Question on sub-panel connection

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  #1  
Old 01-29-06, 12:32 PM
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Question on sub-panel connection

I am in the process of converting my carport to a garage. I have filed drawings and got permits. Added 2 120v circuits for power tools, which filled up my existing breaker panel. Now my son and I have decided we need a couple of 220v outlets, one for a welder, and one for a kiln. Since my current panel is full, I think I need to add an auxillary box/panel of some kind, and I probably should move the 2 garage circuits to that panel, so everything for the garage is in one panel. My question is " How is this done?" Where does the new box hook in to the service? Do I have enough service to the house? How do I tell what the incoming service limits are? Can I run the 220v wiring through the attic as I did the 120v? Any help you can provide will be greatly appreciated.
 
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Old 01-29-06, 01:16 PM
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Originally Posted by 1-big-dog
Added 2 120V circuits for power tools, which filled up my existing breaker panel.
What is the amperage of the MAIN breaker?


> one for a welder and one for a kiln.
Simultaneous use?


> Since my current panel is full,
> I think I need to add an auxillary box/panel of some kind,
> and I probably should move the 2 garage circuits to that panel,
> so everything for the garage is in one panel.
Yes, and pulling them out should give you room to add a new double-pole breaker for your garage subpanel.

> My question is " How is this done?"
> Where does the new box hook in to the service?
Either as a breaker in the service panel or you add a new disconnect after your meter and re-do your existing service panel to be a subpanel.



> Do I have enough service to the house?
> How do I tell what the incoming service limits are?
It's the number on your service breaker (add together in the rare chance that there is more than one service disconnect breaker).


> Can I run the 240V wiring through the attic as I did the 120v?
Yes. You need to be aware of ambient temperature limits.

You will want to run 100A (4 AWG copper {preferred} or 2 AWG aluminum {less expensive}) 4-wire feeder cable to the subpanel.
You can use conduit and THHN or a cable like SER.
The ground can be as small as 8 AWG stranded soft annealed copper.
A smaller neutral is acceptable too.

If kiln and welder will not be used at the same time, 60A feeder and breaker will do and the wires can be one size smaller.
 
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Old 01-29-06, 01:24 PM
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I would still consider a 100 amp sub-panel. If this is a typical kiln rated for a 50 amp circuit, and the same for the welder, I would not compromise the sub with on a 50 or 60 amp feed.
I do have to say though, questions like these:
Originally Posted by 1-big-dog
My question is " How is this done?" Where does the new box hook in to the service? Do I have enough service to the house? How do I tell what the incoming service limits are?
...give me the impression that this may be better left for a professional. Let an electrician install the sub-panel and you run your circuits.
 
  #4  
Old 01-29-06, 01:48 PM
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Addiitonal questions

I had originally thought to put the garage sub-panel adjacent to the house's main panel. Or would it be better to put it in the garage itself? I am wondering about several lengths of smaller wire vs one large one for all. Cost? vs convenience of having the breakers handy if they should trip. I am planning on all outlets being protected with GFIC.

I think I will get an electrician to do the sub-panel wiring, but I still need to understand how it's done, to get it right on the drawings for the modification to the permit.

Thanks for the responses!
 
  #5  
Old 01-29-06, 02:00 PM
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Any decent book on home wiring will give you the basics on a sub panel. The same book will also help you immensely when it comes to running wires for new circuits. You will need this information when running circuits, so that you don't fail the inspection.

The basics of a sub panel are (in your case) that a four wire cable connects a 240 volt breaker in the main panel to the sub panel. The four wires are the two hots, a neutral and a ground. At the sub panel the neutral and the ground remain isolated from each other.

Other than keeping the neutral and ground wires (ALL of the neutral and ground wires) separate in the sub panel, it is wired just like a main panel. You will be installing your 240 volt breakers, dedicated for the kiln and the welder, and you will be installing 120 volt breakers for lights and general purpose receptacles.

I recommend only 20 amp circuits for general purpose receptacles, and I recommend keeping the lights on a separate circuit, which can be 15 or 20 amp.

I would place the sub panel for the garage in the garage.
 
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Old 01-29-06, 02:24 PM
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Originally Posted by 1-big-dog
would it be better to put it in the garage itself?
Yes. Convenience, efficiency, and a lot neater.



> I am wondering about several lengths of smaller wire vs one large one for all.
> Cost?
The savings depends on the number of circuits, gauge, and cable or conduit type.
There is much less labor involved to run one feeder rather than 6 branches.


