Ground and neutral bus questions

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  #1  
Old 04-08-15, 03:14 PM
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Ground and neutral bus questions

From what I understand in my main service panel there is only a ground bus (ground and neutral bus in a main panel is the same thing). So my question is when running a wire from my main panel to a sub panel in my out building. Where does the neutral and ground go in that sub panel? Would I run the white neutral wire to the neutral bus in the sub panel and the copper ground wire to the ground bus in the sub panel? Also, what makes a ground bus a ground bus? Sorry if this post sound dumb but I am a beginner when it comes to electrical. Thanks for any information.
 
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Old 04-08-15, 03:27 PM
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I'll start and others can add. First of all, the term "main service" is incorrect as you have only one "service" Sometimes the term "main panel" is used but only the word service is absolutely correct and it applies only to the first fuse or circuit breaker after the meter.

Second, you do not have a "ground" bus in the service panel but a "neutral" bus. It is true that in the service panel that ground (more properly equipment ground) and neutral is the same. No other panel (read, sub-panel) may utilize the neutral bus as equipment ground.

Would I run the white neutral wire to the neutral bus in the sub panel and the copper ground wire to the ground bus in the sub panel?
Yes. You also must remove (or not install) the "bonding" screw or link from the neutral bus to the enclosure.

Also, what makes a ground bus a ground bus?
Being bonded to the enclosure and connected to the equipment ground from the service panel. Do not make the mistake of thinking that connection to the neutral is the same, that is ONLY done at the service panel.
 
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Old 04-08-15, 03:43 PM
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Ok, thanks for the info. What is the purpose of having both a neutral and ground?
 
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Old 04-08-15, 03:50 PM
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The neutral is the return path for the electricity after leaving the load (light, heater, tool etc.) The "ground" (equipment ground) is to provide a low impedance (low
AC resistance) return path to facilitate opening the circuit breaker of fuse in case of a fault from the "hot" conductor to the metal case of the appliance.

I suggest that you buy the book, Wiring Simplified and read it cover to cover as it will answer most of your questions on how and why electrical circuits are built the way they are. It is the "bible" of electrical work for the beginner. The cost is often less than ten dollars at the big box mega-mart homecenter where you will most likely find it in the electrical aisle, NOT the books and magazines area. It is also available at many hardware stores and from on-line booksellers.
 
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Old 04-08-15, 05:59 PM
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Hi Furd,

As a layman trying to grasp the ground/neutral concept in the main panel is the following description correct:

The neutral bonding screw bonds neutral bar to the panel or enclosure. If you had a separate ground bar or ground bar kit, the attachment screws for this bar bonds it to the panel/enclosure. If the neutral bond screw mentioned above is in place then ground and neutral are bonded together (by virtue of the bonding screw's presence) via the panel/enclosure. If there is a fault or excessive load in a circuit then the path of least resistance is for electricity to flow from the hot conductor to neutral to ground? In this path is the circuit breaker and the excessive voltage trips the breaker before any damage occurs? Neutrals carry voltage back to the panel. Grounds only carry voltage in a fault situation?
 
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Old 04-08-15, 06:04 PM
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Electricity is trying to return to the source transformer, not earth.

The ground only carries fault current. The neutral is carrying the return current.
 
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Old 04-08-15, 06:07 PM
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Source transformer meaning back out to the utility pole?
 
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Old 04-08-15, 06:25 PM
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If there is a fault or excessive load in a circuit then the path of least resistance is for electricity to flow from the hot conductor to neutral to ground?
A fault and excessive load are not the exact same thing. A fault is also excessive load, but in the sense it is thousands of amps (current) for a VERY short time. Long enough to instantly trip the circuit breaker or blow a fuse. Excessive load can just be an overcurrent situation where you just have too many things plugged into the circuit.
In this path is the circuit breaker and the excessive voltage trips the breaker before any damage occurs?
Excessive current trips the breaker, not voltage.

Neutrals carry voltage back to the panel. Grounds only carry voltage in a fault situation?
Grounds carry fault current, not voltage (except for a VERY short time)
 
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Old 04-08-15, 06:25 PM
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Yes the pole (or pad) transformer.

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Old 04-08-15, 06:37 PM
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Got it. thanks ----------------------
 
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Old 04-09-15, 05:05 AM
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A bond is an intended essentially resistance free connection in the sense that if A is bonded to B and B is bonded to C then A is bonded to C. There are rules that specify when and whether the connection is sufficient for an intended purpose such as grounding. If equipment grounding conductors are connected to a separate bus bar in the panel where the first main disconnect is located, that bar is (should be) bonded to the service neutral using the metal back (frame; can) of the panel itself or using a separate metal bar or strap or even a screw in the neutral bus digging into the panel back.

A fault is an unwanted connection through which current might flow. It takes less than a tenth of an ampere to electrocute someone. Equipment grounding is generally designed so that if a fault should energize exposed metal such as an appliance's outer surfaces, the voltage relative to anything else a person might be touching would not be enough to penetrate the person's skin and/or the fault current will increase to a level that would quickly trip a breaker and cut off said current.
 

Last edited by AllanJ; 04-09-15 at 06:48 AM.
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