Adding a subpanel to subpanel

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Old 05-26-20, 05:15 PM
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Adding a subpanel to subpanel

While I have done some basic wiring in a main panel, this is new to me & based on what I was told, I'm a bit confused & honestly a little afraid I've been mis-lead. I'm almost afraid to ask for fear, I've made a mistake.

I have an existing sub that is wired from the main. It has 4 wires: 2 black hots, a white neutral & a bare ground.

I am installing a new sub in a new storage shed which will be totally 120v. There will NOT be any 240v lines in this shed.

When I bought supplies at an electrical supply warehouse/retail company (Stuart Irby), the guy gave me #6 (I think), 3 wire bundle that is all wrapped together.... 2 black hots & a black with a white stripe neutral. I was expecting 4 wires like in the existing sub.

I am going to use a 40 amp double pole breaker (since I've never seen a single pole 40 amp breaker) to run out to the shed. Wont I need 4 wires for this? Two hots from the breaker, one neutral & one ground & run that to the new sub in the shop? I know that will give me 240v, but I don't need 240v.... only 120v, but I need 40 amps going to the sub.

I guess my question is mainly about the correct breaker & how to wire this from sub to sub with only 3 wires.
 
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Old 05-26-20, 05:44 PM
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Sounds to me you have the wrong wire for your use. Does it have an overall jacket and what are the markings on the wire?
 
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Old 05-26-20, 05:44 PM
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When you install a 120 volt only subpanel you need 3 conductors for ground, neutral, and one hot.

You feed it usng a single breaker in the supra panel.
i
 
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Old 05-26-20, 06:15 PM
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You say you don't need 240v to the shed but you say you need 40 amps. IF you were to use 4 wires at 20 amp you would in essence have the 40 amps you need. That is unless you actually have a 40 amp 120v load you need to feed.

They do make single pole 40 amp breakers for most panels but they are rarely used. If you use the wire you bought you would use one wire as the hot (black) one wire as the neutral (white stripe) and one wire for the ground (other black remarked as green) Just remember you will only energize half of the subpanel unless you somehow made a splice to the wire (I assume #8) which will be very messy.

If I were you I would use the wire you bought (since you can't return it anyway) but add a separate ground wire (#10 green). I know you say you do not need 240 volts to the shed but you don't have to use it. Just wire all your loads and balance it on the two legs going to the shed. All 120v.
 
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Old 05-26-20, 06:34 PM
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If the wire is a jacketed cable it's a NEC violation to add a separate ground conductor being a new installation. All conductors are to be in the jacket. If the cable is a non-jacketed assembly of conductors, #6 is not allowed to be re-identified, a green ground can be added. This is why the OP needs to identify what cable he has. I'm having a sneaky feeling the wire is URD which is for outside use only.
 
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Old 05-26-20, 06:48 PM
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Sounds to me you have the wrong wire for your use. Does it have an overall jacket and what are the markings on the wire?
Yep, I think so too. That's what I was afraid of. I would have thought the guy at the electrical supply co would have been sharper than I on this stuff but either he aint or he misunderstood & I don't see how there could have been a misunderstanding. He knew exactly what I'm doing here.


When you install a 120 volt only subpanel you need 3 conductors for ground, neutral, and one hot.

You feed it using a single breaker in the supra panel.

So, you're saying I need to use a single pole 40 amp breaker in both subs. One to feed from the existing panel & one to feed to the new sub?
This was my thoughts but, I didn't know single pole 40 breakers existed.


You say you don't need 240v to the shed but you say you need 40 amps. IF you were to use 4 wires at 20 amp you would in essence have the 40 amps you need. That is unless you actually have a 40 amp 120v load you need to feed.

I'm going to have one 8000 btu heat/air window unit running year around & at least 3 freezers & one
refrigerator minimum. Plus 3 LED lights & two ceiling fans. I'll also have a few more outlets in case I need to plug in anything else in the future. I need to be sure I have enough to run all that without over loading a breaker. 40 amps should be adequate to run all that in case a couple of things kick on at the same time along with the AC.
No single item will have a 40 draw in itself.

If I were you I would use the wire you bought (since you can't return it anyway) but add a separate ground wire (#10 green). I know you say you do not need 240 volts to the shed but you don't have to use it. Just wire all your loads and balance it on the two legs going to the shed. All 120v.
This was my thought on how to correct it if I kept the current setup.
 
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Old 05-26-20, 06:56 PM
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You need to provide detailed info on the wire you have to get correct info for what you can do.
 
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Old 05-26-20, 07:23 PM
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If the wire is a jacketed cable it's a NEC violation to add a separate ground conductor being a new installation. All conductors are to be in the jacket.
250.134(B)

If the cable is a non-jacketed assembly of conductors, #6 is not allowed to be re-identified, a green ground can be added.
A jacket or no jacket IMO it would still be considered a cable.
 
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Old 05-27-20, 05:09 AM
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There is no jacket enclosing all three wires. This is just three individual wires that are kinda twisted together.

I am just beside myself that I didn't question the man more than I did, but throughout this project, the man has really been a big help & has always been spot on giving me the correct stuff. I guess he just misunderstood what I was asking for in this specific part of the project.

The wire is: Southwire C (UL) AWG2 Type USE-2 60 MILS XLP INSULATION 60
 
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Old 05-27-20, 06:17 AM
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The subpanel may or may not have a top breaker. If not then you need a master switch (40 amp 120 volt single pole) at the shed.

