Just Learning And Planning

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  #1  
Old 09-12-05, 03:00 PM
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Just Learning And Planning

I would like to add a sub panel inside my garage. The main service is a 200 amp and all but one slot is taken.

At this point I am just trying to learn and plan.

The sub panel will be within 4 feet of the main panel.

I know I would have to relocate one or two circuts to the new panel to make room for the sub panel feed.

At this point there will be only one circut along the back of a work bench. Only hand power tools will be used on this circut.

Ultimately I would like to add a spa to the home. The spa would need a 50 amp circut.

I would want the subpanel to be large enough to handle this.

What size subpanel would I need. What size conductors to feed the sub panel. What size breaker in the main box.

Any help in learing would be appreciated.
 
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Old 09-12-05, 03:06 PM
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It's usually much better to keep large loads on the main panel. So if you plan to add a spa later, I'd recommend you move enough small circuits to the subpanel to make room not only for the feeder breaker but also for the spa breaker.

In this way, you could probably get by with a 6/3 feeder and a 60-amp subpanel. Of course, I don't know what other reasons you might have for the subpanel, nor what other additional loads you might plan.
 
  #3  
Old 09-12-05, 03:15 PM
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Would there be a problem if I were to use a 100 amp breaker to feed a 125 amp sub panel, or is this to much overkill?
 
  #4  
Old 09-12-05, 03:17 PM
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You can certainly use a 100 amp breaker to feed a 125 volt sub panel, but you will need larger wire than 6/3. It is probably overkill, as you suspect.
 
  #5  
Old 09-12-05, 03:20 PM
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Since the sub panel will only be about 4' from the main cost will not be a problem.

What size wire would you suggest.
 
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Old 09-12-05, 03:31 PM
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I don't think it's overkill so much as when will you grow into it. 30 years ago, a 200A residential service was rare and now most contractors won't install anything less and 400A services are common.

Over such a sort distance, I would probably go with the 100A subpanel as wire cost will only be slightly higher than a 60A panel. That would give you the flexibility to install a dust collector, welding machine, air compressor and other such toys that tend to end up in our garages.
 
  #7  
Old 09-12-05, 03:45 PM
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OK so basically I can use a 100 amp breaker that will have one common one ground and two hot. The common and the ground can be attached to the same bus bar in the main panel, correct so far.

I can use a 125 amp subpanel.

Once the conductors enter the subpanel, the common and ground are separated, each with its own bus bar, correct.


I would rather grow into the electrical work than have to come back and upgrade. Is this a bad thought?

What size conductor from the 100 amp circut breaker in the main to the subpanel.

Whats the difference between a lug panel, and a load center?
 
  #8  
Old 09-12-05, 06:21 PM
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You are correct that cost isn't much of a factor over such a short distance. Nevertheless, it will be more difficult working with the larger wire. You need #2 copper if you use a cable assembly, or #3 copper if you use individual conductors in conduit. Use a panel with plenty of spaces. Don't skimp here.

You can use a MLO (main lug only) panel since you won't need a separate disconnect in the subpanel.

Throw away the bonding screw or strap that comes with your subpanel.

Buy a subpanel that already has separate grounding and neutral bars, or buy and install a separate grounding bar kit.
 
  #9  
Old 09-16-05, 08:01 AM
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Looking at a Square D 100 amp sub panel at Lowes.

The panel does not have a separate grounding and neutral bars.

You say to buy a grounding kit. Is the bar that is in the panel now a grounding bar or a neutral bar.

If it is a grounding bar I understand. If it is not, I don't understand.

I saw the bar kits at Lowes also. Do I install one of these and make it a neutral bar?
Help
 
  #10  
Old 09-16-05, 08:23 AM
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Panels that are sold with a single buss bar are designed such that the bar can be used as either a neutral bar or as a ground bar. They come with a green screw.

The buss bar is initially not electrically connected to the panel itself. By tightening down the green screw you make an electrical connection between the bar and the panel box. This means that the bar becomes a ground bar. Since you want the ground and neutral to be connected in your main panel, this means that the bar serves either purpose.

You can but additional buss bars for the panel. The buss bars are ground bars because they attach directly to the panel and are not electrically isolated from the panel.

For your application, buy a ground bar for the panel. Throw away the green screw. Use the original bar as a neutral bar and the new bar you buy as a ground bar.
 
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