Shared neutral supplying subpanel

[lowatter]

Newbie to this forum here. I have a question that I need to resolve fairly soon. I have 10/3 from a dual pole 30A breaker using one side of the breaker from the main panel that is direct burial wire going to a junction box outside the house. I need to supply a sub panel to a building. Can I use (2) separate 10/2 UFB wires tied into the junction box and share the neutral and ground wires and use both sides of the 30A double pole breaker? I've read that there may be magnetic field concerns on the neutral. The subpanel has only single pole 15 and 20A breakers on it.
If possible it would save me money and time as there is currently a 10/2 UFB supplying the subpanel with a jumper to make it a 120V panel. Please respond asap as I need to make a decision and get materials etc. Thanks!

 

[Megawatt]

Newbie to this forum here. I have a question that I need to resolve fairly soon. I have 10/3 from a dual pole 30A breaker using one side of the breaker from the main panel that is direct burial wire going to a junction box outside the house. I need to supply a sub panel to a building. Can I use (2) separate 10/2 UFB wires tied into the junction box and share the neutral and ground wires and use both sides of the 30A double pole breaker? I've read that there may be magnetic field concerns on the neutral. The subpanel has only single pole 15 and 20A breakers on it.
If possible it would save me money and time as there is currently a 10/2 UFB supplying the subpanel with a jumper to make it a 120V panel. Please respond asap as I need to make a decision and get materials etc. Thanks!

No you can never share neutrals. What amperage of sub panel are you wanting to add ? Help me help you.

 

[lowatter]

I should've mentioned that it's for the same subpanel. It's a 70A subpanel with (3) 20A and (3) 15A homeline breakers.The panel is wired with a jumper combining legs that I want to separate so only 3 breakers are on each leg. What confuses me is if a straight run of 10/3 on a 30A dual breaker from the main panel to the sub feeds both legs on the sub panel, why couldn't you have (2) 10/2 wires one black on each leg meet in a junction box tied to the 10/3?

 

[Megawatt]

I should've mentioned that it's for the same subpanel. It's a 70A subpanel with (3) 20A and (3) 15A homeline breakers.The panel is wired with a jumper combining legs that I want to separate so only 3 breakers are on each leg. What confuses me is if a straight run of 10/3 on a 30A dual breaker from the main panel to the sub feeds both legs on the sub panel, why couldn't you have (2) 10/2 wires one black on each leg meet in a junction box tied to the 10/3?

I’m a little bit confused but are you wanting to parallel two 10/3 coming off of 30 amp double pole breakers from your main panel. Are you thinking if you do what it sounds like. By code you can’t parallel nothing smaller than 1/0 wire. I guess your saying that right now you have one 30 double pole breaker feeding your panel and you want to add another 10/3 branch circuit. My suggestion is to add 3 # 6 wires being your 2 hots and neutral plus a # 10 ground wire. Install a 60 amp breaker for the new wires in your main panel. I’m just a little confused. The proper way to do is what I told you

 

[lowatter]

The SUB panel is incorrectly wired with a jumper combining legs(it's wired as a 120V only panel) that I want to separate so only 3 breakers are on each leg. What confuses me is if a(prefered) straight run of 10/3 on a 30A dual breaker from the main panel to the sub feeds both legs on the sub panel, why couldn't you have (2) 10/2 wires one black on each leg meet in a junction box tied to the 10/3 and then to the 30A double pole breaker?

 

[lowatter]

FWIW...I decided to just do a straight 10/3 run off the 30A double pole breaker(from the main panel) to the sub panel(which is grounded to a grounding rod) with 160' feet of 10/3UFB to eliminate any neutral/ground issues. It's a LOT of extra trenching/work however.
I guess my next question would be, with such a long run are there excessive heat issues because of the long run? Thanks for your input.

 

[Megawatt]

FWIW...I decided to just do a straight 10/3 run off the 30A double pole breaker(from the main panel) to the sub panel(which is grounded to a grounding rod) with 160' feet of 10/3UFB to eliminate any neutral/ground issues. It's a LOT of extra trenching/work however.
I guess my next question would be, with such a long run are there excessive heat issues because of the long run? Thanks for your input.

You shouldn’t have no problem with the distance and if it is a sub panel and you have a full 240ac feeding it. Since you have pulled another 10/3 to achieved your 240vac panel with 2 hots, 1 neutral and 1 ground wire then a ground rod is not required. Good luck with your project.

 

[lowatter]

Thanks again. I do have one more question that would save me a lot of time and some money. Is it ok to keep the existing (3) wire-nutted junction boxes that are running that have 10/3 in them or is it imperative to make a straight uninterrupted run to the subpanel? One is near the main panel and the other (2) are at 20 and 50 feet from the panel out in the yard with weather tight J boxes.

 

[Megawatt]

Thanks again. I do have one more question that would save me a lot of time and some money. Is it ok to keep the existing (3) wire-nutted junction boxes that are running that have 10/3 in them or is it imperative to make a straight uninterrupted run to the subpanel? One is near the main panel and the other (2) are at 20 and 50 feet from the panel out in the yard with weather tight J boxes.

Splices like you stated is fine as long as it’s in a weather proof J box which is what you stated also. Good job

 

[lowatter]

Thanks Megawatt. I appreciate you taking the time to address my concerns. I'll feel more confident tomorrow when I wire everything up.

 

[davesparks]

Thanks again. I do have one more question that would save me a lot of time and some money. Is it ok to keep the existing (3) wire-nutted junction boxes that are running that have 10/3 in them or is it imperative to make a straight uninterrupted run to the subpanel? One is near the main panel and the other (2) are at 20 and 50 feet from the panel out in the yard with weather tight J boxes.

As a general rule in electrical work wherever possible a straight, uninterrupted run of cable is preferable to one with joints in it.