My first sub-panel


Old 08-29-05, 11:28 PM
Thread Starter
Join Date: Nov 2002
Location: Orange County, CA
Posts: 331
My first sub-panel

My 1968 house has AL wiring and I want to replace it with copper. Many reasons for this, most being peace of mind and I have some wires exposed now for a master bath remodel. More reasons if anyone wants them.

To make things easier I am thinking I will install a sub panel in the garage. The opposite side of the wall for sub is a bedroom closet.

Reason for the sub is that the main is at the far corner of the house and I am pretty sure it will be hard to run new wire to it. I will eventually upgrade the main from 100A to 200 and plan to buy one that is 40 circuits/40 spaces. I want the extra space just in case I need it later and 50 extra bucks is far worth it to me. The new sub will be 200A and 40/40 but in talking to the city building department, they issued me a permit but said they doubt the actual inspector will pass a 200A sub with a 100 main.

I still have to do a wiring diagram of all wires going everywhere but before I even start that, does the idea of putting in a subpanel to make the wiring easier sound reasonable? I have great attic access for the sub location but not for the main. I have read Cauldwell's Wiring a House, Wiring Simplified, parts of 2005 NEC, and this site for awhile.
Sponsored Links
Old 08-30-05, 05:00 AM
Join Date: Aug 2005
Location: Ohio
Posts: 63
Yes a sub panel is good for that application.

You need to upgrade your 100 amp panel at the same time tho. Your sub panel does not need a main breaker in it. The overcurrent protection will be in your main panel. I would install a 225 amp main and a 100 amp sub. Don't forget you have to keep the neutrals and grounds separate after the main panel. This means you will need a ground bar in the sub panel.

As for aluminum wiring, there is nothing wrong with it as long as it was installed correctly and you don't have moisture problems.
Old 08-30-05, 06:39 AM
Join Date: Sep 2000
Location: United States
Posts: 18,497
Make sure everybody is on the same page when you are talking about a "200A panel". Are we talking about a panel rated for up to 200 amps? Or are we talking about a panel feed from a 200-amp feeder breaker? There's a difference.

I see absolutely no reason not to use a panel rated for up to 200 amps as a subpanel if you want to. However, you probably want to feed it from a 100-amp breaker in the main. Discuss this with the inspector first to make sure you're okay. Tell the inspector that you have future plans to upgrade the main panel to 200 amps (I see no reason why you would need to do this at the same time), and that's why you're feeding a 100-amp sub from a 100-amp main. I don't see why he should have any trouble with that.

If you want to upgrade the sub to 200 later too, make sure you use wire rated for 200 amps between the panels.
Old 08-30-05, 08:46 AM
Join Date: Feb 2002
Location: port chester n y
Posts: 2,117
The basic Code issue is that the ampacity of the Feeeder Conductors are sufficient to supply the load of the circuits connected to the S-P. The "maximum" load on the Feeder is determined by calculations which in general are percentage-factors applied to the "total wattage" of certain specfic loads.What you DON"T do is to the calculate the load on the Feeder by simply adding the ratings of individual circuit-breakers.

As to the rating in amps of the S-P, the relevant Code Article is 408.30 which reads------" All panels shall have a rating NOT LESS than the minimum Feeder capacity----- calculated in accordance with Art. 220." The point is that the rating in amps of the S-P can exceed , but not be less than, the amapcity of the Feeder Conductors.

Good Luck and Learn & Enjoy from the Experience!!!!!!!!!!
Old 08-30-05, 10:23 PM
Thread Starter
Join Date: Nov 2002
Location: Orange County, CA
Posts: 331
Pulling armored cable

I appreciate everyone's answers. About the panel at 200A, what I mean is that eventually I want both panels to be rated for 200A to be safe, and yes, I plan to feed the sub with wire rated for 200 amps just to be safe. Which leads to the next question.

A while ago I spoke with one of the city inspectors and he said I should use armored cable to feed the sub. I am fine with that right now, but I have never installed armored although I am looking forward to do something new.

One of the biggest reasons for the sub is that the main is so hard to work on. The location is at a corner of the house where there is no attic access. I will somehow have to pull the armored cable from a spot in the attic to the main panel but I am not sure how.

I worry about this because a previous owner, who did a lot of good electrical work before me, ran a circuit from the main to the outside of the wall with conduit just below the panel and then into the dirt. It makes me think this person knew something I did not. Should I consider metal conduit from the attic through the cathedral ceiling space to the main panel? The conduit would not bend around the angle from the ceiling to the wall of course, but could keep the armored straight until it gets to the wall.
Old 08-31-05, 08:14 AM
Join Date: Feb 2002
Location: port chester n y
Posts: 2,117
If you insist on 200 amp Feeder Conductors to the S-P location, you can save much T & T by running 2 NM cables, each with an ampacity of 100, to two S-P's, each with a 100 amp rating.Bcuase of it's small-diameter and flexibility, NM cable is best suited for the stuctural difficulties you have mentioned. The "Main" panel will have to accomodate two 2-pole 100 amp C-B's.

For a Feeder with conductors with an ampacity of 200, you will need 3 #000 copper conductors + an EGC, depending on the type of Wiring Method, and terminating these conductors at the Main panel will be problematic, not to mention the obvious difficulties in routing the Wiring Method between the two connection-points.

Good Luck, and Learn & Enjoy from the Experience!!!!!!!!

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