DPST).
 
  #22  
Old 04-02-13, 05:52 PM
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The better way to protect the two circuits is with two single-pole breakers with their handles connected with a handle tie.
Would you mind explaining why it's better that way?

Pretty heavy wire. I hope it'll fit onto your breakers and devices. How long is the run
I didn't think of that. The run is 110' outdoors, and another 60' indoors. I calculated a drop of 4.2V @ 20A, not including the length inside the shed to the actual outlets.

If you go with a multiwire circuit all you need is a disconnect. Cheapest way may be to use an unfused AC disconnect or you can install a box and 2-pole 20a switch (DPST).
That's easy enough. You're just talking something like this, right?
Leviton 20 Amp Commercial Double-Pole Toggle Switch
 
  #23  
Old 04-02-13, 06:24 PM
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I hope it'll fit onto your breakers and devices.
I just tried and was able to (barely) fit #6 stranded into a standard Murray 20A breaker, so unless the GFCI has a smaller terminal the #8 stranded will be OK. As for the shed side, the first place it will go is to the shutoff switch. For that, should I connect a short pigtail of #12 so that it fits the terminal properly?
 
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Old 04-02-13, 06:34 PM
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I dug out my 2002 NEC and read Article 300.5 and looked at the table. Then I looked up "voltage" under Article 100 (Definitions) where the term voltage is further broken down to Voltage of a circuit; Voltage, nominal and Voltage to Ground. Voltage of a circuit is defined as "The greatest root-mean-square (rms) (effective) difference of potential between any two conductors of the circuit concerned."

That along with Table 300.5 column 4 that states in part, "...120 volts or less with GFCI protection..." now tells me that a multi-wire branch circuit is NOT acceptable in any manner detailed in column 4. That leaves you to going back to 18 inch minimum depth or using one of the other methods listed in Table 300.5.
 
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Old 04-03-13, 06:33 PM
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Furd -

Thanks for diving in. If I start digging and it's "uneventful", maybe I'll change the plan, but given the # of rocks I hit while digging the footings for the shed itself I'm likely going with 120V/20A.

Thanks to all for the help!
 
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Old 04-03-13, 08:14 PM
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Honestly, if the digging is going to be that difficult I would dig down 8 inches, lay RMC and then cover it back up. Probably use one inch RMC to allow for any eventuality.
 
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