Two 100A sub-panels from a 200A sub-panel??

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  #1  
Old 03-30-06, 06:49 PM
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Two 100A sub-panels from a 200A sub-panel??

OK.....I have a 400A main....Two 200A sub-panels.....I have some long (over 150') runs from those sub-panels. I am planning one 100A sub-panel from a 200A sub-panel. In a previous thread I had regarding MWC, a second 100A sub-panel from the same 200A sub-panel would be my best solution. Can I safely and to NEC code install 2 sub-panel from a sub-panel??
 
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Old 03-31-06, 09:42 AM
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What are your connected loads on each panel (existing and proposed)?
 
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Old 03-31-06, 06:35 PM
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I dont know how to do the calcs but I had my 400A system engineered (per city code) and both of the 200A sub-panels engineered out at a total of the two at 267A. I want to add a 12 breaker 100A sub-panel from one of my existing 200A sub-panels. The 100A panel will have 1 outdoor GFCI circuit, 3indoor outlet circuits, 3 lighting circuits and 2 pool pumps 3/4 hp motors. The existing 200A that I will pull from has 1 60A A/C circuit, 9 outlet circuits plus 6 dedicated kitchen outlets. A 20A for the washer, 20A for the frig, 20A for freezer, 20A for dishwasher/disposal, 30A 240 for the dryer and 10 lighting circuits. 1 dedicated circuit for smoke alarms. Not sure if this will help all that much. Thganks for any help.........
 
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Old 03-31-06, 06:45 PM
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There is no limit to the number of subpanels you may have. If you wished, you could run a separate 200A subpanel for each and every room of your house (though you couldn't place the bathroom subpanel _in_ the bathroom

However there is a real limit to the amount of _power_ that you can use. This is set by the ratings of all the components supplying a given subpanel, and how much power is going to other subpanels. If you have a 200A panel, and you use it to feed 10 separate 200A subpanels, then you are still limited to 200A total consumption.

What the NEC mandates is that you do a load calculation to determine how the panel will be used. For residential applications, this load calculation takes into account things such as the size of the home (square feet), particular required circuits (kitchen appliance circuits, etc), specific fixed loads (water heater, central air, pool pumps, electric ranges, etc) and tells you how much power must be available. These calculations take into account that not everything will be on full blast all the time.

Once you have provided a sufficient supply and panel, then you can choose to distribute this power any way you wish, as long as at each step of the way you meet the minimums.

Say you calculate that your home needs a 150A service. You install a 200A service to allow room for expansion. This will likely be a 40 circuit panel, and there will be a couple of 50A breakers (range, spa), a couple of 30s (hot water, dryer), a few other large loads (AC) and a bunch of 20A circuits for lighting and receptacles. If you total up the entire possible load (all of the breaker values), then you will likely have 600-1000A of total circuits. But this is totally fine, since the calculated load over time is only 150A.

If you wish, you could put in a bunch of subpanels (as suggested above), and then in the main panel you might have a total of 2000A of breakers. But because this is still the same house with the same loads, the service would not be overloaded by the different electrical consumers.

What you need to do is to calculate the total load that your home requires (with the new additions). You then need to calculate the load served by the 200A panel in question, including the new circuits. If this panel will not be loaded in excess of 200A, then you can connect this subpanel. Finally, you need to evaluate the load placed on the new subpanel, to see if it is sufficient.

Search for 'demand load calculation' and you will find a good number of references on how to do this.

-Jon
 
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Old 03-31-06, 07:36 PM
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Jon.... Great post and advice.... Thanks
 
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Old 03-31-06, 08:27 PM
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Good post Jon.

From the hip, I'd say go for it.

But use a 125A 20/30 space panel. No sense in filling the panel right outta the gate.
 
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Old 03-31-06, 08:52 PM
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Thanks all..... I checked the calcs but have figuered I am not really adding any more load than my engineer figured. They did calcs for the house factoring in the addition, so same load, different amount of subs/breakers..... thanks again
 
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