Propeller Head Plaza

Main service panel vs. subpanel requirements?

67.164.165.165

In Reply to: RE: About earth grounds posted by tomsyl1 on May 24, 2008 at 19:15:10

I read Dan's article, and what he's calling "earth ground" is the safety ground connection from the main service panel safety ground bus bar to literal earth. This connection is required to be there by code.
What can confuse things is that there are different requirements for main service panels and subpanels, as below.
Main service panel:
1) Safety ground and neutral buses connect together
2) Both connect to earth through either a water pipe (older houses) or a conductive rod driven into the earth (newer houses)
Subpanel:
1) Safety ground and neutral buses do not connect together
2) Safety ground does not have its own individual connection to earth
The subpanel has separate wires for neutral and safety ground that go back to the main service panel. The end result is that neutral and ground are connected together at one, and only one point - back at the main service panel. Likewise there is one and only one connection from safety ground to earth - back at the main service panel.
Having two separate earth ground connections would be dangerous, because during a lightning strike, the two points can be at very different potentials, causing a large current to flow between them that can cause fire.

Edits: 05/25/08

Follow Ups:

RE: Main service panel vs. subpanel requirements? - Dan Banquer 04:38:19 05/26/08 (0)

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