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-   -   Wiring 100A subpanel (http://www.diychatroom.com/f18/wiring-100a-subpanel-11068/)

nebulous 08-28-2007 11:16 AM

Wiring 100A subpanel
 
After reviewing comp1911's recent post as well as several others on the net I have a couple of questions regarding my install of a 100A subpanel off of my tragically small 200A main panel.

I am planning to move the dryer over to the subpanel and use its slot in the main panel to feed the subpanel thru a 100A breaker. It appears that to avoid controversy and be safe I'll need to use #2 copper hots and neutral and a #4 copper ground wire from the main to the sub.

First question: Where can I get the wire? The largest wire my local Home Depot carries is 2224 aluminum. When I asked the guy about 2224 copper he laughed and said they don't have copper that big.

Second question: Does the wire have to run thru conduit between the two panels? I can already guess the answer to this one, but as the install site is already drywalled I'd like to avoid too much demo. If conduit is required, will a 3" straight section thru a stud between the two panels work using the side punch outs?

Third question: Relates to the drywall question above... Would it be safe or acceptable to wire nut the existing dryer circuit lines in the main panel thru the connecting conduit to the new location in the sub panel?

Fourth question: Does the #6 wire from the subpanel to my hot tub(the motivation for installing subpanel) GFCI box need to be in conduit, or can it just run thru the walls like romex?


Answers, corrections and clarifications on any of these points would be appreciated.

JGarth 08-28-2007 12:09 PM

Did you consider getting a larger 200a panel.
You canget a 200a panel with a max of 40 slots..
150a panel with 30 slots......
125a panel with 24 slots...
typical 100a panel has 20 slots..
These figures are in addition to the main circuit breaker.

Then, we'll look into your initial questions...

nebulous 08-28-2007 12:39 PM

I did consider a longer panel but the cost/benefit ratio didn't work out, and thats something that I most certainly would hire a professional to do. I needed one additional circuit and wanted to learn a little something in the process so I decided on a sub panel. I realize of course that the ideal solution would be a 40 slot main panel, but a sub panel fit my particular constraints better.

comp1911 08-28-2007 01:03 PM

Good luck with your project. :thumbsup:

martyshel 08-28-2007 01:24 PM

I just did the exact same thing, but my main and sub were both on the outside of the house. You'll have to get the wire from an electrical supply house (I got mine from Dealer's Electric, don't know if they have one where you live). I did run my wire through 1-1/2" conduit because it was outside, but I don't know about inside panels. I wouldn't think so because conduits main purpose is to protect from moisture, shouldn't be an issue in the wall.

nebulous 08-28-2007 02:04 PM

I assumed (and this is why I'm asking on this forum, assumptions can be dangerous) that I could run the wire right thru the stud to the subpanel, but after seeing com1911's nice looking work with his panel using conduit, it got me thinking I might need to use it. I'll look into electrical supply houses in my area (Northern Virginia), I'm sure there are plenty of them around. Keep the advice coming guys, I've learned a little from reading this and other forums, but a little knowledge can be a dangerous thing. Any other specific answers to those four questions would be helpful.

HouseHelper 08-28-2007 02:07 PM

Q1: You can get the #2 wire from an electrical supply house. Or you can use the 2-2-2-4 Al cable and a 90A breaker.

Q2: If individual wires (THHN), then conduit is required. If cable, then no conduit is required. The straight section of conduit will work, but getting the side knockout out of the exsiting panel will be difficult.

Q3: Yes. If your dryer circuit a three wire (H-H-N) then it can not be run from the subpanel. Only four wire (H-H-N-G) are allowed from a subpanel.

Q4: Same as Q2.

nebulous 08-28-2007 02:30 PM

"Q1: You can get the #2 wire from an electrical supply house. Or you can use the 2-2-2-4 Al cable and a 90A breaker."

The only reason I went with a 100A breaker for the sub panel is my friend had one that he gave to me. Would I be able to run two 50A circuits from the sub panel over a 90A feed breaker and still have room for a random 15A light or socket circuit in the future, or is this as I suspect highly dependent on the types of devices being driven?

Q2: If individual wires (THHN), then conduit is required. If cable, then no conduit is required. The straight section of conduit will work, but getting the side knockout out of the exsiting panel will be difficult.

Yes the hot tub circuit consists of 4 THHN cables, so I'll get some conduit behind that drywall before I pull the wire thru.

Q3: Yes. If your dryer circuit a three wire (H-H-N) then it can not be run from the subpanel. Only four wire (H-H-N-G) are allowed from a subpanel.

I believe the dryer is indeed a 3 wire. Thats unfortunate because the dryer breaker was in a convinient spot and was the lowest amperage 240v breaker in the main panel. Would the same thing apply if I were to move my water heater, range, or furnace circuit over?

nebulous 08-29-2007 02:18 PM

What to move over
 
I guess the reason for not putting a 3 wire dryer circuit in the subpanel is it would effectively bond N and G at the subpanel which is a no no, this is why I'm on this forum, I would have probably never thought of that.

Would it be acceptable to move two previous 15A light/outlet circuits over to the subpanel thru the two panel's connecting conduit?
If it is acceptable, should I move the existing neutral/grounds over to the subpanel neutral and ground bars, or leave them alone in the main panel?

If it is not acceptable, what two pole device would you recommend to move from the main panel to the subpanel where choices are:
  1. Furnace
  2. Heat pump
  3. Range
  4. Hot water heater
Thanks for everyone's expertise in the matter

JGarth 08-29-2007 02:41 PM

Possibly time to review the data used for that cost/benefit analysis.

That 40ckt panel is the proper and safest manner to go. And you really don't need a contractor for that. Prep the new panel ahead of time...ie, remove the LARGEST KO's ...install LARGE romex clamps for the service cable and all the branch ckts.

1)Turn off the main ckt brkr...ie,.. turn off all load in the house....
2)Pull the meter (glass portion), so it won't arc and havin' you go kah-kah in your pants....
3)Remove the mains, neutral, and grd service conductors from your main service panel...
4)LABEL...and remove all the branch ckt conductors..
5)Run an extension cord from your neighbors so you can have lite and power tool capability...also so he can watch and %$%$^%....

Pull the required permits, have it inspected, and your loved ones sleep safer at night.

Remember frugal is OK ...... foolish is well .....
Please keep us informed on this ..... it's gettin'.....


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