Basement Finish. Sub Panel or no?

bakerz1January 4, 2010

I am finishing my basement and am trying to decide how to handle the electric service for the basement. The builder was kind enough to supply the blue flexible conduit from the main to the basement. After thinking it over I believe I have 2 choices.

Either run all the circuits through the conduit to the main panel or run a sub panel. I have enough slots in the main panel to add all the circuits I need.

My main panel is 100 amp, and is in the garage with the mentioned conduit. It wouldnÂt be difficult to get another conduit through if need be.

The circuits I will have in the basement are as follows

*#1 Bar Microwave GFI 20A with 12-2 wire 1 outlet

*#2 Bathroom GFI 20A with 12-2 wire 2 outlet 1 fan 1 lg can light 3 small can lights

*#3 Bar GFI 20A 12-2 wire 5 outlet

#4 AF Bedroom outlets 20A 12-2 wire 7 outlet

#5 AF Bedroom/Fam Room lights 15A 14-2 wire 1 std light 8 lg can lights

*#6 Main Lighting 15A 14-2 Wire 2 lg can lights 3 small can lights 3 std lights

*#7 Main Outlets 15A 14-2 Wire 8 outlet

The location for the sub panel that makes the most sense is in furnace room approx 65 feet away from the main panel, (by most sense I mean easiest to get code clearance, and central to 5 of the 7 circuits. * Starred circuits are central to the proposed sub panel.)

I wouldnÂt be honest if I didnÂt say I wasnÂt on a budget here so I guess cost is 70-80% of driving force, and 20-30% is convenience of installation.

What I have been told is that I would use a 100amp sub panel and set it up for 50 amps. I have also been told I can use Alum #6-4 SER to make the run between my 100amp main and my 50 amp sub. However I have had some arguments come up that at 65ft of cable run I loose too much power to give 50 service at the sub. I know copper is easier to use but remember IÂm on a budget and from what I see the copper choice is approx 3x more expensive and seems to price me out of the sub panel choice.

I am open for suggestions.. Please tell me if this was you doing the job, which choice would you make and why and what cable you would use between the main and sub. Also let me know if you see flaws in the logic IÂm using here for the circuits etc..

Thank you so much for all the help.. Matt

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Need more information to venture a guess.

First: what SIZE (diameter) is the blue flexible conduit run from the main to the basement and does it run under the garage slab?

Depending on the diameter you may not be able to run all conductors through it without derating each circuit circuit. This may not be practical or achievable. Size of conduit/raceway depends upon the number of current carrying conductors.

If the conduit is run under the garage slab, your conductors would also have to be rated for use in a "wet" location. (All underground locations are considered 'wet')

Second: Under what electrical code does your jurisdiction operate?

If it is under the 2008 NEC, then EVERY circuit in a habitable room (except for those with GFCI protection) anywhere in the house would need AFCI breakers. This would mean AFCI breakers not only in bedrooms, but also for lighting in all locations considered habitable, and for all general purpose and lighting circuits in any other habitable room. (Dens, Rec rooms, offices, halls, closets,. etc)

THIRD: What about hard wired, interconnected smoke detectors? Most codes require at least 1 in all basements, 1 in each bedroom and at least 1 immediately outside all bedroom areas. You didn't mention any in your 'outlet' calculations I don't think.

LASTLY: What is your heat type? If electric, you need to factor in loads.


Provide more information and perhaps someone can help.

    Bookmark   January 4, 2010 at 11:11PM
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You won't be able to pull SER though a conduit run much less any cable (especially in smurf pipe) Plus it is against code to pull cable in pipe unless it is a short section to protect it from damage. You will have to junction box the other end of the smurf in an accessible spot. Then run individual THHN or THWN wires, changing to cable for each circuit at the junction box. Same goes for if you do a panel, you'll need to use individual wires and extend the smurf pipe all the way to the sub panel location. To be minimal, a 40 amp sub panel would be ok. You would then use #8 copper or #6 aluminum.

    Bookmark   January 4, 2010 at 11:31PM
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Ron Natalie

Even "in" the slab is a wet location.

If it's smurf pipe I hope it's decent size. Pulling stuff in that is going to be fun.

    Bookmark   January 5, 2010 at 11:41AM
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I don't see anything about being under the slab. But yes that would change the wire requirements and wouldn't allow smurf pipe anyway.

    Bookmark   January 5, 2010 at 7:09PM
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Thanks for the responses. First of all, the main panel is in the garage but right next to the wall that joins to the basement. The only material that the current "smurf pipe" passes through from the main panel and the basement is the floor joist. So making more raceway capacity is not an issue. There is enough space in the floor joist to run each circuit through its own drilled hole, or I could drill a 2 inch hole for #6SER if I need to. So getting either 7 circuits or a large cable through the one floor joist is not the issue at all. To be clearer there is no concrete involved in this run. The raceway would pass only through the floor joist and possibly one stud. More than anything I was wondering about the last paragraph.. What would you do if you had an accessible main panel to run circuits up to 80 feet away? A sub panel or run them individually? If you had to do a sub, what would you use for that distance for cable and amps?

    Bookmark   January 5, 2010 at 8:51PM
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Ron Natalie

The issue is:

Do you want to run all those individual circuits back to the garage? is there enough breaker positions left in the main panel?, how much does the wire in various sizes go for in your neck of the woods? Is there room in the pipe for all that wire (almost certainly not for the individual circuits and there are derating issues)...

There's no real advantage or disadvantage to a subpanel over all here, you just have to look at the bigger picture as to what would be cheaper or more convenient for you.

Subpanels typically start around 60A and I think that's probably a reasoanble size for what you envision.

    Bookmark   January 6, 2010 at 9:57AM
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I would install the subpanel using 6/3NM, fed from a 60A breaker. As long as your load does not exceed 55A (and it should not), this is allowed. At the distance you describe, voltage drop will not be an issue.

    Bookmark   January 6, 2010 at 10:36AM
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Thank you very much for the responses. Now I have been told that Alum is a legit choice for this vs copper which is 3x more. Aproxx $210 vs $75. I have heard this is a bit tricky but is suitible for this application.

    Bookmark   January 6, 2010 at 1:25PM
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