" If the electric service system has its primary main breaker outside at the meter base, the neutral and ground would be bonded only at that point, not at the breaker panel. When the main disconnect is located at the meter base, the ground and neutral terminal bars must be separate and not connected, and the main bonding jumper must be removed or disconnected."
Word for word from the text in the course. I am struggling with the verbiage difference between ‘primary main breaker’ in the first sentence, and ‘main disconnect’ in the second sentence.
To me these two sentences say the same thing regarding the main disconnect breaker being outside at the meter but has two different explanations about the bonding procedure.
Any info would be appreciated.
Kris
The confusion results from improper terminology. The service disconnect is where the MBJ (main bonding jumper) is installed. Typically in a residential panel the MBJ is a green screw. So with the service disconnect next to the meter the MBJ is installed there and the sub-panel is fed with a 4-wire feeder which must have a separate EGC (equipment grounding conductor). In the sub-panel the neutral and EGC would land on separate buses. The neutral would not be bonded to the metal enclosure. There is another wrinkle to this when you have an emergency disconnect adjacent to the meter.
Now (2020 and 2023 NEC {Section 230.85}) you’re required to install an emergency disconnect on the outside of the home but you are not required to make that the service disconnect.
So you have two basic options:
Meter > EM disconnect (not service equipment) > Service Disconnect/Panel
Meter > EM/Service Disconnect
For option 1: You would go from the meter to the EM disconnect and then to the service disconnect/panel which can be the main breaker in the panel. Between the meter the EM disconnect and the panel you would only be required to have 3 conductors. The MBJ would be installed at the panel where the service disconnect (main breaker) is located. The most important part of this arrangement is the required labeling. The EM Disconnect on the outside must be labeled “Emergency Disconnect-Not Service Equipment”.
Option 2: From the meter to the EM/Service disconnect there would be 3 conductors but from the service disconnect to the panel you would need a 4 conductor feeder. The MBJ would be installed in the EM/Service Disconnect on the outside and the panel would have separate EGC and neutral buses. The neutral would not be bonded to the panel enclosure. This would require a label only at the EM/Service disconnect stating “Emergency Disconnect-Service Disconnect”.
In summary in both scenarios you would have an EM disconnect adjacent to the meter. In option 1 it would only be the EM disconnect. In option 2 it would be both the EM disconnect and the service disconnect. This brings us all the way back to the OP where the terminology (primary main breaker) needs some work. It’s easier to understand when the proper terminology is used.
According to the National Electrical Code (NEC) Article 250, bonding within an electrical panel involves connecting the neutral (grounded conductor) to the equipment grounding conductor and the panel enclosure. This connection, known as the main bonding jumper, is typically made at the main service panel or the first means of disconnect, which would be outside next to the meter.
The main bonding jumper can be a wire, bus, or screw specifically designed for this purpose. Its primary function is to provide a low-impedance path to facilitate the operation of overcurrent protective devices in the event of a ground fault.
In subpanels (panels downstream from the main disconnect (outside) or main service panel), the neutral and ground must remain separated (floating neutral). Bonding the neutral to the ground in subpanels can create parallel paths for return currents, leading to potential safety hazards and improper operation of protective devices. Therefore, only the main disconnect or main service panel should have a neutral-to-ground connection.