I was just wondering what some standard sub panel runs are. It seems that the 6/3 used for an electric range is a good wire for a 60 Amp panel but what's the next jump up?

I have to sit down and do the math but it I think a 60 amp panel should be fine for my 2nd floor sub. Even derated to 50 amps for heat and voltage drop that's still a lot of current for general lighting and outlets plus one bathroom. As I mentioned in a previous thread, my house is a nightmare to fish new wires so I want to pull the smallest copper I can, but not so small that I have to do it again if I need a little more power up there.

When I install central AC the air handler will be in the attic so that's the one concern but I haven't seen current draw specs for it yet. it may be easier to run a dedicated run from the main to the AC and use the sub for everything else.

 

You can do a load calculation for the upstairs. A 60A subpanel upstairs is probably more then enough. If your air handler doesn't have electric heat it will probably only call for a 15A breaker. If it does, then the load will be much higher. You can run a piece of conduit (either PVC or EMT, whether the code requires), put a big (and I mean big if you use large diameter conduit) junction box at either end, and run your circuits through there. You can run multiple circuits through the same conduit (although if you use NM-B I'm not sure if you're even allowed to run them through conduit for that long of a distance).

 

I forgot to add the answer to your question.

Bathrooms need a 20A dedicated circuit, for bedrooms I usually run a 20A circuit (each), although 15A will probably be ok also. It really all depends on what you're have running. If you plan on having window AC units then you'll probably need a dedicated 20A outlet/circuit for that location. If you plan on having a home office you may want to run a dedicated circuit for that also.

 

Thanks for the info. I do plan on doing a load calculation, I just haven't gotten there yet. I only did it once before so it's going to take some time with the calculator and the code book to figure it all out. Plus I may take the roof off and make the attic useable living space so I want to do the calculation a few different ways to see where I end up. My intention was to run a 100 Amp sub to cover any eventuallity but that was when I thought I was going to be able to punch into the wall directly above the main with a staright shot to the attic. As it turns out the walls are fully insulated with MUD & STRAW.

If I go with external conduit up the side of the house my run to the panel will be just about 40'. If I want to fish through the walls I've got to go to the opposite corner of the basement, up the walls and then back again. Probably 80'. I haven't looked to see where that puts me for voltage dop yet.

 

For a 100A sub you should probably use #2 copper. You'll need a 1 1/2" EMT (or Sch 80 PVC if allowed) from the main panel to the sub, and you'll probably need to use individual THHN cables. You'll need a grounding wire also, and a separate neutral/ground bar in the subpanel.

 

The more I think about it the more I think I'll just make the 6/3 work. When I add central AC it will most likely be at the same time as the kitchten renovation, which means walls will be open. I'll still have to calculate for temp & voltage but at 50 Amps 220V I should be OK. With two small AC window units, one bathroom, one hydroculator (1100 watts) and general lighting for 500 sq. ft. I don't think I'll ever pop the breaker or heat up the 6/3.

 

Assuming you can drill properly sized holes through the top and bottom plates it's not more difficult to pull 1 or 5 NM-B runs. Use a fish tape and pull several NM-B runs. With the exception of the bathroom you can pull 14-3 or 12-3 runs for everything else. That way you can use 1 NM-B to feed two circuits (you'll need to use double pole breakers if you do this). You may not even need a subpanel, although it's probably going to be less expensive if you do put one in. I don't know what kind of air handler you're going to put in there. I don't have any experience with heat pumps/air handlers, all I know is split AC with furnace inside the house and compressor outside. This system requires only a 15A circuit for the furnace. However, if you use a heat pump the air handler will probably have emergency heat, which needs some pretty large wires..

 

I had considered that but you'll have to take my word that it will be much harder to run a bunch of 12/3 or 12/2/2 than one 6/3 to the attic. I'm not very experienced with high voltage but I have more experience at pulling wire then I car to think about.

There is plenty of space in the 200A main panel to do whatever I want and I would actually prefer to keep it all in one panel but I leaned towards a small sub for a few reasons. One 6/3 is a lot easier to run than a fistfull of NM-B, voltage drop to the actual devices should less with a 6 ga. feed to the panel and 12 ga. drops and I can go overkill with separating the loads onto different circuits, just for convienance. If I'm pulling 12/3 I'm going to want to use as few circuits as possible. The AC will probably not be doubling for heat, I've got two year old oil burner that works fine. It is something to think about as a back up though.

I really keep flipping back and forth but a small sub just seems like it is going to be the most convenient, better results and the cleanest install. I'm pretty compulsive about trying to keep wiring as neat and clean as is reasonable.

 

Then I would go with a 50 or 60A sub. If you can use NM-B you're in luck, it shouldn't be that difficult. Make sure you have the clearances for the subpanel.