Thanks to sierraeast for straightening my goof-up out & Bill,that's a pretty good detailed work-up about what I've got planned. I'm going to study it at length,but you confirmed my basic original thoughts about how to accomplish this. Your charts and guidlines will be very helpful as I fine tune this. The point about installing the panel in the garage/interior wall cavity was a great heads-up....I was going to do just that. If I surface mount the sub panel in the garage on top of the firerock(perhaps in a firerock plenum) then I should be OK ? I had planned to run all the garage wiring in conduit anyway. I should add the additional rooms(12' firewall between the garage/shop & living area) will be 8' ceiling height in an area that is 12' tall(this leaves a 3&1/2' loft/storage area above those rooms). This will also make those areas easier to wire/insulate/& run HIVAC plumbing. Thanks very much for the information.... back to the drawing board..LOL...Dave

Questions?-- We are converting it to a dwelling by adding 3 BR & 2 baths which leaves a 24x32 shop/garage in the back 1/3 of the structure.All the wiring already installed is in flexable conduit,but the 200A panel is up front & I want to rework the 70A sub panel by installing a 100A panel about 40' back from the 200A main and replace the existing 70A breaker with a 100A to feed the new sub panel. Whether you can protect the #4 individual conductors (I'm assuming they're THHN) with a 100A breaker is "iffy" because it may depend on local code interpretations. In some jurisdictions you can use #4 for 100 amps for indoor subpanels. In others you'd need to upsize to #3 copper. (The latter would be true where I live, BTW.) Best to check with your AHJ (authority having jurisdiction--the local permit/inspections office) to be sure. This will allow me to make short runs to feed the additional rooms and have the panel in the shop/garage where I want to have a 220V welder plug close to the 100A sub panel.I'm trying to avoid making all those homeruns from the front of the building to the back as well as having control over the shop feeds right in the shop area. Makes sense to me. The existing 70A sub panel is three #4 separate copper (AWG) wires...Will this feed the 100A sub panel? I also have a good amount of #3 copper of the same type,if that will be better. If I had sufficient #3 on hand, that's what I'd use. (If I'm interpreting your info correctly, you'll be moving the subpanel further to the rear of the building. Thus, I'm also factoring in the advantage of not having to splice the old wires in an junction box located in the middle of the run. However, I'm not certain I understand your plan. When say "rework", does that mean you'd leave the existing 70A subpanel in place and have it feed a second subpanel? Or do you plan to move it altogether? Just want to be sure...) Would it be better(correct) to run 4 wires (H-H-N-G) or 3 wires? This is all inside the structure. Yes, it would be better (correct) to use 4 wires with separate neutral and grounding conductors. So called 3-wire feeds are legal only in certain circumstances for detached buildings. But even in that context, they are being phased out by the 2008 National Electric Code. The grounding conductor can be smaller than the hots and neutral. In this case you should be able to use #8 bare or green, although that's also worth verifying with your AHJ. Whether you reuse the old subpanel or buy a new one, when wiring a 4-wire feed, you need to fully separate the neutral (grounded) conductor from the grounding conductor. The neutral feed and all branch neutrals should land on the neutral bar. The grounding conductor and all branch equipment grounds should connect to a separate ground bar. (You may have to purchase a ground bar separately--usually under $10.) You also need to remove any bonding connector from the neutral bar to the box and/or...

You now have only a 20 slot 200A panel. That is way too small, so you'll have to add a sub panel. I suggest a 100A sub. Remove the 30A DP dryer breaker and put a 100A DP breaker in its place to feed the sub. Then run the kiln, dryer, and anything else off the sub.

Wayne, Thanks for replying. 1) I was adding another circuit to the main panel later in the day of my original posting, so I checked the heater circuit. It was 5kW, not the 3kW I originally posted, but it's in addition to the heating element installed as part of the HVAC (probably wasn't clear in my original post)... the cost was $100 if I had the extra circuit installed by the time they put in the main HVAC unit, so I said "why not". This is the circuit I think I can now do away with as it's not needed with the new pellet stove keeping us warm. The "standard" heating element in the HVAC is now the "emergency" element, if you will. 2) So you're suggesting bringing a short main panel circuit outside to the transfer switch, thereby allowing for a single long run from the switch to the subpanel. Hmmm, that idea has a lot of merit. I would definitely want to go with an ATS, then, so I don't have to walk outside to swap things out (and shoveling snow to get to that side of the house... like the 4' we had in 3 days last year :( ). 3) I'll read it after posting this... 4) I was thinking of a Kohler or a Cummins-Onan, though I hear Kohler is often more expensive in the long run because they do their best to force you into using their own guys for general service. In that case, Cummins-Onan has a serious edge.