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Thread: My Sub-Panel set-up and general electric questions... Good to go?

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    Question My Sub-Panel set-up and general electric questions... Good to go?

    I'm running 4 legs @ 125' long to the garage.( 10 guage THHM stranded southwire ) Two conductors ( hots ) One neutral and a ground.. I'm running them in grey PVC electricians pipe and putting them in a trench at 24" deep.. The 2 hots will be on a double pole 30 amp breaker which will run to a sub-panel in the garage.. The garage sub-panel will have one 20 amp breaker for 2 receptacles for well pump outlet and an outlet at work table for tools.. The other hot will provide for a 15 amp breaker for lighting, ceiling fan, and refrigerator outlet.. I want 220 / 30 amps out there in case I change over to something different down the road.. Plus, with the long run of 125' I need to suffice for voltage drop.. Please advise?

    Question 1) I have a boat load of 1/2 inch grey electrical PVC conduit stock. (I'd like to use it ) If I cant fit the 4 wires or if its way to tight will it be ok to run the ground outside the conduit in the trench?

    Question 2) Whats the deal with isolating the neutral from the ground on the sub-panel? ( NEC code )

    Question 3) Many plain receptacles and switches are rated for 15 amps, but its safe to use them on 20 amp circuits - why?

    Please advise and thank you for your expertise. You're helping me to save a few bucks and for that I am very grateful..

  2. #2
    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by Mike Pastorelli View Post
    I want 220 / 30 amps out there in case I change over to something different down the road.. Plus, with the long run of 125' I need to suffice for voltage drop.. Please advise?
    That is what I have, and I think #10 should be fine. However, I have solid wire running out to my workshop and I do not know whether stranded or solid might be better.

    Question 1) I have a boat load of 1/2 inch grey electrical PVC conduit stock. (I'd like to use it ) If I cant fit the 4 wires or if its way to tight will it be ok to run the ground outside the conduit in the trench?
    I believe you only need three wires since the garage will have its own ground wire and rod.

    Question 2) Whats the deal with isolating the neutral from the ground on the sub-panel? ( NEC code )
    I do not know, but that is why you do not need to run the fourth wire (as far as I know).

    Question 3) Many plain receptacles and switches are rated for 15 amps, but its safe to use them on 20 amp circuits - why?
    Because it is assumed each switch or receptacle in the circuit will not have more than a 15A load...and then the wire and breaker for the overall circuit are 20A since it is likely there will be more than one switch or receptacle being served on the circuit.
    Last edited by leejosepho; 05-26-2013 at 09:49 AM.
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    Electrical Contractor/Instructor jwelectric's Avatar
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    1/2 inch PVC and 4 #10 is good as long one is white from end to end and one is green from end to end

    The neutral can contact the equipment grounding conductor in the service panel only

    Yes more than one 15 amp receptacle can be used on a 20 amp circuit, a duplex is two receptacles

    Yes you will need four conductors and yes you will need to install a grounding electrode system at the remote building. If you choose rods for the electrode system you will need two

    In past codes you could install just the neutral but to be to today's code then four is required

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    DIY Senior Member bluebinky's Avatar
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    I'll attempt to explain why the neutral and ground are kept separate in the sub-panel. Hope this makes sense...
    - A heavily loaded neutral will have some drop and can have several volts (say 5 ~ 10V on a long run).
    - You want the grounds to be as close to zero volts (for safety) and not carrying any current.
    - If you ran a phone wire or metal gas or water pipe those could end up carrying some of the neutral current if everything was bonded together on both ends and the neutral and grounds are bonded in both panels.

    If I were going through the bother to trench 125' I'd lay 2 inch conduit in case someone wanted a welder, EV charger, or whatever in the future. Maybe put the small stuff in too for network or TV. Just me though...

    You probably know this, but no more the 360 degrees of bends total. Also, the receptacles (outlets) need to be GFCI protected.
    Last edited by bluebinky; 05-26-2013 at 12:57 PM.

