System Bonding Jumper
How is a system bonding jumper different from a main bonding jumper and a supply-side bonding jumper?
A main bonding jumper is the system bonding jumper at the service disconnect, connecting neutral to equipment ground. A system bonding jumper serves the same function at a separately derived system. A supply-side bonding jumper ensures continuity on the line side of overcurrent devices, distinct in location and sizing per codes.
Where must the system bonding jumper be installed for a transformer feeding shop loads under NEC/CEC?
Under NEC 250.30(A), it must be where the grounding electrode conductor terminates, either at the transformer enclosure or the first disconnecting means. Under CEC Section 10, it connects the system grounded point to non-current-carrying parts to establish a solidly grounded system, typically at the transformer from X0 to the enclosure.
How is the system bonding jumper sized, and why does that matter for safety?
Sizing is based on the ampacity of ungrounded service conductors per NEC tables. Proper sizing ensures the jumper carries full fault current without damage, maintaining low impedance for fast overcurrent device clearing. Undersizing risks melting open during faults, leaving energized enclosures.
A system bonding jumper is the intentional connection between the system grounded point (neutral) and the non-current-carrying conductive parts or equipment grounding conductors of an electrical system. It establishes a solidly grounded system and an effective ground-fault current path, typically at a service or separately derived system (SDS), ensuring fault current returns to the source to clear overcurrent devices.
On a shop floor, system bonding jumpers are critical at service disconnects and separately derived systems like transformers. At the main panel, the neutral bus bonds to the equipment grounding bus via the main bonding jumper, creating a single-point ground. For transformers feeding machinery, the jumper connects the neutral (X0) to the enclosure and EGC system, establishing a solidly grounded wye system. This low-impedance path ensures fault current trips breakers quickly, reducing shock risk. In BC, Technical Safety BC mandates only one neutral-to-ground bond per system, preventing objectionable currents on raceways and equipment. Safety audits must verify jumper presence, sizing, and location at each SDS, and ensure no downstream re-bonding occurs.
Neutral–ground bonded in multiple locations, violating single-point grounding rules and causing objectionable currents on raceways and equipment.
Missing or improperly located system bonding jumper on a separately derived system, leading to ungrounded behavior and dangerous sustained faults.
Undersized or improperly installed jumper, risking overheating or failure under fault current and preventing timely breaker operation.