Ground wire or no ground wire for sub panel

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Old 01-31-17, 02:10 PM
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Ground wire or no ground wire for sub panel

Hi guys newbie here.
i'm installing a 120v sub panel at my shop which requires approx. 110f of wiring. I will be installing a ground rod at my shop.
here's my question:
Do i need to pull a ground from my source panel since i'm installing a ground rod at the sub panel? the reason for question is i'm a little tight on pvc conduit ID.

thanks
John
 
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Old 01-31-17, 02:19 PM
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Ground rod is GEC (Ground Electrode) conductor for atmospheric charges. The ground from your panel Is the EGC (Equipment Grounding Conductor). It provides a low resistance path to clear faults such as hot shorting to the metal cases of equipment. You need both.

You won't find a readily available panel for 120 volts. How do you plan to convert a 240 volt panel to 120 volts?
i'm a little tight on pvc conduit ID
Then you used the wrong size. What size wire are you using?

It sounds like you were unfamiliar with how to do this. Tell us what you need to power at the shop. If you need no more than two 20 amp 120v circuits a multiwire circuit with no subpanel would be enough. If you need more normally a 120/240 sub panel is a better choice.
 
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Old 01-31-17, 02:30 PM
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Is this a detached shop or attached to a home?
 
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Old 01-31-17, 02:49 PM
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it is detached. im using #4 in a one inch pvc. when i said it would be tight, i wAS thinking about only me having to do the setup with wounded wires and pulling it myself. Could'nt i just install a small junction box and connnect hot to bus, neutral to the neutral bus and gnd to gnd bus? I need 40amps at shop. nothing in shop will pull over 15 amps starting
 
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Old 01-31-17, 03:51 PM
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it is detached. im using #4 in a one inch pvc.
That is just wrong. I hope you can return it.
I need 40amps at shop. nothing in shop will pull over 15 amps starting
Then at most you need two #8 black, one #8 white, and One #10 green. 1" PVC conduit is good for nine #8 so you should have no problem pulling it. You will need a 40 amp breaker at the main panel. At the shop a 100 amp main breaker panel would be a good choice. It provides room for plenty of breakers, the main breaker provides the disconnect needed if you have more than six breakers, and they are usually the cheapest choice if you get a main breaker kit. (Main breaker kit includes the main breaker several of the most common sizes of branch circuit breakers.) You will have t probably buy and install a ground bar.

Actually from what you have describe you could probably use #10 on a 30 amp breaker. But going to #8 gives you some extra head room.

(Just a side note: About the largest commonly found 120 volt breaker is 30 amps. Your # 4 is goof for 70 amps or more. No way you could have used it to capacity for a 120 volt subpanel.)
 
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Old 01-31-17, 05:08 PM
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#4

My voltage drop calculator gave me a 2.29%drop with 40 amp load, 120v, at 110 ft. Trust me, I did not want to buy 240ft of #4. Thank you for your insight. Can't I just pull what I have (2/#4-(one for hot and one neutral and a ground)) from a 50 amp breaker.
Land the hot on one lug of panel and just make sure that the circuit breakers land one that bus?
 
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Old 01-31-17, 05:14 PM
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Four #4 THHN/THWN will fit in 1" PVC conduit. What is the type of #4 that you have?
 
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Old 01-31-17, 05:26 PM
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You will only need #10 for ground.
My voltage drop calculator gave me a 2.29%drop with 40 amp load, 120v, at 110 ft.
That is why you run 120/240v not 120v. What you are doing is not best practice but if you want to do it it will work.

Edit: +1 for Pat's answer below. That would make the most sense.
 
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Old 01-31-17, 05:26 PM
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Can't I just pull what I have (2/#4-(one for hot and one neutral and a ground)) from a 50 amp breaker.
Land the hot on one lug of panel and just make sure that the circuit breakers land one that bus?
Yes you can. But why not just buy a piece of #8 for the EGC and you'll have 120/240. That is if you have room in the main panel for a double pole breaker instead of the single pole.

Edit: Excuse me. I wasn't catching you only have enough #4 for two wires. I was thinking you had three. Brain freeze
 
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Old 01-31-17, 05:30 PM
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You will only need #10 for ground.
Because the #4's are oversized and good up to 85A (if THHN or equivalent) the ground will need to be at least a #8. I assume the #4 are copper.
 
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Old 01-31-17, 05:36 PM
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Remember if you don't use a main breaker panel you will need a disconnect if you have more than six breakers.
 