I don't know how well y ou could do this but with 3 unjacketed conducors "kinda" twisted together it would seem simple to buy a fourth conductor, green in color, and "kinda" twist it together with the other three. This last wire would have to be a little longer since when twisting it it will not go as far compared to stretched out straight. It would also need to be direct burial rated if you are going to bury it. Ten gauge for the ground would go with a 40 amp 120 volt or 120/240 volt feed.

Starting with two blacks and one white striped black, the combinations and permutations of what things you may or may not do and what things an inspector may or may not pass are too numerous for me to second guess and make recommendations on.


If you were able to pull off the preceding paragraph and at a later date you found you needed more power then it would be a small step to convert to 120/240 and not have to redo the feed from the house to the shed.
 
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Old 05-27-20, 06:20 AM
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The wire you have is URD and is USE-2 rated only which means it has to be terminated outside of the structure because it's not fire resistant insulation. You will need to use junction boxes and transition to different wire for entry into the house and into the shed. This is provided the panels are inside the structures. If the panels are outside panels then you have no problem. The wire you needed is Triplex 600V Secondary UD RHH or RHW-2 or USE-2 which is also direct bury and fire resistant and can go inside. These direct bury unsheathed/unjacketed cables will need to be in conduit where above ground and inside the structure. If you are having this work inspected you need to check with your local inspector to see how they will allow the wire you have to be used. If you aren't having inspections then the best you can do is tape the ends of the one wire with the stripe white for neutral and another wire ends green for ground. This will provide you with 120V as earlier said. If using conduit underground the cover needs to be 18", if direct bury it needs to be 24".
I'm sorry you have this aggravation. I see too many times that DIY'ers are sold the wrong wire even at supply house where you'd think the sales people would know better.

Edit: You can add the green #10 Cu or #8 Al for the equipment ground and have 240V. If the subpanel at the shed is a main lug panel and has 6 or less breakers a main disconnect is not need at the shed.
 

Last edited by pattenp; 05-27-20 at 06:48 AM.
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Old 05-27-20, 06:57 AM
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So, let me see if I am on the same page with Allan.
If I put a 40 amp single pole breaker in the existing sub & the same in the sub in the shed as the main breaker to feed the box, I can use the 3 wire set that I have by using it as one hot, one neutral & one ground. This was my initial reason for wanting a single pole breaker after getting the wire I got. In my limited knowledge this should work safely & correctly... correct?

But, in the end, should I do it that way in my scenario? Or should I just buy two double pole breakers (one for each sub) & add a ground to my current 3 wires?

Just for additional info, I have already run this 3 wire bunch in 1-1/4" conduit which is now buried. I have one elbow in the run about 18" - 24" from the end of the conduit. The run is about 100 ft total. Is there going to be enough room to reasonably pull a 4th (ground) wire through the conduit? I don't really have any correct equipment to pull the wire with. I'll just use my JD lawn tractor to pull it with. If that wont pull it, I'll use my Kubota utility tractor. (FYI, I put the wire in the current buried conduit, one joint at a time.)

And for Patten....... this project wont be inspected.
 
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Old 05-27-20, 07:36 AM
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It's going to be a pain getting that ground pulled with the other wire already installed. You'd need to put a pull rope on the existing cable and pull the cable back out and attach the ground and pull the bundle back in using the pull rope. If you don't really need 240V then stick with 120V using the three wires as you understand is correct. You can use a double pole breaker in the shed and jumper the hot to both lugs of the double pole breaker to have both panel legs hot ( but will not have 240V). If you have a Square-D panel some of their breakers can be double tapped under one lug. Otherwise you will need to pigtail the one hot wire to the lugs of the double pole breaker. Since you are back feeding a breaker for the input feed you need to get a tiedown screw/clamp the fasten the double pole breaker in place.
 
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Old 05-27-20, 08:01 AM
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Ok, through all of this (although it was educational & helped me understand my issue & to know I was correct), the man from Irby just called to let me know my new sub came in & I told him what has happened. He told me to just bring the wire back & he'd replace it with a 4 wire run. I told him I had already run it & he didn't give me any grief, & said just bring it back & he'd make it right.
So, I'll have all the right stuff, the way I know how to do it. Four wires with double pole breakers.


I appreciate everyone's educational info. Very much appreciated!
 
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Old 05-27-20, 08:56 AM
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Just make sure the wire is just not only rated USE-2. If you see this before going to pick it up and if the wire will be in conduit panel to panel you can use XHHW-2 Al, it is not direct bury but can be in conduit underground and also run inside of house and shed in conduit.
 
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Old 05-27-20, 09:00 AM
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ok thanks patten..................
 
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Old 05-28-20, 09:40 AM
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Note: Just an update in case there are further discussions down the road everyone will be on the same page.

The company decided that instead of returning the wire, they would give/sell me a run of #6 ground wire for this project so I would .... in the end, have four wires. Two hots, one neutral & a ground. I am ok with this.

Since I only have one elbow, about 18" from one end, I am going to try to pull this #6 without removing the existing 3 wires already in the 1-1/4" conduit. If it cant, I'll remove the 3 wires & pull them all at once. I think it'll be easier if I pull from the long end toward the elbow.
 
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