Subpanels (Yet again)


Old 02-19-06, 03:53 PM
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Subpanels (Yet again)

Pair of questions on sub-panels. I've been lurking for some time and think I've answered most of my other questions very completely! (Great info here)

Background info: 150 Amp Sylvania main panel with a GE sub-panel that will only be handling a hot-tub (that was double-tapped into a breaker on the main when I bought the house) and 3 recepticals for a garage that was provided with none (but -- I won't rule out future projects).

If the subpanel is going to be located below the main ( in this case in a closet that only houses the main panel -- only about 6 inches deep ) can feed for the sub run from the bottom of the main into the top of the sub. I know that in theory, I should run everything back out of the top of the box, but going six inches or so to the sub panel it seems best and neatest to run straight from the bottom of the main into the top of the subpanel. (Of course any circuits for the sub will leave from the top of the sub and go where they need, not running anything else up/through the main). Any NEC codes saying that can't be done where it would seem good practice?

Is there a formula for determining how large a sub panel can be run off of a main? I'm not pushing it, 125Amp rated sub box, but pulling from a 70Amp breaker. (Wiring is consistant with 100Amp just in case I ever needed to up it) Just curious.

Would proper practice (i.e. neat and professional) be to move the breaker for the subpanel to the top of my main box, bumping the others down, so the large amp breakers are all clustered near the top? The box has two other large breakers near the top (60A and 50A -- A/C and Range, I believe) then the 20A and 15A breakers for the household circuits with a couple of free slots at the bottom. Although easiest is to slap the breaker in the bottom, it just looks like it should be up with the others -- I'm guessing there isn't a code section relating to it, but I'd guess there is something considered "proper practice??"

Thanks for the input! Hope I'm heading in the right direction anyway.
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Old 02-19-06, 05:44 PM
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Location: Williamsport and Blue Bell, Pennsylvania
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Positioning of the panels on the wall is governed by the code. If putting the sub-panel below the main panel is the only practical place to put it, then that is where it goes.
THe NEC does govern placement of panels, however where the large knockouts on two panels are has the most influence if you intend to have a straight piece of conduit between them and do not have a large knockout punch.
Cable can enter any side of the panels, bottom is just as logical as the top.

The subpanel circuit could have the same rating as the main breaker if it is the only circuit. Really all you are doing is expanding the main panel into a second box, with a maximum of 70a allocated to it.
Your second paragraph indicated that the overall purpose of this project is rectifying the existing code-violations of double-tapping.

Do NOT move all of the breakers, little good comes out of this. If most cables are already coming in at the top, them simply put the new breaker at the bottom to keep the large wires from further cramping the top of the panel. There is no standard for where 2 and 3 pole breakrers are placed throughout the panel. Some individuals do prefer to put high-amperage breakers at the end of a buss nearest the origin of power, but that is nothing more than a preference. I think layout of wires, ease of accessibility, and logical layout of circuits is more important than sorting them by descending amperage.


Last edited by green jacket; 02-19-06 at 06:15 PM.
Old 02-20-06, 03:52 PM
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Thanks for the quick response. I was thinking that from my reading the codes did leave some room for "what makes sense." Such as in this case where there is no room to the top, left or right of the main panel for a sub (essentially they framed a door over the panel when they sheetrocked). And, although I could run the feed line up to the top and then all the way past everything back to the breaker on the botton -- it just didn't make sense.

However, I know enough to believe that just because I don't see the logic to ask!

Thanks again.

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