Sub-Panel questions

[Jay Maiers]

Hey folks,
I want to install a sub-panel next to the existing house panel. I'd like to run 100A service to this panel to cover general lighting, a smallish wood working setup, and a pottery kiln.

1) Am I allowed to run power out through the bottom of the existing panel, throught the stud, in through the bottom of the new panel, and up to the main breaker lugs at the top? (I'm planning on using 2-2-2-4 Aluminum for this connection)

2) I picked up a Siemens panel that looked like it would fit my needs. During test-fitting, I found that the door for the new panel overlaps the breakers on the first panel. Will this pass inspection, or do I need to find a different panel (with a narrow door)?

Thanks!
Jay M

[Rob Steffeck]

I just finished wiring my shop a few months ago and did something very similar, except I skipped a stud bay. So my 100A sub is 16" away from my main panel. I used #2 NM-B copper feeder from the main using a 90A breaker (#2 copper is rated at 95A, aluminum is less...75A I believe). I routed the feeder out of the bottom of the main panel, through the stud, up through the empty bay, through the stud, then down through the top of the sub-panel. Can you skip a bay and go this route?

If not, you could always mount the subpanel upside down to avoid taking up the space inside the sub by routing the feeder through it. If your sub is a main lug, then it shouldn't matter at all to mount it upside down.

The door / trim overlap sounds like it may be your big problem. I know the panel covers for my main and sub would not allow them to be in adjacent stud bays even if I wanted them to.

[Dan Friedrichs]

I'm not a code expert, but there is nothing technically wrong with what you suggest.

However, is this work going to be subject to inspection? If so, you should simply ask the inspector these questions, because his opinion is what matters, and his opinion may not even agree with code.

As Rob said, since you won't have a main breaker in the subpanel, you could mount it upside down if that's more convenient.

Since the run between panels is so short, consider using copper wire, instead. The smaller size (for the same ampacity) will be a huge help when trying to route it.

[Jay Maiers]

I routed the feeder out of the bottom of the main panel, through the stud, up through the empty bay, through the stud, then down through the top of the sub-panel. Can you skip a bay and go this route?

If not, you could always mount the subpanel upside down to avoid taking up the space inside the sub by routing the feeder through it. If your sub is a main lug, then it shouldn't matter at all to mount it upside down.

Thanks Rob.
I can't skip a bay. The existing panel is near the outside wall of the basement; the next opening is the only one on that wall that will fit the panel. I could run the feeder past the panel, up the wall, and back through the stud, but that seems a bit absurd. Your suggestion about turning the panel upside down is a perfect answer to both issues if it's permissible. I don't see why it wouldn't be, but who knows?

Dan, this will be inspected bofore it's all over. I'm really in my planning stage (new house, big basement playroom ); I bought the panel to help visualize the issues, and so that I can get going ASAP. I have exactly one outlet and five lightbulbs in a 1000+sf basement

I'll look at the copper wire. Can I pull individual wires, or does this have to be a bundled cable? From what I've read, individual cables seem to be a legal and reasonable way to go, but I'm very new to this level of wiring.

[Don Jarvie]

Do you know an electrician that could answer a few questions? I don't see why you can't go in from the bottom (I'm not an electrician) since they have knockouts in the bottom. If it was against code then they wouldn't make holes in the bottom.

[Dan Friedrichs]

Your local building inspector's office should be able to answer these questions for you easily. If it didn't require inspection, I'd do it exactly as you want, but since it does...

I'll look at the copper wire. Can I pull individual wires, or does this have to be a bundled cable? From what I've read, individual cables seem to be a legal and reasonable way to go, but I'm very new to this level of wiring.

Will there be conduit between the boxes? If so, use individual wires.

[Rollie Meyers]

Hey folks,
I want to install a sub-panel next to the existing house panel. I'd like to run 100A service to this panel to cover general lighting, a smallish wood working setup, and a pottery kiln.

