This article is the fifth in a 12-part series on the differences between grounding and bonding.
Let us start our discussion by focusing on the bonding requirements for services.
The metal parts of raceways and/or enclosures containing service conductors must be bonded together [Sec. 250.92(A)]. Use bonding jumpers around reducing washers and ringed knockouts for service raceways (Fig. 1). You can use standard locknuts to make mechanical connections to raceways, but you cannot use them as the bonding means [Sec. 250.92(B)].
Ensure service bonding by one of these methods [Sec. 250.92(B)]:
(1) Bond metal parts to the service neutral conductor. A main bonding jumper is required to bond the service disconnect enclosure to the service neutral conductor [Sec. 250.24(B) and Sec. 250.28]. At the service disconnect enclosure, the service neutral conductor provides the effective ground-fault current path to the power supply [Sec. 250.24(C)]; therefore, you don’t have to install a supply-side bonding jumper in PVC conduit containing service-entrance conductors [Sec. 250.142(A)(1) and Sec. 352.60, Exception No. 2].
(2) Terminate metal raceways to threaded couplings or listed threaded hubs.
(3) Terminate metal raceways to threadless fittings.
(4) Use listed devices, such as bonding-type locknuts, bushings, wedges, or bushings with bonding jumpers to the service neutral conductor. A listed bonding wedge or bushing with a bonding jumper to the service neutral conductor is required when a metal raceway containing service conductors terminates to a ringed knockout.
A supply-side bonding jumper of the wire type used for this purpose must be sized per Table 250.102(C)(1), based on the size/area of the service phase conductors within the raceway [Sec. 250.102(C)]. A bonding-type locknut, bonding wedge, or bonding bushing with a bonding jumper can be used for a metal raceway that terminates to an enclosure without a ringed knockout.
A bonding locknut differs from a standard locknut in that it contains a bonding screw with a sharp point that drives into the metal enclosure to ensure a solid connection. Bonding one end of a service raceway to the service neutral provides the necessary low-impedance fault current path to the source.
Bonding communications systems
A bonding termination device must be provided for communication systems [Art. 805], radio and TV equipment [Art. 810], CATV [Art. 820] and similar systems [Sec. 250.94]. You bond these different systems together to minimize voltage differences between them.