Basement Subpanel Grounding Question

[chris deanes]

Hello.
Curiosity question. I recently installed a 100A subpanel in my unfinished basement. I followed to the code book to the letter and I'm curious why the subpanel box is not grounded like the main panel? The main panel ground is tied to the box with a screw and I had to remove the screw from the subpanel. The code book does not say why? I'm just curious.

Appreciate any knowledge anyone would care to share!
Cheers!
Chris

[Jim Luttrall]

Be sure you know the difference between the ground and neutral.
The only place the ground and neutral are bonded (that little screw = bonding screw) is at the service equipment. The interior panel or sub-fed panel enclosure should be bonded to the grounding conductor but the neutral should not be bonded to the ground. There should be 4 separate conductors between the service equipment and any other panels.

Do a search here on sub-panels and you will learn much about the subject and be primed for the scolding from Jerry P. on the subject of his personal pet peeve that I am sure will follow.

[chris deanes]

Thanks for reply Jim.
The neutral line to the subpanel is tied to a bar on one side of the panel and the ground is tied to a bar on the other side of the panel. My question is since the ground and neutral are bonded at the service entrance, why can't they be bonded at the subpanel? The only thing I can think off is that ground within the house is isolated from neutral so that energy looking for ground has to travel back to the point where neutral and ground are bonded. I absolutely always follow code and if I do not understand the code I have no problem paying a licensed electrician for guidance (i paid one for guidance on installing the subpanel). I asked the electrician and he knew the rules but didn't know for sure why (maybe I should reconsider using him for advice :)

Appreciate your response and have a great day!
Chris