Adding sub-panel for basement wiring


Old 06-07-06, 11:06 AM
Thread Starter
Join Date: Jun 2006
Posts: 4
Adding sub-panel for basement wiring

I need to add a 50-amp sub-panel to my 100-amp main panel to power my newly remodelled basement. I am adding a sub-panel to make my life easier because my main panel is a wiring mess from previous owners. I was told by the electrical inspector that I need to run 3-conductor cable and isolate the grounds of the two panels. However, I cannot find anything in any of my home-improvement and electrical books that explains the wiring diagram necessary.

I have 3-conductor #6 cable and need to know how to wire the sub-panel. My sub-panel does not have a breaker of it's own, only three screw terminals for heavy gauge wire. My sub-panel is located 5 feet from the main panel and is completely isolated (no metal connections).

Here are my assumptions:
1. Connect the new 50-amp breaker in the main panel to the red and black wires of the #6 cable. Connect these wires to the two hot terminals in the sub-panel.
2. Connect the white wire of the cable to the neutral bar of the main panel. Connect the other end to the neutral bar of the sub-panel.
3. Connect the bare copper wire of the cable to the frame ground of the main panel. Connect the other end to the ground bar in the sub-panel.

Sponsored Links
Old 06-07-06, 11:26 AM
Join Date: Apr 2006
Location: USA
Posts: 133
" I was told by the electrical inspector that I need to run 3-conductor cable and isolate the grounds of the two panels".

You need a 4 conductor cable. The neutral and ground conductor are to be isolated in your new panel.

"I have 3-conductor #6 cable and need to know how to wire the sub-panel."

You can not isolate the neutral and ground with a 3 conductor cable.
Old 06-07-06, 11:43 AM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
If your main panel really is a mess, then a better solution to your problem would be a larger main panel.

You almost have it correct. But let's address your terminology first. It's not three conductor cable. It's FOUR conductor cable. You need three current carrying conductors and one ground wire. It sounds like you know the correct wire, just are using the wrong term. This will only confuse people reading this, and perhaps yourself as well..

At the main panel the ground buss and the neutral buss are usually the same thing. This will be evident by the fact that grounds and neutrals from your house circuits connect to the same place.

In the main panel the ground and neutral feeding the sub panel connect to the ground buss and neutral buss. In the sub panel these MUST remain separate. This usually means buying and adding a ground buss, as most panels only come with one bus. Make sure that the ground buss in the sub panel connects to the panel itself and that the neutral buss does not.

Personally, instead of a 50 amp cub panel, I would use a 100 amp panel that has main breaker. This will be better for you in the long run.

Finally, this is not a good first or second job for a do it yourselfer. Before you do this yourself, seriously consider whether you want to assume the risk that goes along with this. Doing this wrong could burn your house down, or worse yet, kill you or someone else.

Better safe than sorry.
Old 06-07-06, 04:48 PM
Thread Starter
Join Date: Jun 2006
Posts: 4
I did purchase the correct cable and was using incorrect terminology as you indicated. I did purchase the ground bus for my new panel as you instructed but was a bit confused when I noticed the ground bus and neutral bus in my existing main panel were connected. This caused me a bit of confusion as I wondered why they had to be isolated in the subpanel but not in the main panel. But building codes are there to follow, not necessarily to understand.

I do have a local permit to do this work and will get everything inspected closely by the town inspector before turning on the power to anything. I'm not the kind of person that tries to get something past the inspector, I'm the kind of person that wants to make sure it's done right. I have a vested interest in doing this project right and honestly feel safer knowing I'm doing it.

Why do you make the recommendation about the panel? I only ask this as I no longer have the box to return the panel I bought. If this is just personal preference then I'm stuck with my inexperienced decision. If this is a safety concern then I'll eat the cost of this panel and purchase a new one.

Thank you for your clarification.
Old 06-07-06, 04:56 PM
Join Date: Mar 2006
Location: Great Barrington MA
Posts: 532
you must live somewhere where they have sane permit laws. If you are getting it inspected before use I would say your fine. A 50A sub will be more then enough to run a basement I don't care what anyone says. In fact I live in one of my basements and have it powered by a reverse fed 50A breaker which is about the same thing as a main. 2 years and no problems here or at anyother of my jobs
Old 06-07-06, 05:57 PM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Let me first try to explain the ground issue. The ground wire is for safety. Under normal use the ground carries no current. The ground is connected to the neutral at one place and one place only. If you were to connect the ground and neutral together in your sub panel, then the ground would no longer carry no current, but instead would carry about the same amount of current as the neutral (assuming the same size wires). You isolate the ground and neutral at the sub panel to keep current off the ground.

My recommendation on the panel was because a panel with a main breaker is much easier to understand and wire than a panel without a main. In some ways it is safer too. I also suggested a larger panel in case you need to add additional loads later on. With your current sub panel, you are limited to 50 amps. With a larger sub panel you could increase the wire size and make it an 80 amp sub panel or even a 100 amp sub panel.
Old 06-07-06, 06:11 PM
Join Date: Mar 2006
Location: Great Barrington MA
Posts: 532
I might have agreed with you that it was a bad idea for a DIY project but he seems to have a basic understanding and even more importantly he's getting it inspected. Any inspector worth his salt is going to scrutinize something like that pretty thoroughly so all in all should be ok. that's why I get angry sometimes at laws that allow any homeower to conceal utilities uninspected. More is better I suppose but I still think that 50A is more then sufficent for an average basement and even a few circuits free for future add ons. Most of the basements I did there was room in the existing panel for the 3-4 circuits I needed to add but if I added a sub it was a reverse feed 50A
Old 06-07-06, 06:22 PM
Banned. Rule And/Or Policy Violation
Join Date: Feb 2006
Location: North of Boston, MA.
Posts: 2,113
Racraft is correct in all above. However, I feel with the distance between the 2 panels, that the main lug feed is fine. Logic being the close proximity (5') this should not be an issue.
If the new sub panel came with a green bonding screw...Discard it.

While your at it, If you are comfortable with this work, In the daylight, Shut down your main breaker and clean up the main panel. Good luck.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes