Adding sub-panel and upgrading main feed


Old 08-14-07, 06:38 AM
Thread Starter
Join Date: Aug 2007
Posts: 1
Adding sub-panel and upgrading main feed

I currently have a 150 main breaker and box feeding the circuits in my home. I am adding an attic room which will have it's own small A/C and heating unit along with a couple 15 amp circuits. My current box is full and so I would like to parallel in a 50 amp sub. However, the main lines coming into my breaker box from the meter are 0/2 gauge which is I believe is only rated for 150 amps. Not sure what the lines coming into into the meter are. So my questions are as follows:

- What gauge wire would I need to feed 200 amps?
- Would the power company likely need to run new lines to the house and change out the meter? Any idea what range of cost that might be?
- If I install the appropriate 200 amp gauge lines coming into the current 150 amp box, would I just parallel off of the main breaker input terminals and run lines over to the new 50 amp sub (200 amp total)?

Any thoughts or ideas welcome. Thankyou for your time.
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Old 08-14-07, 06:55 AM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Do you need to increase the size of the service? Have you done a demand load calculation?

Why are you adding 15 amp circuits? Do the smart thing, and add 20 amp circuits. You will eventually regret the 15 amp circuits.

Anything having to do with the incoming service is not a do-it-yourself project.
Old 08-14-07, 07:57 PM
Join Date: Dec 2006
Location: orange county
Posts: 285

I am a novice but I am of the opinion you have an incorrect understanding of several things. I'm probably not the best person to give you a better understanding but I'll give it a shot, someone else will come along. Generally when folks run out of "space in their main panel" , what you do (after you do a load calcuallation like the moderator suggested) is "make space" in your main panel (if your main panel allows it) by substituting full size breakers (if you have any?) with Mini's, quads etc. Anyway just enough room to fit in one full size breaker that will feed your Sub-Panel, wherever it is to be located. At your sub you install the circuits you desire. If your total load calculation ( including the load of the circuits you plan for your sub) does not exceed 80 percent of your 150 main breaker disconnect I think you would be O.K. I am a Novice with little experience at this sort of thing and the info I provide comes mostly from having read these posts. There is a lot involved concerning safety. I mean a whole lot of stuff you will need to familiiarize yourself with before attempting this project. It's not rocket science but the order of the day is doing it right and safety, safety safety. There is a in-expensive book at the H.D. called Wiring Simplified This is the book that is often suggested here that one should read from cover to cover.
Old 08-15-07, 08:41 AM
Join Date: Sep 2000
Location: United States
Posts: 18,497
First, do the demand load calculation to see if you will really need more than 150 amps. If you do, start by calling your power company. Only they can answer the questions about their lines. The work required to replace a main panel is normally left to a professional. An extremely experienced (and I really mean extremely experienced) DIYer may be able to do it, as long as your family doesn't mind being without power for a week or two. Panel space probably won't be a problem in this case, since you'll need to replace your whole panel anyway and you can start with a larger one.

If you do not need more than the 150 amps, according to the demand load calculation, then see if you can get the extra space in the main panel as sidecutter suggested. If you cannot free up enough for all your new circuits, maybe you can free up enough for the breaker to your new subpanel. Even if you can't free up any space at all using those techniques, you can put a subpanel right next to the main panel and move a couple of circuit to it to get the space.
Old 08-15-07, 09:57 AM
Join Date: Mar 2006
Location: NE Wis / Paris France{ In France for now }
Posts: 4,808
I will echo the above guys's comments but also it will be nice if you can get the load centre model number off it will really help us alot here as well because there are some load centres can NOT take twinner or quad breaker at all.

also just goggle " load demand calucation " it will come up pretty good number and it will expain how to do this.

with 150 amp service which that is not too super common size in some area but to order to get bigger service or " hevey up " this part genearlly is not a DIY project because the time constract and also have to deal quite few codes and i think it will be fair for other members here i dont want to list all the codes in here to steal all the space here.

For the price for changing from 150 to 200 amp tell you the truth it will not be cheap at all because each area charge diffrent rates and each electrician will charge diffrent rate just like comapre apple and orange if that make sense here ?

the most common way to is add subfeed box which that is pretty common way to add new circuits you may have to remove at least 2 circuits [ 120 v ] or dryer circuit if that is 4 wire if 3 wire leave it alone just move the other two circuits

also when you slecting a subfeed box make sure you get big engouh so you can add more circuits in future needs

if more question please do post it in this forum thanks

Merci , Marc

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