(3) Grounding Electrode Conductor, Single Separately Derived System. Where an equipment bonding jumper is run to the secondary system disconnecting means, it must be sized in accordance with Table 250.66, based on the area of the largest ungrounded secondary conductor. Įxception 2: A system bonding jumper can be installed at both the separately derived system and the secondary system disconnecting means where doing so doesn’t establish a parallel path for neutral current.įor all practical purposes, this isn’t possible except in a wood frame building that doesn’t have any conductive metal. In addition, the system bonding jumper must be installed at the same location where the grounding electrode conductor terminates to the grounded neutral terminal of the separately derived system, which can be at the separately derived system, the first system disconnecting means, or any point in between - but not at more than one location. The system bonding jumper can be installed at the separately derived system, the first system disconnecting means, or any point in between the separately derived system and the first disconnecting means - but not at both locations. The system bonding jumper must be sized in accordance with Table 250.66, based on the area of the largest ungrounded secondary conductor. Bonding the metal parts of the separately derived system to the secondary grounded neutral terminal by the installation of a system bonding jumper ensures that dangerous voltage from a secondary ground fault can be quickly removed by opening the secondary circuit’s overcurrent protection device. Separately derived systems must be system bonded and grounded in accordance with the following:Ī neutral-to-case bond must not be on the load side of the system bonding jumper, except as permitted by 250.142(B). Generators that supply a transfer switch that opens the grounded neutral conductor would be considered separately derived. All transformers, except autotransformers, are separately derived because the primary circuit conductors do not have any direct electrical connection to the secondary circuit conductors. A separately derived system is a premises wiring system with no direct electrical connection to conductors originating from another system.
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