This article was posted 09/29/2006 and is most likely outdated.

Article 100 General: System Bonding Jumper
 

 
Subject - Article 100 General: System Bonding Jumper

September 29, 2006  

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General

System Bonding Jumper

A new term “system bonding jumper” was added for use with separately derived systems. Previously the term “main bonding jumper” was used to describe the bonding jumper that was installed between the metal case of a derived system and one of the separately derived system conductors.

Bonding Jumper, System. The conductor, screw or strap that bonds the metal parts (equipment grounding (bonding) conductor) of a separately derived system to the grounded conductor (typically the X0 terminal at a transformer). Figure 100-1
Author’s Comment: The system bonding jumper provides the low-impedance path to the source neutral for fault current to facilitate the clearing of the fault by opening the circuit protection device. For more information see 250.4(A)(5), 250.28 and 250.30(A)(1).


Figure 100-1
(Click on image to enlarge)

       

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Comments

  • Just wanted to add a few more comments related to this issue:

    1. The system bonding jumper should be sized based on Table 250.66 vs. Table 250.122; and, the size is not limited to a max of 3/0 AWG as it is for a grounding electrode conductor.

    2. The system bonding jumper is larger (normally) than an equipment grounding conductor since it must carry the return fault current of the unprotected phase conductors between the source (e.g., transformer secondary) and the first means of disconnect/OCDP on the SECONDARY, sufficiently long and without failure, to allow the OCPD on the PRIMARY side of the source to open and clear the fault.

    Tom
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