Outdoor shed wiring


  #1  
Old 06-02-06, 05:42 PM
Bob33
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Outdoor shed wiring

I'm putting in a pool. Will have a wood 10x14 shed near it for storage. A bunch of questions please:
1. Pool circuit will be run from a 60 amp GFI-protected subpanel in garage. Pump draws <20 amps. No plans for heater later.
2. Wiring to pool pump and thereafter to shed will be via THWN in grey PVC, 18" underground.
3. I want to run another circuit to the shed with THWN. For a 20 amp 120v circuit to the shed, I plan on 3 THWN: hot, neutral, and ground (12 or 10 gauge for an 85' run from sub to shed?)
4. In the shed, circuit will power lights and a couple of convenience outlets.
5. Plan on using PVC conduit in the shed with the THWN. Is this overkill; can I use UF?
6. Do I need weatherproof boxes inside shed?
7. Do I need a separate disconnect for the circuit for the shed at the shed? Or do I need a subpanel there with ground rod etc...?
An electrician will oversee/do this but the permit people are likely going to start their review and I'd like some advice from you folks.
TIA,
Bob
 
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Old 06-02-06, 06:25 PM
R
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1. The pool needs a 20 amp circuit. This must be individual wires in conduit with an insulated ground wire.

2. The pool must be a separate circuit from the shed.

3. I would run a multi wire circuit to the shed.

4. Your plan is fine. Where are you locating the convenience receptacle for the pool? In the shed won't qualify.

5. UF probably not (no protection). PVC okay.

6. Inside no. Outside yes. Must be GFCI protected.

7. You don;t need a sub panel, unless you want one. Yes, you need a disconnect. One or two switches.
 
  #3  
Old 06-03-06, 06:47 AM
Bob33
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Shed Wiring Follow-up

Thread below: http://forum.doityourself.com/showthread.php?t=266020

Ampacity/gauge calculator: http://www.powerstream.com/Wire_Size.htm
indicates that I need to uses 8 gauge wire for the '85 run for a 120v 20-amp circuit to the shed.
Question: Once at the shed, can I transition to 12 ga to make the connections and runs to the switches and outlets? If not, how do I make the connnections since 8 ga won't fit screw terminals on the devices?
TIA,
Bob
 
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Old 06-03-06, 06:56 AM
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Yes you can reduce the wire size after reaching the shed. Do not reduce it below #12 (because of the 20 amp breaker).
 
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Old 06-03-06, 07:07 AM
Bob33
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Thanks Nap!
 
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Old 06-03-06, 07:22 AM
R
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Bob,

Please keep all related posts in the same thread. It makes it much easier on everyone involved.

In my opinion, using 8-2 for this run is a bad idea. You will have twice as much power using 10-3, and still be okay as far as voltage drop is concerned.

The calculation you performed assumes 20 amps at 120 volts. If you really think you will approach 20 amps, especially with multiple loads, then you definitely want to run a multi wire circuit.
 
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Old 06-03-06, 07:48 AM
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Originally Posted by racraft
The calculation you performed assumes 20 amps at 120 volts. If you really think you will approach 20 amps, especially with multiple loads, then you definitely want to run a multi wire circuit.
How do you calculate voltage drop, racraft. When feeding an undesignated circuit, what are you using for voltage drop calc parameters. Since the circuit can ultimately be loaded to 20 amps, how do you justify calculating using less.

(yes I know #10 at 16 amps does come out fine for voltage drop)

It's not that I disagree with your advice of the multiwire circuit, just want to understand your justifications on the calcs.
 
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Old 06-03-06, 08:05 AM
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I agree that one would need 8 gage wire if all 20 amps were pulled at 120 volts, to stay within a reasonable voltage drop.

I am questioning the use of 20 amps. Rarely does a 20 amp circuit get loaded to 20 amps. At a lower amperage a reasonable voltage drop can be maintained using 10 gage wire(or even 12 gage wire if the current is low enough).

I am suggesting a multi wire circuit to help with voltage drop and to provide more power to the shed. With lights on one half of the circuit and by splitting other loads, the voltage drop can be cut up to 50 percent.

I also hear time and time again about how people wish they had planned for the future when they ran that circuit.

Some people recommend doubling your estimate of what you need. To me that's overkill in some instances (like with a service upgrade). Bob thinks he needs a 20 amp circuit, I am suggesting to double it.

One reason to put in the multi wire now it is that if he wants to do so in the future, the existing circuit needs to be eliminated, causing a waste of the wire (unless in conduit where the extra wire can be added). Further, using 10-3 or even 8-3 means that a small sub panel could be installed at a later date.
 
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Old 06-03-06, 08:17 AM
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Thanks.
Like I posted, I don't disagree with you at all on extra now rather than "I wish" in the future. This amount of extra really is warranted and advisable. The little calculator I use said #12 would be ok up to 10 amps and #10 up to 17 amps. (without temp consideration)

I just deal with a lot of theoreticals in my work. I have to consider worse case scenarios like women in an office and how many of those darned electric heaters are going to get placed under desks and things like that when designing circuits and loads.
 
  #10  
Old 06-03-06, 09:45 AM
Bob33
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The shed will really be more storage than anything; the only elec load might be a dorm fridge for beverages during the summer. So, in reality, it will likely never get near the 20 amps. The concern I have in using 10 or 12 ga, is the electrical underwriter will likely fail the install since the rated capacity of the wire is exceeded for this distance for the 20 amp breaker installed.
I am going to use sched 40 PVC conduit so if I do see the need, I can always pull more.
What size conduit for sched 40 PVC with 3 8 gauge wires?
Thanks,
Bob
 
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Old 06-03-06, 09:55 AM
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No, the capacity of the wire will not be exceeded if you went with 10 or 12 gage wire. 10 gage wire is rated for 30 amps and 12 gage wire is rated for 20 amps. The distance is immaterial to the current. The circuit breaker will protect the wire.
 
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Old 06-03-06, 10:13 AM
Bob33
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Originally Posted by racraft
No, the capacity of the wire will not be exceeded if you went with 10 or 12 gage wire. 10 gage wire is rated for 30 amps and 12 gage wire is rated for 20 amps. The distance is immaterial to the current. The circuit breaker will protect the wire.
I know the NEC mandates 12 ga for 20amps but I thought the NEC also wants to maintain less than a 2% voltage drop across the distance covered by circuit wiring. Using 12 ga for the '85 feet will give me a 4.6% drop. I'm not sure what that does to a fridge compressor but might this lower than rated voltage negatively affect some other devices?
Bob
 
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Old 06-03-06, 01:22 PM
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The NEC is concerned with safety. They don't really care what damage you do to your equipment. Lights will be dimmer with a voltage drop. Mortors will be damaged if the drop is too much.
 
 

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