Subpanel - Breaker requirements

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  #1  
Old 03-11-02, 11:05 AM
LambdaEnt
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Subpanel - Breaker requirements

I am installing a 220V/70A subpanel 30 feet from the main panel, through rigid pipe.

Is a breaker required at the main panel for the subpanel? If not, how should the connection be applied to the main panel?

If I have a breaker in the main panel, is a main breaker required in the subpanel?

Is 12/2 sufficient for the run to the subpanel?


Thanx!
 
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  #2  
Old 03-11-02, 11:12 AM
joelp
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Thumbs down STOP! Read this before you go on

Whoooa, 12/2? I just completed a job like this. This is not a simple DIY project. Improper wiring on the main panel can cause serious problems, fire and even death. If you are planning on using 12/2, you need to rethink what you are doing.

Do you have a copy of the NEC rules?

A 50 Amp circuit requires #6. You will need 4 wires, and the sub panel is not bonded!.

That means you need to buy a separate grounding bar to install in the panel, and not bond it. The ground and the neutral need to be separate.

If I have lost you perhaps you need to read up and seek professional guidance from a licensed electrician.
 
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Old 03-11-02, 11:15 AM
LambdaEnt
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No, you have not lost me, and I was in serious error on the wire size.

I am VERY experienced with basic wiring, and do not need a contractor. I have remodeled two homes and am working on my third. I have run many 110 and 220 circuits before.

I have simply never installed a subpanel and was needing some guidance with the proper procedure.
 
  #4  
Old 03-11-02, 11:24 AM
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Put a 70a 2 pole circuit breaker in the main to protect the wire and subpanel. use #4 awg for 70 a capacity for the hots. You will need 2 hots, 1 neutral and 1 ground. Keep the ground and neutral seperate at the sub panel.
No main breaker needed at the subpanel.
 
  #5  
Old 03-11-02, 11:24 AM
joelp
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OK, Let's start again. I was not trying to be a wise guy, but when I saw the 12/2 notation, I wanted to stop to ensure you didn't do something you would regret.

If you are installing the sub in the same structure as the house, you will use 4 wires, as I previously posted. This is powered through a circuit breaker on the main panel that acts as the service disconnect for the sub panel.

I would recommend #4 AWG, Thhn.

The sub panel is a main lug panel that will receive the wires from the circuit breaker panel on your main.

Remember, if the sub is in the same structure as the main, you will need to add a separate ground lug bar. The sub panel will have a location to mount it. Do not bond the neutral or white as code requires they run to the main panel separately.

Hope this helps.

Oh, be sure to check your Conduit Fill requirements to ensure you use the correct diameter of rigid conduit.

Hope this helps.
 
  #6  
Old 03-11-02, 11:25 AM
LambdaEnt
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Thank you.

But, do I still need a main breaker in the subpanel?
 
  #7  
Old 03-11-02, 11:31 AM
joelp
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No, the 70 Amp breaker you will put in your main to feed the sub with be your disconnect. You will need to purchase a main lug sub panel designed for this use.
 
  #8  
Old 03-11-02, 11:38 AM
LambdaEnt
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Wonderful!

Help so quickly...I am impressed.

Thank you very much...now off to Home Depot.
 
  #9  
Old 03-11-02, 11:41 AM
LambdaEnt
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One more:

You queried whether the panel was in the same sturcture. It is going to a garage, which is a detached structure, hence the rigid pipe.

Do I need to change anything in your specs?
 
  #10  
Old 03-11-02, 11:54 AM
joelp
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Smile Your welcome

You may, but you will need to check with your local inspector. While you are on, let me direct you to a link on another site that will give you some added insight.

Glad to have been of help.

http://www.handymanwire.com/cgi-bin/...c&f=2&t=001997
 
  #11  
Old 03-11-02, 01:14 PM
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You will need a ground rod (or two) at the detached structure, attached to the grounding electrode system of the main panel.
http://homewiring.tripod.com/detgarage.html
 
  #12  
Old 03-11-02, 02:11 PM
LambdaEnt
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Okay, now a bit confused, but just a bit. Let give you the whole picture.

I just replaced the roof on the garage, and had to remove the overhead rigid pipe in the process.

The buildings are only 7 feet apart! There are three existing circuits breakers on the main panel feeding the garage via the overhead rigid pipe:
220V 20A Clothes Dryer
220V 30A Water Heater
110V 15A Lights and (2) Outlets

Even though these three circuits are technically sufficient to handle the current load (and have been doing so flawlessly), I felt that it would be safer to add some additional breakers to separate the load; i.e. inside lights, outside lights, outlets, washing machine, etc. There are not enough free spaces on the main panel.

There is a grounding connection on the main panel, but I do not know if it goes to a ground rod or a water pipe.

There is an underground water pipe connecting the two buildings. Can I use this water pipe to ground the new sub-panel?
 
  #13  
Old 03-12-02, 07:38 PM
Wgoodrich
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Lambdaent, you now have a totally different animal than those that replied thought you had, MAYBE. The 7' is a tough one that only your local AHJ [electrical inspector] can answer. Technically speaking.

A detachhed accessory structure must have a main breaker if you have more than 6 branch circuits serving from that panel in that detached structure. All detached structures must have a grounding electrode system whether you have metal water pipes connecting the two or not. The main breaker must be installed either outside or nearest point of entrance inside the detached structure. If you have a noncurrent carrying conductor connecting the two buildings together such as metal water pipes which you said you do then you must install the two hot conductors a neutral conductor and an equipment grounding conductor. You must not install just three wire feeder. Because of your metal water pipe you must have a four wire feeder.

Now here is where the maybe comes into play. YOu said your building is only 7' from the main building. The plan commission would consider this as one building. If you have a board nailed to both buildings you have one building. Only person that is the final authority to make the final ruling as to whether you have a detached structure or an attached structure accoding to the NEC is your local electrical inspector. I would do nothing until you get that ruling from you electrical inspector otherwise you may be doing it over. Make a call to your Code Enforcement Office of Local Government. Ask for an official ruling from your electrical inspector. Have a nice conversation with him to get a feel of what he expects and any special local rules. Then come back in and we can get down to the nitty gritty as to what the NEC says after he or she makes that ruling.

Good Luck

Wg
 
  #14  
Old 03-13-02, 12:03 AM
LambdaEnt
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I have already checked regarding the singularity of the building. There will only be six circuits on this sub-panel.

But I am now even more unclear regarding the ground. You seemed to go back and forth.

Can the water pipe om the garage be used as the ground?

What would the fourth wire? Is that an equipment grounding conductor from the main panel, or it's own ground (water pipe)?

Thank you again.
 
  #15  
Old 03-13-02, 04:05 AM
joeh20
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breaker requirements

I know in TN where I am, that even if you supply a ground rod, my local utility insist on two eight feet apart with a continous #4 bare copper between them, be used and if a metal water pipe is longer than eight feet in contact with the earth this must be bonded to the grounding system, but serves as the primary ground but not the only ground. A water pipe could be removed at a later time by someone else, and would hence render you without a viable path to ground. I've dealt with this in an industrial service but not in residental. Maybe this helps?
 
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