6.3 Grounding and 0 V

Where the 0 V reference of a row runs, across its power domains, and how it meets protective earth and the next case. Every patch cable and every coaxial cable joins the 0 V of the two products it connects, so the products in a system share one 0 V whether or not anyone planned it; this clause makes that shared reference predictable.

EIS · Grounding: one 0 V for the bus, the DC rail, and the jacks; one bond to earth supply 0 V terminal one earth bond bus board: every header's 0 V on one 0 V (GND-002) module 0 V module 0 V module dual-source DC adapter floating −V = 0 V Every 0 V pin of a module's header is tied to its 0 V (GND-001). With a DC entry, the DC rail's −V is the product's 0 V (GND-001). A supply publishes where its 0 V meets protective earth (GND-003). Patch sleeves and coax shells join the 0 V of the products they connect. A second earth bond makes a loop: hum on audio, slow bars on a picture.

In a row

A product shall connect every 0 V pin of its power headers and PWR-A6 entries, and the −V of its DC entry, to its 0 V (GND-001). The header's 0 V pins share the return current of all three bus rails, and a module that uses only some of them puts that current through fewer contacts. A module that runs from either of two power entries has one reference for its signals whichever is connected, and a supply that takes PWR-DC12 and delivers the bus keeps both domains on one 0 V. A bus board shall join the 0 V pins of every header to one 0 V that runs to the supply's 0 V terminal (GND-002).

EIS recommends keeping any panel-mounted part whose body touches the panel free of a connection to the module's 0 V; an insulated jack (7.1) meets that.

Protective earth

A power supply shall publish whether its 0 V output is connected to protective earth, and where (GND-003). A built-in supply publishes the same in the enclosure's documentation. Mains safety, including the bonding of a metal case to protective earth, follows the safety standard the supply or case is certified to, not EIS.

EIS recommends one bond between the bus 0 V and protective earth in a system, at the supply, so that the 0 V of a row cannot carry mains-frequency current between two earth points. A DC adapter whose output floats, the usual Class II desktop adapter, adds no second bond.

EIS recommends that chassis ground carry only metalwork and screens and bond to 0 V at one point: at the supply or at the bus board, not independently at both. The bond itself is a ring terminal on bare metal under a toothed lock washer, 14 AWG or a bus bar (PWR-008, 6.1).

The front panels and rails of a case are bonded to each other by the mounting screws. With insulated jacks (7.1), the panel carries no signal return, and bonding the case metal to the supply's earth terminal, where it has one, is a shielding choice rather than a signal path.

Between cases

A patch cable or a VID-75 cable between two cases joins their 0 V through its sleeve or shell (V75-002). EIS recommends that the cases of one system take their 0 V from supplies that are all bonded to protective earth at the same outlet strip, or all floating, and that a system spread over several cases join their 0 V with one short, heavy conductor rather than through signal cables alone. A loop through two earth bonds shows as hum on audio and as slow-moving horizontal bars on a picture.

Annex O covers the heat a row's current becomes; the currents published under 6.1 are the same figures.