Mike Dolt Enterprises
Mike Dolt Enterprises
User: mull982, Location: Chapel Hill, NC
Asked on: Thursday, March 17, 2011 at 3:30 pm EDT
Answered on: Tuesday, May 14, 2024 at 2:56 am EDT
Question: What are the requirements for grounding a 3 phase service or a seperately derived service at the main panelboard for the following:For a 3 wire service with no neutral I would assume there is nothing to ground in the main panel and the requirement would be that the system bonding jumper between the EGC and the transformer neutral would be done at the transformer? An EGC would be run from the transformer to the ground bus in the main panel. Is there any requirement to connect the ground bus in the main panel to an grounding electrode via a GECFor a 4 wire service including a neutral? I would assume that you would need to connect a system bonding jumper either at the transformer or at the main panel. I would assume that you would not want to connect this at both ends, because then you would set up a parallel path for unbalanced neutral current to flow on the ground. Is a EGC required between the transformer and main panel? If system bonding jumper is installed at transformer then is there no connection between ground bus and neutral bus at main panel?
3 Wire Service (No Neutral) System bonding jumper
Installed at the transformer, connecting the neutral to the EGC (equipment grounding conductor).
EGC
Installed from the transformer to the ground bus in the main panel.
Grounding electrode connection (GEC)
Not required at the main panel.
4 Wire Service (Neutral Included)Option 1: System Bonding at Transformer System bonding jumper
Installed at the transformer, connecting the neutral to the EGC.
EGC
Installed from the transformer to the ground bus in the main panel.
Grounding electrode connection (GEC)
Not required at the main panel.
Main panel
No connection between the ground and neutral buses.
Option 2: System Bonding at Main Panel System bonding jumper
Installed in the main panel, connecting the neutral to the ground bus.
EGC
Installed from the transformer to the main panel's neutral bus.
Grounding electrode connection (GEC)
Installed from the ground bus in the main panel to an approved grounding electrode.
Transformer
No system bonding jumper.
Additional Notes: For a 4-wire service, a GEC is only required if the system bonding is done at the main panel. If a GEC is installed, it should be connected to the same grounding electrode as the electrodes used for other grounded neutral systems on the premises. Parallel paths for unbalanced neutral current should be avoided by ensuring that the system bonding is done at only one location (transformer or main panel). Flag for review