"ground/common" connection. Is this right?

Old 01-02-05, 07:38 AM
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"ground/common" connection. Is this right?

I'm hooking up a circuit breaker panel. Both the book I have for reference and the panel itsself appear to equate the common wires and the ground wires. This is in reference to where the white and bare wires attach inside the breaker panel. The book I'm using isn't as specific as I'd like.
Inside the panel there are 3 places to hook up fat wires. Two are for black and red wires, the third is for....what, the ground or the common? The book refers to common/ground connections. Does this mean both common and ground can hook up to the same bus? I'm unfamiliar with A/C circuits and this seem counter-intuitive.
Old 01-02-05, 08:29 AM
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If you are unfamiliar with AC wiring, I strongly urge you to spend some more time reading different books on the topic. There are numerous details that must be correct in order to have a working and _safe_ electrical install, and many ways that you can 'get it to work' that appear fine but have lurking danger. 90% of an electrical install is not 'what you need to make it work', but instead 'what you need to keep things safe when something breaks'.

On to your specific question. The electrical system in your home is 'grounded'. This means that the neutral (or 'common') conductor of your supply is connected to earth using a grounding electrode ('ground rod'). This is done for safety and reliability reasons. This connection between electrical system neutral and ground is supposed to be made at a single point on your home electrical system.

Modern electrical systems also include 'equipment grounding conductors'. The job of these conductors is to maintain exposed metal of equipment at earth potential, and to carry 'fault current' back to your main panel. The equipment grounding conductors are also supposed to be connected to the electrical system neutral at a _single_ point in your home electrical system.

The system that you describe, where you have a breaker box with two 'hot' bus bars and a 'neutral' bus bar is the most commen setup. The 'neutral' bus bar serves the purpose of single place to connect all the 'neutral' wires, all of the 'equipment grounding' wires, the 'ground rod' wire, and the supply neutral. You can only do this in the main breaker panel. No where else in your home should you connect the ground and the neutral wires.

Old 01-02-05, 08:35 AM
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The critical information that we need to know are:
  1. Is this your main panel?
  2. Does this panel house the main disconnect for your property?
  3. Is this panel in a building detached from your house?
Old 01-02-05, 11:15 AM
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In answer to your questions:

1. no, it's not my main panel

2. it doesn't house the main electrical shut-off

3. This is a detached workshop that will get power from an electrical panel from my garage.

so what you're saying is that I should run both hot power sources (120v each), the neutral, and the ground from my garage to my new box separately (4 wires total)?
At the new box I should also have separate neutral and ground busses?
Old 01-02-05, 11:20 AM
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Never mind my last response. Wish us luck!!!
thanks and happy new year!
Old 01-02-05, 11:58 AM
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Yes, you need to run four wires total from the main panel to this sub panel.

At this new subpanel the grounds and neutrals MUST be separated.

The neutral must not connect to the metal box in any manner.

You must also make sure that you do not have a parallel path for the return current back to the main panel.

Please make sure that you do this properly. An improperly connected subpanel means that you may end up with current on the ground, which could be very dangerous.
Old 01-02-05, 12:18 PM
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And you need a ground rod at the detached building.

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