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Old 01-31-17, 05:39 PM
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Got me Pat. Wasn't looking at it as oversized. I should have. I deleted my comment.
 
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Old 01-31-17, 05:42 PM
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Thanks for all your input does!. The number four is THHN. And could you explain about buying the number eight and making it a 240? I guess I didn't catch that in the thread because I'm using my mobile phone so it's very possible I missed it
 
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Old 01-31-17, 06:36 PM
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The #8 is for the ground. I was thinking you had enough wire for three #4's and with adding a #8 would give you four wires for 120/240. Being that you only have enough wire for two #4's and adding a #8 for the ground will only give you 120V. You can jumper the two sides of the panel bus to use both sides as 120V only with no 240V. But don't put two ends of wires in one bus lug to jumper to the other lug. Use a Polaris connector and two pigtails to the bus lugs.
 
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Old 01-31-17, 06:45 PM
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The #8 copper is for the ground wire.

Perhaps rather then trying to tell you how to wire it, you should tell us what you have bought and installed at this point that you can't take back to the store. All of this could have been much simpler if you started asking questions before starting.
 
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Old 01-31-17, 07:20 PM
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If the #4 was up sized the ground will also need to be up sized by the same percentage. It would not longer be based on the breaker size.
 
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Old 02-02-17, 10:23 AM
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sorry for the novel you are about to read

OK guys here's the stats. I have a sub panel that the pool company put in for my pool equipment this sub panel is fed from a 60 amp breaker in my main service panel with number six wire. It is about 10 feet at the most and this is the length of wire from main service panel to outside existing pool equipment subpanel . This existing subpanel is where I plan to grab my power from and go 110 feet to my shop. Now I will have no need for 240V in my shop however after talking to you guys I'm going to make a 240V panel because I came across an entire roll of number eight at my dads house, who has since passed away and so instead of buying any electrical equipment, I'm Pilfering his stock, plus I've been laid off for six months now and my unemployment benefits ended this month. However in my initial assessment, my calculations indicated that I needed a #4 wire to achieve this so I spent $230 and purchase this cable. Now, I can still run this cable and jumper the lugs and make it a120V panel however I would prefer, since I now have the number eight is to go ahead and pull 4 wires. I don't have a number 10 for the ground I have a number 12 but the easiest way to do it is to just pull 4 number eights and here's my plan. Is to put line 1 and line 2 from the lugs of the existing subpanel were the number sixes are landed and then go to the shop and install a small breaker panel. My existing pool equipment subpanel does not have a main breaker in it, on a sidenote whenever I plan on using the shop I intend on shutting the pool equipment off so if I'm using #8 wire am I going to need a main breaker at my new subpanel at the shop? Or can I use the 60 amp breaker located at the service panel that is providing power to the existing pool equipment subpanel. And if you guys can understand all of that then you were geniuses.LOL . But the good thing is I do have space in the existing pool equipment subpanel and I also have an unlimited amount of number eight. Also if anybody is in the market for two lengths of number four, 120 feet per length for a total of 240 feet of number four wire THHN
 
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Old 02-02-17, 11:45 AM
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Is to put line 1 and line 2 from the lugs of the existing subpanel were the number sixes are landed and then go to the shop
Even if you were allowed to put two wires under one lug (usually you aren't) you can't. The wires need to go to a breaker in the supplying panel.
am I going to need a main breaker at my new subpanel at the shop?
No, but if you have six or more breakers you need a disconnect and the main breaker will serve as your disconnect. Since main breaker kits are often as cheap as main lug panels and even cheaper when you add in the included branch circuit breakers in the main breaker kit a main breaker kit is the cheapest solution usually. I'd suggest a twelve space 100 amp main breaker panel.
I came across an entire roll of number eight at my dads house,
You need black, white, and green #8. By strict code wires smaller than #4 can't be remarked but sometimes an inspector will allow it. Ask first.

Site doesn't allow advertising and for the record if it is really THHN you couldn't have used it in buried conduit. I suspect though it is dual rated THHN/THWN.
 
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Old 02-02-17, 08:06 PM
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Actually, if the panel will accept more than 6 breakers/circuit you must have a disconnect.
 
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Old 02-02-17, 08:43 PM
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Others see this as unnecessary until more than 6 are installed. Depends on the inspectors interpretation. I am in the more than 6 camp, not based on future changes.
 
 

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