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    DIY Senior Member Homeownerinburb's Avatar
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    The other posters have pretty well covered it. Follow JW's instructions on the grounding and bonding.

    A hint to make life just a bit easier as you pull your wire. Inject wire lube in all the conduit as you build it, such that you have lots of it.

    The wire will fly right down the conduit for your pull. Just be careful to not get dirt in the conduit as you build it.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by jwelectric View Post
    Yes you will need four conductors and yes you will need to install a grounding electrode system at the remote building. If you choose rods for the electrode system you will need two

    In past codes you could install just the neutral but to be to today's code then four is required
    I thank you for that correction, JW. I might have heard that before, and forgotten!
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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    Thanks again for all the informative replys..
    On the grounding, I'm going with a closed loop on those 2 rods and doubled up on the acorn @ 8' APART.
    Any ideas on the various types of lubricants for the wire pull and how do you propose I do this? I was thinking to fasten the wire to a telephone pole and slide the PVC down it as a helper holds the wire taut? I will be doing this in the street out front ( My ostriches and llama's have turned the back yard into a dirt fest ) Thanks

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    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by Mike Pastorelli View Post
    On the grounding, I'm going with a closed loop on those 2 rods and doubled up on the acorn @ 8' APART.
    No need. Unless you just like to over-do things.
    You also don't need two acorns on the first rod. You can just pass the wire through to the next.


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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by Mike Pastorelli View Post
    I was thinking to fasten the wire to a telephone pole and slide the PVC down it as a helper holds the wire taut? I will be doing this in the street out front...
    Be sure to get some pictures!
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

  10. #10

    Thumbs up

    Quote Originally Posted by leejosepho View Post
    Be sure to get some pictures!
    Yea, that sounded like I would be climbing a telephone pole to do that.. No, not the top of the pole, the base.... :-)

    Thanks for replys

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    DIY Senior Member Homeownerinburb's Avatar
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    Quote Originally Posted by Mike Pastorelli View Post
    Thanks again for all the informative replys..

    Any ideas on the various types of lubricants for the wire pull and how do you propose I do this?
    Wire lube (monkey snot) is readily available in home improvement centers and electrical supply houses. A quart will more than serve. It comes in a plastic bottle with a nozzle in the lid that fits into any conduit. Stick the nozzle in the conduit, squeeze. Look out, it will make getting a proper glue-up hard if you get it on the contact surfaces.

    Code does not allow you to gradually install wire into conduit and build up the conduit around the wire. One is expected to build the whole raceway and then pull the wire.

    Not that you would be the first if you did otherwise. And assuming that you neither have a long pull tape nor the desire to invest in one, you COULD use some strong string or twine, inserting it as you build the raceway. Just be careful not to glue it in a joint.

    30 amps at 240v is a LOT of power. Unless you intend to build a factory in the back yard, I don't think you will ever need more.

    It is a whacking big welder that needs more than that. I know a guy who is deathly serious about his welding rig. I put in 30 amps and he has no need for more.

    Remember: you are not running your table saw, your lathe, your welder, your chop saw, your air compressor, and your drill press all at the same time.

    I'm trying to think if you could get two lengths of #8 and two of #10 down half inch, and run a 40 amp service. Lord knows that 40 amps would handle your needs, refrigerator and all.

    Actually, that might be JUST over the legitimate capacity of 1/2" conduit. And while an inspector likely would allow you to downsize the ground wire, the neutral is another question. It surely would be a difficult pull in 1/2", 125', with two 90 degree sweeps. All the more reason to lubricate the conduit. And the wireman feeding the wire must be very careful that the wire not cross about, but go into the conduit all in the same order. 3/4" would have no problem with 4 lengths of 8ga.

    Don't forget: current code demands that wire smaller than #6 be color coded white for neutral and green for ground. Tape at both ends is no longer sufficient.

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