1) Am I allowed to run power out through the bottom of the existing panel, throught the stud, in through the bottom of the new panel, and up to the main breaker lugs at the top? (I'm planning on using 2-2-2-4 Aluminum for this connection)

2) I picked up a Siemens panel that looked like it would fit my needs. During test-fitting, I found that the door for the new panel overlaps the breakers on the first panel. Will this pass inspection, or do I need to find a different panel (with a narrow door)?

Thanks!
Jay M

#2 AL is only good for 90 amperes, since it is not a residential main service you are not allowed to undersize your conductors, subpanels, feeders to outbuildings must use full sized conductors. You must use table 310.16 for sizing conductors,table 310.15(B)(6) does not apply.

Here is a copy & paste from the 2008 NEC which is unchanged from the 2002,2005 editions. 310.15(B)(6)

(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services
and Feeders. For individual dwelling units of onefamily,
two-family, and multifamily dwellings, conductors,
as listed in Table 310.15(B)(6), shall be permitted as
120/240-volt, 3-wire, single-phase service-entrance conductors,
service-lateral conductors, and feeder conductors
that serve as the main power feeder to each dwelling unit
and are installed in raceway or cable with or without an
equipment grounding conductor. For application of this section,
the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies, either by
branch circuits or by feeders, or both, all loads that are part
or associated with the dwelling unit. The feeder conductors
to a dwelling unit shall not be required to have an allowable
ampacity rating greater than their service-entrance conductors.
The grounded conductor shall be permitted to be
smaller than the ungrounded conductors, provided the requirements
of 215.2, 220.61, and 230.42 are met.

[Tom Godley]

Is the main panel short on open spaces?

If you have two extra open spaces I would run the kiln directly off the main panel-- this would allow for a smaller sub-panel.

100 amp is a lot of power.

[Jay Maiers]

Is the main panel short on open spaces?

If you have two extra open spaces I would run the kiln directly off the main panel-- this would allow for a smaller sub-panel.

100 amp is a lot of power.

Tons of physical space available, but they used the slimline breakers and have taken all but two or three of the ground and neutral openings on the bars. I could probably get by with 75 or 80A, enough for the kiln, the lights, and a couple of utility outlets.

[Dan Friedrichs]

You have room in the main box, but are just short on lugs for the neutrals and grounds? You can move those neutrals and ground around and place more than one in each screw hole (if there's room). You could also add additional bus bars for more neutral and ground connections, and bond them to the existing neutral and ground bus bars.

[Jay Maiers]

#2 AL is only good for 90 amperes, since it is not a residential main service you are not allowed to undersize your conductors, subpanels, feeders to outbuildings must use full sized conductors. You must use table 310.16 for sizing conductors,table 310.15(B)(6) does not apply.

Huh. Thanks Rollie. Looks like I was working off of the wrong table. I'll have to decide if I want a true 100A at that panel or not.

This is the first time I've had to apply for a permit. Since I'm not familiar with the process, I'm trying to knock out all of the reasonable questions / "get my ducks in a row" before setting up any appointments.

Thanks everyone.
Jay M

[Tom Godley]

The point of placing the kiln directly on the main is it would eliminate the need to plan for the load on the new panel. Since the panels are close to one another what is the need for the kiln on the sub

You can add bars to increase the spaces for the neutrals and grounds-- but you still must say within the listed maximum number of circuits on the panel

[Tom Vanzant]

Jay,
Are the lugs compatible with aluminum wiring?
Tom

[Darryl Hazen]

Before you use aluminum wiring do a Google search for "aluminum wiring dangers". You may want to reconsider. I owned a house in CA where aluminum was permitted. Three home in the area burned to the ground within a year. Fire inspectors findings: aluminum wiring. If I were you I'd bite the bullet and use copper.

[Roger Jensen]

100A is a lot of power. Are you going to be running multiple heavy machines simulaneously? I ran a 60A sub-panel in my one-person shop and have never been short of power. If you're adding that much you may need to upgrade the lines to your house. Do you know how much capacity the lines to your house have?

Roger