What is problematic is the requirement to size the bonding jumper in accordance with Table 250.66. This table is intended for sizing of the grounding electrode conductor (not the same as the bonding jumper) which is based on the size of the ungrounded service conductor at the entrance of the building. This can result in a bonding jumper much larger than a 6 AWG copper wire especially for large buildings and/or multi-family structures. Using the exception in Section 250.66(A), if a rod, plate, or pipe is used as the grounding electrode, the grounding electrode conductor need not be larger than a 6 AWG copper wire. The argument still must be made (to the local electrical inspector) that the bonding jumper be sized in a similar fashion. However, this exception is open
to interpretation and can be misused when sizing the bonding jumper. Therefore, caution is recommended when referring to this particular section of the NEC. Until these six sets of installation instructions are written with identical language, there will be confusion in the field (both installers and inspectors) and the real possibility of improperly sizing the bonding jumper. Efforts are underway to remedy this situation