> convenience
That is an issue.
Plus it will be easier to expand in the future.


If your kiln is more than 30A, I recommend the 100A feed.
Also if this kiln runs for many hours per year, #3 copper will reduce energy lost in transmission.
 
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Old 01-29-06, 03:19 PM
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Further clarification needed

Thank you all for your inputs.
My panel does not have one single main breaker. (It is 30 years old).

There are 2 sections of breakers. The top 6 are all common trip ones that I understand to are 240vac. There are 3 which are 30 amp, and 2 50 amp and one 60 amp. So, if I am correct, that means that I have a 250 amp panel?

And the 14 breakers in the bottom part of the box, are organized into 7 on the left, which are one phase, and 7 on the right which is another phase. Correct?

I currently have one opening on each phase. This is easy to wire to the two circuits originally planned for the garage. But....how do I put in a double breaker with common trip in the bottom section, to run to the sub-panel? Don't the double breakers need to connect to both phases? so I can get the 240 to the garage? Sorry for all the confusion.
 
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Old 01-29-06, 03:40 PM
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Originally Posted by 1-big-dog
My panel does not have one single main breaker. (It is 30 years old).
That's not old, just atypical. What brand is it? Pushmatic?


> There are 2 sections of breakers.
> The top 6 are all common trip ones that I understand to are 240vac.
You are allowed up to 6.


> There are 3 which are 30 amp, and 2 50 amp and one 60 amp.
> So, if I am correct, that means that I have a 250 amp panel?
Unfortunately, no.
You might have 200A.
But you need to see the size of the service wire to be certain.

For what are all those breakers used?
Stove, water heater, clothes dryer, A/C, and bottom half of panel.
One more? Electric heat?



> And the 14 breakers in the bottom part of the box,
> are organized into 7 on the left, which are one phase,
> and 7 on the right which is another phase. Correct?
No. Normally, every other breaker is off the same pole of your single phase transformer.
The breakers in between are off the other pole.


> I currently have one opening on each side.
Perhaps a breaker can be moved to give you two open slots adjacent to each other.



> This is easy to wire to the two circuits originally planned for the garage.
> But....how do I put in a double breaker with common trip in the
> bottom section, to run to the sub-panel?
> Don't the double breakers need to connect to both phases?
Yes.
Instead of saying "phases", please say "poles".



> so I can get the 240 to the garage?
Yes.

Whether they will work in the lower section, I can't say.
You have a rather small panel.
30 or 40 spaces is more common for a 200A panel.
 
  #9  
Old 01-29-06, 03:58 PM
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Do NOT use the lower spaces!
You have what is called a split buss panel. Probably 100 or 150 amps. The top six two-poles are your "main" breakers. One of them feeds the whole lower section. This was a very common panel in the 50's and 60's. Everybody made them; Sq D, Wadsworth, FPE, Murray, Etc.
So if you put a 100a feeder breaker on the bottom it will be useless since it is fed off a 50.
You should SERIOUSLY consider replacing the panel, if not the whole service. There will be no efficient way to move breakers around this panel and make it work properly. Even moving the 2p30 to the bottom to make room will compromise the rest of the load.
 
  #10  
Old 01-29-06, 04:36 PM
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[QUOTE=bolide]That's not old, just atypical. What brand is it? Pushmatic?

The cover sez Cutler-Hammer.

But I guess Speedy Petey hit the nail on the head....I need to replace the panel.

Thanks all for your inputs.
 
  #11  
Old 01-29-06, 05:08 PM
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I think you need to replace your main panel, and I think you need to talk to several electricians and get some ideas.

There are several ways to go.

You could put a main panel where your existing panel is now, and then put a sub panel off of it in the garage.

You could put a main panel ion the garage and a sub panel off of it where your existing panel is right now.

You could out a main breaker where your meter is and have two panels fed from it, one where your panel is ow and another in the garage.

What is best will depend on the location of your meter and the distances involved. Also, do not be afraid to think outside the box. Perhaps your service entrance could be moved. If it needs to be upgraded, then moving it isn't that difficult.

I suggest that you get several estimates, at least three, and go from there.
 
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Old 01-29-06, 05:12 PM
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Originally Posted by 1-big-dog
I guess Speedy Petey hit the nail on the head....I need to replace the panel.
Yes. The only possible exception is if there is a main at the top that is unused.

When you replace, leave lots of room for future expansion.
One option is to add an outdoor disconnect at your meter and split your panels from there especially if you might want to add more outside buildings.
This would require fewer changes to your existing panel.
 
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