Reason for Separate Common & Ground Buses in Breaker Box?

Reply

  #1  
Old 07-15-08, 05:12 PM
Member
Thread Starter
Join Date: Mar 2004
Location: CO
Posts: 577
Received 0 Votes on 0 Posts
Reason for Separate Common & Ground Buses in Breaker Box?

My house was built and wired in 1982 and inside the breaker box is one bus bar with several terminals. The bus is connected to ground and connected to each of its terminals are a white wire and its associated green wire. Guess that was okay per code back then.

All the books I've read recently show separate common and ground buses inside the breaker box, with one thick connection between them. What's the reasoning behind the "new" method?
 
Sponsored Links
  #2  
Old 07-15-08, 05:36 PM
Member
Join Date: Oct 2007
Location: Delray Beach, FL
Posts: 406
Received 0 Votes on 0 Posts
The only time that it really matters is in a subpanel where the grounds and neutrals are separated.
In the main, they go to a common bus.
Putting the whites on one side and the grounds on the other in the main is strictly aesthetics and serves no functional purpose.
 
  #3  
Old 07-15-08, 06:09 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,914
Received 24 Votes on 20 Posts
If the neutral and ground are under the same screw terminal it was not installed according to the manufacturers instructions. This was added to the Code recently to make sure more people knew the correct way to terminate the wires.

Most busses allow 2 grounds together under 1 screw. Neutral need to terminate 1 wire per screw.
 
  #4  
Old 07-16-08, 05:31 AM
Member
Thread Starter
Join Date: Mar 2004
Location: CO
Posts: 577
Received 0 Votes on 0 Posts
Hmmm.

Guess somebody did a quik-n-dirty here because:

1. The number of breakers in the box exceeds the number of screw terminals in the bus, and

2. Some screws are clamping 2 whites and 2 greens to make up for #1.
 
  #5  
Old 07-16-08, 05:46 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,914
Received 24 Votes on 20 Posts
The label inside the breaker box should tell you how many breakers are allowed to be istalled in that enclosure.
 
  #6  
Old 07-16-08, 05:56 AM
Member
Join Date: Mar 2006
Location: NE Wis / Paris France{ In France for now }
Posts: 4,808
Received 0 Votes on 0 Posts
First thing first.,,

Yes there were a change in the code due you have the netural wire for it own " hole " in the bussbar the reason why that when you have two netural wire in the " hole " and someone working on that only got one circuit is off and the other circuit still alive and when that happend it can arc under the load or if that second netual wire is part of MWBC { MultiWire Branch Circuit } is loosen up anything on 120 volt willbe becomeing 240 volt circuit and it can destory some stuff.

Now the second thing

Many breaker box will list the spefic numbers of the breaker it will allowed in the breaker box so I will give you a quick example here

QO3040M200 the 3040 stand it will take 30 full size breakers and 10 twinner breakers so total of 40 circuit but next one you will see this one,

QO42M200 the 42 mean it will take max of 42 breaker noting more after that.

It will be pretty simuair to other manufacters they will list the amout of breaker it can be used.

Merci,Marc
 
  #7  
Old 07-16-08, 08:10 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Originally Posted by Pipsisiwah View Post
What's the reasoning behind the "new" method?
The reason for isolating grounds and neutrals in subpanels is to prevent current from flowing on exposed metal surfaces. Where there's current, there's voltage; and where there's voltage, there's a potential for shock.

Consider the case where the neutral and ground are connected in a subpanel and you have a metal conduit between the panels. Because the neutral wire inside the conduit and the conduit itself are electrically connected at both ends, the electrical current will split between the two conductors in a ratio proportional to the resistance of the paths. If this is a 100A panel, you could potentially have 50A flowing safely in the wire and 50A flowing through the exposed metal conduit. This presents a situation where under the right circumstances a person touching the exposed metal conduit could receive a hazardous shock.

In an actual house, the metal conduit may not be the only charged surface. Depending on how things are wired, the objectionable current could end up on appliance frames, plumbing fixtures and the like.

The most reliable way to prevent any of this is simply to mandate that neutrals and grounds are connected at one and only one point per building. The electrical code requires that this point be the main panel.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: