# When to use sub panels in residential construction?



## L. B. Condulet (Aug 23, 2007)

What factors to you guys take into account when making the decision to use a sub panel in a new home? If I'm wiring a house with a large, fully equipped kitchen I may use a sub panel in an effort to reduce the labor needed to run all the home runs, especially if the kitchen is on the other side of the house.

The benefits of sub panels are shorter home runs and perhaps less voltage drop in certain cases, the disadvantages are the cost of the panel and the feeder, also you need an inconspicuous place to install the sub panel.

Do you guys have a rule of thumb? Like "20 or more circuits merit a sub panel"...

Do you add up the collective costs of your home runs and when that cost exceeds the cost for a sub panel, you opt for a sub panel? Is the decision to install a sub panel always strictly economic or does usability play a role in the decision?

Do you ever add a sub panel because you simply have run out of spaces in your main panel?

Thanks!


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## mdshunk (Mar 13, 2005)

My rule of thumb is that if I have at least 6 branch circuits in a certain area who's home run would be 75 feet or more, I'll try to use a sub. The builder or the owner won't always permit remote subs for aestetic or design reasons, which is fine. There's some benefit to having all the mechanicals located in one place, and there's also some benefit to distributed subs. It's hard to put a finger on when to use them and when not to. Some houses are so cut up, that running home runs to certain areas becomes difficult. In this case, a sub makes perfect sense.


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## MechanicalDVR (Jun 23, 2007)

We always added one to mechanical rooms on large houses, it is just easier when the main panels are elsewhere in the house.


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## MSSI (Mar 25, 2006)

If the house is over 2500 square feet. There is a real good chance I am going to use a subpanel


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## BigMikeB (Aug 1, 2007)

If it cheaper to run one larger wire and install a panel and breakers than it is to run several home runs back to the main panel. I have put them in garages, basements, and laundry and utility rooms on some of the mansions I have worked on in the past. I would say it's common place in a house that has a 400 amp main to use several.


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## Magnettica (Dec 19, 2006)

It often depends on if the builder or HO is willing to pay for the new panel. Sure it makes it easier on the electrician, but it usually comes down to who's going to be paying for it. I'll also go along with the over 2500 sq. ft. opinion.


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## jbfan (Apr 1, 2004)

Most of my work is in remodeling.
I use subpanels almost every time I work on a basement. The main is upstairs in the garage, and the basement is the size of the house, even if there were enough slots, just not worh the hassle.
I have also put many subs in because of lack of spaces.


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## itsunclebill (May 18, 2006)

:w00t:


Magnettica said:


> but it usually comes down to who's going to be paying for it


If it isn't the customer you're in the wrong business. 

I think MD has it pretty well nailed, although I look pretty hard at ANY situation where 5 or more circuits are involved regardless of home run length. If the main panel is outside it's almost a sure deal


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## 747 (Jan 21, 2005)

When your going to install a natural gas back up generator on a house. That requires a subpanel or at least i think it does.:clap:


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## mdshunk (Mar 13, 2005)

Another reason to use a couple of subpanels, distributed around the home, can be to limit voltage drop. I really don't get too excited about VD in a dwelling, but some of these really big houses can experience some VD at the further parts. Home inspectors get people all fired up about voltage drop, even though it might not be that big of a deal.


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