Old 03-02-07, 06:53 AM
Thread Starter
Join Date: Aug 2005
Location: usa
Posts: 56

I know that when wiring a subpanel you must remove the bonding screw and seperate the grounds and neutral but my question is why?
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Old 03-02-07, 07:07 AM
Join Date: Sep 2004
Location: Saint Louis
Posts: 259
Neutrals (aka grounding conductors) are meant to be carrying current. Grounded lines aren't normally carrying current, as they are a safety device.
Old 03-02-07, 07:34 AM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
I will expand on Fubar411's answer.

First, however, let me correct your statement. You only remove the bonding screw and do not use it when you have a four wire feed to the sub panel and when yiu have separate neutral and ground buss bars. if you have a three wire feed to a sub panel in detached building (such as a detached garage) then you install and use the bond screw.

When you have a four wire feed to the sub panel, the neutral wire carries any neutral current and the ground wire is only to provide a ground path between the panels. Under normal operation the ground wire does not carry current.

If you bond the neutral buss to the sub panel then you are connecting the neutral buss to the ground buss. This will cause current to flow on both the ground and neutral wires between the panels, which is NOT what you want to happen. Further, it will cause the ground at the sub panel to be at a slightly higher potential than 0 volts.
Old 03-02-07, 07:43 AM
Join Date: Sep 2000
Location: United States
Posts: 18,497
There are many other reasons too. But it would fill a book (and has) to detail them all.

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