Yet another Subpanel Question

[Anthony Whitesell]

or two.

Does it make sense to run a 60 amp subpanel off of a 100 main panel? Something in my EE head says that's a bit goofy and pushing the limits of the breaker and panel. The main is full but includes two circuits for the 120V air compressor, 220V bandsaw/jointer which would move to the sub panel.

Is a 60A subpanel and breaker sufficient to run a 220V 20A circuit for the DC, a 220V 20A circuit for the bandsaw/jointer, 120V 20A for the air compressor, and 120V 20A for the TS/Router/tools/etc? By my math that's a nicely balanced load of 60 amps on each leg but also at the breakers maximum.

Lastly, a recent panel upgrade post got me thinking of an idea of handling the frist question if I have to upgrade to a 200A service. Could I install a small 200A panel next to my current 100A panel, and power the 100A from the 200A and effectively turn the present panel into a subpanel?

[Robert Reece]

You listed 60A of tools, but you don't run them all at once do you? You must produce 6 pieces of furniture a day.

Seriously, you should only add up the power of the stuff you intend to run at one. It sounds like 2 tools at 220V 20A. So that's 40A coming down a 60A wire. Not a problem.

I would actually go with your last suggestion of adding a 200A main panel and then converting the other one to a sub. That might be somewhat painful though because the existing 100A panel will have to have all neutrals and grounds on separate bars. If it's a main panel, they may have run the ground and neutral to the same bar.

One last thing, if you do put in a 60A subpanel, I would size the feeder wire for 100A to give you options later. For that matter, just put in a 100A panel. 100A sub from a 100A main is ok. I have a 200A sub off a 200A panel.

[David G Baker]

Anthony,
I have a 200 amp main panel that has two 100 amp breakers in it that I use to power 2 100 amp sub panels in my basement. This way I can work on circuits coming out of one panel and still have power out of the other to run work lights and power tools while I do re-wiring in my home or detached buildings.
I have at least 5 sub panels on my property and never worry about overloading my main panel.

[Thomas Syrotchen]

Based on the equipment you listed, I think it is likely you would have three pieces of equipment drawing current at one time the DC, compressor and Bandsaw all on one leg. You may want to review recent posts on how to size subpanels. Essentially, use the NEC tables (I think its 430.52) to determine the FLA based on your motor sizes. Sum all the FLA's and add 25% of the largest motor. I'd be willing to bet your total load is under the 60A figure you list as its likely your branch circuits are oversized to accomodate startup on each motor.

However, 100A main service seems small these days even if you're only talking a 50A draw on that equipment. It won't take much else in the house before you're tripping the main. Turn on the stereo, have the AC going, wife using a hair dryer and you in the shop and I wouldn't be suprised if you trip that main.

Just another thought, from a resell standpoint, would you rather have a single 200A panel for the house or three seperate panels? By the time you buy a 60A sub and a small 200A panel to feed both, you could probably just buy a single 200A panel with several breakers at the same cost. I know personally, If I walked into a home with three panels, and one feeding another like you describing I'd be nervous. I know electrically there may be nothing wrong with it, but for the average homeowner are they going to want to mess with it?

[Anthony Whitesell]

I hear what your say Thomas. From a cost standpoint, It probably makes more sense the way I described 200A main feeding 100A and 60A subpanels so I don't have to completely gut and remove the old 100A panel. In addition, I figured out that it costs just as much to run the 60A and shorter runs for the circuits as it is to run the circuits individually all the way across the basement. I will probably still do the 60A so it's neater.

Thank you all for letting me know that it's possible. The debate is now, 200A main upgrade or 200A main add-on. But I don't have to worry about that until I find a good 220V 2HP minimum DC of CL locally.

[Tom Godley]

First thing to look at is what you have in the house. 100 Amps is actually a lot of power. It becomes a problem when you add resistance loads -- stoves/ ovens/ dryers and baseboard/ heat-pump electric heating.

So depending on what is currently in the house will determine.

You do understand to install a new 200 amp panel requires new wires outside as well as a new meter pan and often will require new wires to the pole or wherever the house now gets its power.

I had a situation once where I wanted to do just as you said -- add a new panel and then feed the old original panel next to it -- I was not allowed to do this. But another time I was - so you may need to check.

I installed a 200-amp panel in my current house -- although I will never need anywhere near that much power. The 200 Amp panel kits are cheaper than trying to go with a 150 Amp. Same goes for the 100 Amp panels w/o main breakers -- that is why they are often used as subpanels. You can feed them with 60 Amp breakers and wire.