Bonding is a complicated scenario for sure…
(1) System Bonding Jumper
An unspliced
system bonding jumper shall comply with
250.28(A)through (D). This connection shall be made at any single point on the
separately derived system from the source to the first system
disconnecting means or
overcurrent device, or it shall be made at the source of a
separately derived system that has no
disconnecting means or
overcurrent devices, in accordance with 250.30(A)(1)(a) or (A)(1)(b). The
system bonding jumper shall remain within the
enclosure where it originates. If the source is located outside the building or structure supplied, a
system bonding jumper shall be installed at the
grounding electrode connection in compliance with
250.30(C).
Exception No. 1: For systems installed in accordance with
450.6, a single
system bonding jumper connection to the tie point of the
grounded circuit conductors from each power source shall be permitted.
Exception No. 2: If a building or structure is supplied by a
feeder from an outdoor
separately derived system, a
system bonding jumper at both the source and the first
disconnecting means shall be permitted if doing so does not establish a parallel path for the
grounded conductor. If a
grounded conductor is used in this manner, it shall not be smaller than the size specified for the
system bonding jumper but shall not be required to be larger than the
ungrounded conductor(s). For the purposes of this exception, connection through the earth shall not be considered as providing a parallel path.
Exception No. 3: The size of the
system bonding jumper for a system that supplies a Class 1, Class 2, or Class 3 circuit, and is derived from a transformer rated not more than 1000 volt-amperes, shall not be smaller than the derived
ungrounded conductors and shall not be smaller than 14 AWG copper or 12 AWG aluminum.
(a)
Installed at the Source. The
system bonding jumper shall connect the
grounded conductor to the
supply-side bonding jumper and the normally non-current-carrying metal
enclosure.
(b)
Installed at the First Disconnecting Means. The
system bonding jumper shall connect the
grounded conductor to the
supply-side bonding jumper, the
disconnecting means enclosure, and the
equipment grounding conductor(s).
Exception:
Separately derived systems consisting of multiple sources of the same type that are connected in parallel shall be permitted to have the
system bonding jumper installed at the paralleling
switchgear,
switchboard, or other paralleling connection point instead of at the
disconnecting means located at each separate source.