Subpanel theory


Old 08-29-04, 09:52 PM
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Subpanel theory

I am using a main panel as a subpanel in my detached garage. I understand that I am supposed to remove the bond between the neutral bus bar and the ground bus bar, which I have done.

My question is: Why aren't they still bonded by the metal housing of the subpanel. If both the grounding bus and neutral bus are screwed to the metal housing, doesn't the housing act as an electrical bond even though I have removed the bonding strip?

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Old 08-30-04, 03:21 AM
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Yes it does. If you ran 4 wires to the garage (hot,hot,neutral,ground) then you DO need to remove the bonding screw/jumper/strap. If you are using the type of panel you describe, with both bars screwed right into the back box, then you need to get another panel.
Many brands have a truly removable bonding jumper for use as you need it.
Old 08-30-04, 04:38 AM
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Are the buss bars actually screwed to the metal box, or is one and/or the other isolated by the plastic mount of the "guts" of the box?

Look closely. The innards of my subpanel "float" away from the box and the only contact point is if I use the green bonding screw.

Old 08-30-04, 06:25 AM
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Marc, this is a common misconception. Even though it may look like the neutral bar is electrically connected to the panel by virtue of its mounting, it is not. An ohmmeter can confirm this, but only, of course, if you conduct the test before the panel is all hooked up. If your panel is already connected up, maybe just for education purposes you can take your ohmmeter to the home center and try it on an empty panel.
Old 08-30-04, 03:27 PM
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There is at least one manufacturer that does screw it's bars right to the back box. Then to confuse the issue they install a strap between the bars.
I forget which company it is but I can visualize the panel clearly.
Old 08-30-04, 04:10 PM
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You are thinking of a Cutler-Hammer Panel....Roger

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