Generator Bonding Neutral
Generator bonding neutral refers to the intentional connection of the generator's grounded conductor (neutral) to its frame or equipment grounding system at a single point, creating a single neutral-to-ground bond. This ensures a low-impedance fault path for rapid overcurrent device operation. In Canadian practice, the arrangement depends on whether the generator is bonded-neutral or floating-neutral, and whether the transfer switch switches the neutral.
On a shop floor, the generator's neutral-bonding scheme determines fault-clearing path correctness and ensures the neutral is bonded at only one point. A bonded-neutral generator requires a transfer switch that switches the neutral to prevent double bonding. A floating-neutral generator is used when grounding is established elsewhere, and the neutral is not switched. CSA guidance mandates generators be marked as 'NEUTRAL FLOATING' or 'NEUTRAL BONDED TO FRAME'. Proper bonding ensures low-impedance fault paths for safety, preventing energized metal parts and ensuring compliance with Canadian code.
- Double bonding the neutral: bonding at both the generator and service/transfer equipment creates parallel neutral currents and violates the one-point bonding principle.
- Mismatching generator type and transfer switch: using a bonded-neutral generator with a non-switched neutral transfer switch, or a floating-neutral generator where switched-neutral is required, can cause improper grounding or loss of fault-clearing path.
- Mislabeling or failing to verify the generator configuration: relying on assumptions instead of manufacturer's marking can lead to unsafe hookups; inspection bulletins stress clear identification as floating or bonded.
Is 'bonding neutral' the same as grounding the generator?
No. Bonding neutral means connecting the grounded conductor to the generator frame or bonding point; grounding refers to connection to earth via a grounding electrode system. Canadian guidance distinguishes the neutral-to-ground bond from equipment bonding, and the generator frame is bonded through the equipment bonding conductor.
Why does a bonded-neutral generator often require a switched-neutral transfer switch?
Because the system should have only one neutral-to-ground bond at any time. Switching the neutral isolates the generator's internal neutral bond when on utility power, preventing parallel neutral paths.
When is a floating-neutral generator appropriate?
When the neutral-ground bond is established elsewhere in the system, and the generator is not meant to create a second bond at its frame. Canadian guidance says a floating-neutral generator should not be grounded to a grounding electrode nor switched in the transfer switch.
What should an inspector or maintenance technician verify before energizing temporary power?
Verify the generator's nameplate/marking, confirm whether the transfer equipment switches the neutral, confirm a single neutral-to-ground bond, and verify all non-current-carrying metal parts are bonded with the equipment grounding conductor.
Why is this a safety issue on a shop floor?
Incorrect neutral bonding can leave machine frames, enclosures, or portable tools energized under fault, or cause nuisance tripping and circulating currents. The core safety objective is rapid fault clearing and prevention of exposed metal becoming live.